path: root/doc/FileSystem.3

'\"
'\" Copyright (c) 2001 Vincent Darley
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
.so man.macros
.TH Filesystem 3 8.4 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_FSRegister, Tcl_FSUnregister, Tcl_FSData, Tcl_FSMountsChanged, Tcl_FSGetFileSystemForPath, Tcl_FSGetPathType, Tcl_FSCopyFile, Tcl_FSCopyDirectory, Tcl_FSCreateDirectory, Tcl_FSDeleteFile, Tcl_FSRemoveDirectory, Tcl_FSRenameFile, Tcl_FSListVolumes, Tcl_FSEvalFile, Tcl_FSEvalFileEx, Tcl_FSLoadFile, Tcl_FSMatchInDirectory, Tcl_FSLink, Tcl_FSLstat, Tcl_FSUtime, Tcl_FSFileAttrsGet, Tcl_FSFileAttrsSet, Tcl_FSFileAttrStrings, Tcl_FSStat, Tcl_FSAccess, Tcl_FSOpenFileChannel, Tcl_FSGetCwd, Tcl_FSChdir, Tcl_FSPathSeparator, Tcl_FSJoinPath, Tcl_FSSplitPath, Tcl_FSEqualPaths, Tcl_FSGetNormalizedPath, Tcl_FSJoinToPath, Tcl_FSConvertToPathType, Tcl_FSGetInternalRep, Tcl_FSGetTranslatedPath, Tcl_FSGetTranslatedStringPath, Tcl_FSNewNativePath, Tcl_FSGetNativePath, Tcl_FSFileSystemInfo, Tcl_AllocStatBuf \- procedures to interact with any filesystem
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_FSRegister\fR(\fIclientData, fsPtr\fR)
.sp
int
\fBTcl_FSUnregister\fR(\fIfsPtr\fR)
.sp
ClientData
\fBTcl_FSData\fR(\fIfsPtr\fR)
.sp
void
\fBTcl_FSMountsChanged\fR(\fIfsPtr\fR)
.sp
Tcl_Filesystem*
\fBTcl_FSGetFileSystemForPath\fR(\fIpathPtr\fR)
.sp
Tcl_PathType
\fBTcl_FSGetPathType\fR(\fIpathPtr\fR)
.sp
int
\fBTcl_FSCopyFile\fR(\fIsrcPathPtr, destPathPtr\fR)
.sp
int
\fBTcl_FSCopyDirectory\fR(\fIsrcPathPtr, destPathPtr, errorPtr\fR)
.sp
int
\fBTcl_FSCreateDirectory\fR(\fIpathPtr\fR)
.sp
int
\fBTcl_FSDeleteFile\fR(\fIpathPtr\fR)
.sp
int
\fBTcl_FSRemoveDirectory\fR(\fIpathPtr, int recursive, errorPtr\fR)
.sp
int
\fBTcl_FSRenameFile\fR(\fIsrcPathPtr, destPathPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSListVolumes\fR(\fIvoid\fR)
.sp
.VS 8.5
int
\fBTcl_FSEvalFileEx\fR(\fIinterp, pathPtr, encodingName\fR)
.VE 8.5
.sp
int
\fBTcl_FSEvalFile\fR(\fIinterp, pathPtr\fR)
.sp
int
\fBTcl_FSLoadFile\fR(\fIinterp, pathPtr, sym1, sym2, proc1Ptr, proc2Ptr,
               handlePtr, unloadProcPtr\fR)
.sp
int
\fBTcl_FSMatchInDirectory\fR(\fIinterp, resultPtr, pathPtr, pattern, types\fR)
.sp
Tcl_Obj*
\fBTcl_FSLink\fR(\fIlinkNamePtr, toPtr, linkAction\fR)
.sp
int
\fBTcl_FSLstat\fR(\fIpathPtr, statPtr\fR)
.sp
int
\fBTcl_FSUtime\fR(\fIpathPtr, tval\fR)
.sp
int
\fBTcl_FSFileAttrsGet\fR(\fIinterp, int index, pathPtr, objPtrRef\fR)
.sp
int
\fBTcl_FSFileAttrsSet\fR(\fIinterp, int index, pathPtr, Tcl_Obj *objPtr\fR)
.sp
const char**
\fBTcl_FSFileAttrStrings\fR(\fIpathPtr, objPtrRef\fR)
.sp
int
\fBTcl_FSStat\fR(\fIpathPtr, statPtr\fR)
.sp
int
\fBTcl_FSAccess\fR(\fIpathPtr, mode\fR)
.sp
Tcl_Channel
\fBTcl_FSOpenFileChannel\fR(\fIinterp, pathPtr, modeString, permissions\fR)
.sp
Tcl_Obj*
\fBTcl_FSGetCwd\fR(\fIinterp\fR)
.sp
int
\fBTcl_FSChdir\fR(\fIpathPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSPathSeparator\fR(\fIpathPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSJoinPath\fR(\fIlistObj, elements\fR)
.sp
Tcl_Obj*
\fBTcl_FSSplitPath\fR(\fIpathPtr, lenPtr\fR)
.sp
int
\fBTcl_FSEqualPaths\fR(\fIfirstPtr, secondPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSGetNormalizedPath\fR(\fIinterp, pathPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSJoinToPath\fR(\fIbasePtr, objc, objv\fR)
.sp
int
\fBTcl_FSConvertToPathType\fR(\fIinterp, pathPtr\fR)
.sp
ClientData
\fBTcl_FSGetInternalRep\fR(\fIpathPtr, fsPtr\fR)
.sp
Tcl_Obj *
\fBTcl_FSGetTranslatedPath\fR(\fIinterp, pathPtr\fR)
.sp
const char *
\fBTcl_FSGetTranslatedStringPath\fR(\fIinterp, pathPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSNewNativePath\fR(\fIfsPtr, clientData\fR)
.sp
const char *
\fBTcl_FSGetNativePath\fR(\fIpathPtr\fR)
.sp
Tcl_Obj*
\fBTcl_FSFileSystemInfo\fR(\fIpathPtr\fR)
.sp
Tcl_StatBuf*
\fBTcl_AllocStatBuf\fR()
.SH ARGUMENTS
.AS Tcl_FSUnloadFileProc **unloadProcPtr out
.AP Tcl_Filesystem *fsPtr in
Points to a structure containing the addresses of procedures that
can be called to perform the various filesystem operations.
.AP Tcl_Obj *pathPtr in
The path represented by this object is used for the operation in
question.  If the object does not already have an internal \fBpath\fR
representation, it will be converted to have one.
.AP Tcl_Obj *srcPathPtr in
As for \fIpathPtr\fR, but used for the source file for a copy or
rename operation.
.AP Tcl_Obj *destPathPtr in
As for \fIpathPtr\fR, but used for the destination filename for a copy or
rename operation.
.AP "const char" *encodingName in
The encoding of the data stored in the
file identified by \fIpathPtr\fR and to be evaluated.
.AP "const char" *pattern in
Only files or directories matching this pattern will be returned.
.AP Tcl_GlobTypeData *types in
Only files or directories matching the type descriptions contained in
this structure will be returned.  This parameter may be NULL.
.AP Tcl_Interp *interp in
Interpreter to use either for results, evaluation, or reporting error
messages.
.AP ClientData clientData in
The native description of the path object to create.
.AP Tcl_Obj *firstPtr in
The first of two path objects to compare.  The object may be converted
to \fBpath\fR type.
.AP Tcl_Obj *secondPtr in
The second of two path objects to compare.  The object may be converted
to \fBpath\fR type.
.AP Tcl_Obj *listObj in
The list of path elements to operate on with a \fBjoin\fR operation.
.AP int elements in
If non-negative, the number of elements in the \fIlistObj\fR which should
be joined together.  If negative, then all elements are joined.
.AP Tcl_Obj **errorPtr out
In the case of an error, filled with an object containing the name of
the file which caused an error in the various copy/rename operations.
.AP Tcl_Obj **objPtrRef out
Filled with an object containing the result of the operation.
.AP Tcl_Obj *resultPtr out
Pre-allocated object in which to store (using
\fBTcl_ListObjAppendElement\fR) the list of
files or directories which are successfully matched.
.AP int mode in
Mask consisting of one or more of R_OK, W_OK, X_OK and F_OK.  R_OK,
W_OK and X_OK request checking whether the file exists and  has  read,
write and  execute  permissions, respectively.  F_OK just requests
checking for the existence of the file.
.AP Tcl_StatBuf *statPtr out
The structure that contains the result of a stat or lstat operation.
.AP "const char" *sym1 in
Name of a procedure to look up in the file's symbol table
.AP "const char" *sym2 in
Name of a procedure to look up in the file's symbol table
.AP Tcl_PackageInitProc **proc1Ptr out
Filled with the init function for this code.
.AP Tcl_PackageInitProc **proc2Ptr out
Filled with the safe-init function for this code.
.AP ClientData *clientDataPtr out
Filled with the clientData value to pass to this code's unload
function when it is called.
.AP Tcl_LoadHandle *handlePtr out
Filled with an abstract token representing the loaded file.
.AP Tcl_FSUnloadFileProc **unloadProcPtr out
Filled with the function to use to unload this piece of code.
.AP utimbuf *tval in
The access and modification times in this structure are read and
used to set those values for a given file.
.AP "const char" *modeString in
Specifies how the file is to be accessed.  May have any of the values
allowed for the \fImode\fR argument to the Tcl \fBopen\fR command.
.AP int permissions in
POSIX-style permission flags such as 0644.  If a new file is created, these
permissions will be set on the created file.
.AP int *lenPtr out
If non-NULL, filled with the number of elements in the split path.
.AP Tcl_Obj *basePtr in
The base path on to which to join the given elements.  May be NULL.
.AP int objc in
The number of elements in \fIobjv\fR.
.AP "Tcl_Obj *const" objv[] in
The elements to join to the given base path.
.AP Tcl_Obj *linkNamePtr in
The name of the link to be created or read.
.AP Tcl_Obj *toPtr in
What the link called \fIlinkNamePtr\fR should be linked to, or NULL if
the symbolic link specified by \fIlinkNamePtr\fR is to be read.
.AP int linkAction in
OR-ed combination of flags indicating what kind of link should be
created (will be ignored if \fItoPtr\fR is NULL). Valid bits to set
are \fBTCL_CREATE_SYMBOLIC_LINK\fR and \fBTCL_CREATE_HARD_LINK\fR.
When both flags are set and the underlying filesystem can do either,
symbolic links are preferred.
.BE

.SH DESCRIPTION
.PP
There are several reasons for calling the \fBTcl_FS\fR API functions
(e.g. \fBTcl_FSAccess\fR and \fBTcl_FSStat\fR)
rather than calling system level functions like \fBaccess\fR and
\fBstat\fR directly.  First, they will work cross-platform, so an
extension which calls them should work unmodified on Unix and
Windows.  Second, the Windows implementation of some of these functions
fixes some bugs in the system level calls.  Third, these function calls
deal with any
.QW "Utf to platform-native"
path conversions which may be
required (and may cache the results of such conversions for greater
efficiency on subsequent calls).  Fourth, and perhaps most importantly,
all of these functions are
.QW "virtual filesystem aware" .
Any virtual filesystem (VFS for short) which has been registered (through
\fBTcl_FSRegister\fR) may reroute file access to alternative
media or access methods.  This means that all of these functions (and
therefore the corresponding \fBfile\fR, \fBglob\fR, \fBpwd\fR, \fBcd\fR,
\fBopen\fR, etc.  Tcl commands) may be operate on
.QW files
which are not
native files in the native filesystem.  This also means that any Tcl
extension which accesses the filesystem (FS for short) through this API is
automatically
.QW "virtual filesystem aware" .
Of course, if an extension
accesses the native filesystem directly (through platform-specific
APIs, for example), then Tcl cannot intercept such calls.
.PP
If appropriate VFSes have been registered, the
.QW files
may, to give two
examples, be remote (e.g. situated on a remote ftp server) or archived
(e.g. lying inside a .zip archive).  Such registered filesystems provide
a lookup table of functions to implement all or some of the functionality
listed here.  Finally, the \fBTcl_FSStat\fR and \fBTcl_FSLstat\fR calls
abstract away from what the
.QW "struct stat"
buffer is actually
declared to be, allowing the same code to be used both on systems with
and systems without support for files larger than 2GB in size.
.PP
The \fBTcl_FS\fR API is objectified and may cache internal
representations and other path-related strings (e.g. the current working
directory).  One side-effect of this is that one must not pass in objects
with a reference count of zero to any of these functions.  If such calls were
handled, they might result
in memory leaks (under some circumstances, the filesystem code may wish
to retain a reference to the passed in object, and so one must not assume
that after any of these calls return, the object still has a reference count of
zero - it may have been incremented) or in a direct segmentation fault
(or other memory access error)
due to the object being freed part way through the complex object
manipulation required to ensure that the path is fully normalized and
absolute for filesystem determination.  The practical lesson to learn
from this is that
.CS
Tcl_Obj *path = Tcl_NewStringObj(...);
Tcl_FS\fIWhatever\fR(path);
Tcl_DecrRefCount(path);
.CE
is wrong, and may cause memory errors. The \fIpath\fR must have its
reference count incremented before passing it in, or
decrementing it.  For this reason, objects with a reference count of zero are
considered not to be valid filesystem paths and calling any Tcl_FS API
function with such an object will result in no action being taken.
.SS "FS API FUNCTIONS"
\fBTcl_FSCopyFile\fR attempts to copy the file given by \fIsrcPathPtr\fR to the
path name given by \fIdestPathPtr\fR.  If the two paths given lie in the same
filesystem (according to \fBTcl_FSGetFileSystemForPath\fR) then that
filesystem's
.QW "copy file"
function is called (if it is non-NULL).
Otherwise the function returns -1 and sets the \fBerrno\fR global C
variable to the
.QW EXDEV
POSIX error code (which signifies a
.QW "cross-domain link" ).
.PP
\fBTcl_FSCopyDirectory\fR attempts to copy the directory given by \fIsrcPathPtr\fR to the
path name given by \fIdestPathPtr\fR.  If the two paths given lie in the same
filesystem (according to \fBTcl_FSGetFileSystemForPath\fR) then that
filesystem's
.QW "copy file"
function is called (if it is non-NULL).
Otherwise the function returns -1 and sets the \fBerrno\fR global C
variable to the
.QW EXDEV
POSIX error code (which signifies a
.QW "cross-domain link" ).
.PP
\fBTcl_FSCreateDirectory\fR attempts to create the directory given by
\fIpathPtr\fR by calling the owning filesystem's
.QW "create directory"
function.
.PP
\fBTcl_FSDeleteFile\fR attempts to delete the file given by
\fIpathPtr\fR by calling the owning filesystem's
.QW "delete file"
function.
.PP
\fBTcl_FSRemoveDirectory\fR attempts to remove the directory given by
\fIpathPtr\fR by calling the owning filesystem's
.QW "remove directory"
function.
.PP
\fBTcl_FSRenameFile\fR attempts to rename the file or directory given by
\fIsrcPathPtr\fR to the path name given by \fIdestPathPtr\fR.  If the two paths
given lie in the same filesystem (according to
\fBTcl_FSGetFileSystemForPath\fR) then that filesystem's
.QW "rename file"
function is called (if it is non-NULL).  Otherwise the function returns -1
and sets the \fBerrno\fR global C variable to the
.QW EXDEV
POSIX error code (which signifies a
.QW "cross-domain link" ).
.PP
\fBTcl_FSListVolumes\fR calls each filesystem which has a non-NULL
.QW "list volumes"
function and asks them to return their list of root volumes.  It
accumulates the return values in a list which is returned to the
caller (with a reference count of 0).
.PP
.VS 8.5
\fBTcl_FSEvalFileEx\fR reads the file given by \fIpathPtr\fR using
the encoding identified by \fIencodingName\fR and evaluates
its contents as a Tcl script.  It returns the same information as
\fBTcl_EvalObjEx\fR.
If \fIencodingName\fR is NULL, the system encoding is used for
reading the file contents.
If the file could not be read then a Tcl error is returned to describe
why the file could not be read.
The eofchar for files is
.QW \e32
(^Z) for all platforms.
If you require a
.QW ^Z
in code for string comparison, you can use
.QW \e032
or
.QW \eu001a ,
which will be safely substituted by the Tcl interpreter into
.QW ^Z .
\fBTcl_FSEvalFile\fR is a simpler version of
\fBTcl_FSEvalFileEx\fR that always uses the system encoding
when reading the file.
.VE 8.5
.PP
\fBTcl_FSLoadFile\fR dynamically loads a binary code file into memory and
returns the addresses of two procedures within that file, if they are
defined.  The appropriate function for the filesystem to which \fIpathPtr\fR
belongs will be called.  If that filesystem does not implement this
function (most virtual filesystems will not, because of OS limitations
in dynamically loading binary code), Tcl will attempt to copy the file
to a temporary directory and load that temporary file.
.PP
Returns a standard Tcl completion code.  If an error occurs, an error
message is left in the \fIinterp\fR's result.
.PP
\fBTcl_FSMatchInDirectory\fR is used by the globbing code to search a
directory for all files which match a given pattern.  The appropriate
function for the filesystem to which \fIpathPtr\fR belongs will be called.
.PP
The return value is a standard Tcl result indicating whether an error
occurred in globbing.  Error messages are placed in interp (unless 
interp is NULL, which is allowed), but good results are placed in the 
resultPtr given.
.PP
Note that the \fBglob\fR code implements recursive patterns internally, so
this function will only ever be passed simple patterns, which can be
matched using the logic of \fBstring match\fR.  To handle recursion, Tcl
will call this function frequently asking only for directories to be
returned.  A special case of being called with a NULL pattern indicates
that the path needs to be checked only for the correct type.
.PP
\fBTcl_FSLink\fR replaces the library version of \fBreadlink\fR, and
extends it to support the creation of links.  The appropriate function
for the filesystem to which \fIlinkNamePtr\fR belongs will be called.
.PP
If the \fItoPtr\fR is NULL, a
.QW "read link"
action is performed.  The result
is a Tcl_Obj specifying the contents of the symbolic link given by
\fIlinkNamePtr\fR, or NULL if the link could not be read.  The result is owned
by the caller, which should call Tcl_DecrRefCount when the result is no
longer needed.  If the \fItoPtr\fR is not NULL, Tcl should create a link
of one of the types passed in in the \fIlinkAction\fR flag.  This flag is
an ORed combination of \fBTCL_CREATE_SYMBOLIC_LINK\fR and \fBTCL_CREATE_HARD_LINK\fR.
Where a choice exists (i.e. more than one flag is passed in), the Tcl
convention is to prefer symbolic links.  When a link is successfully
created, the return value should be \fItoPtr\fR (which is therefore
already owned by the caller).  If unsuccessful, NULL is returned.
.PP
\fBTcl_FSLstat\fR fills the stat structure \fIstatPtr\fR with information
about the specified file.  You do not need any access rights to the
file to get this information but you need search rights to all
directories named in the path leading to the file.  The stat structure
includes info regarding device, inode (always 0 on Windows),
privilege mode, nlink (always 1 on Windows), user id (always 0 on
Windows), group id (always 0 on Windows), rdev (same as device on
Windows), size, last access time, last modification time, and
last metadata change time.
.PP
If \fIpath\fR exists, \fBTcl_FSLstat\fR returns 0 and the stat structure
is filled with data.  Otherwise, -1 is returned, and no stat info is
given.
.PP
\fBTcl_FSUtime\fR replaces the library version of utime.
.PP
This returns 0 on success and -1 on error (as per the \fButime\fR
documentation).  If successful, the function
will update the
.QW atime
and
.QW mtime
values of the file given.
.PP
\fBTcl_FSFileAttrsGet\fR implements read access for the hookable \fBfile
attributes\fR subcommand.  The appropriate function for the filesystem to
which \fIpathPtr\fR belongs will be called.
.PP
If the result is \fBTCL_OK\fR, then an object was placed in
\fIobjPtrRef\fR, which
will only be temporarily valid (unless \fBTcl_IncrRefCount\fR is called).
.PP
\fBTcl_FSFileAttrsSet\fR implements write access for the hookable \fBfile
attributes\fR subcommand.  The appropriate function for the filesystem to
which \fIpathPtr\fR belongs will be called.
.PP
\fBTcl_FSFileAttrStrings\fR implements part of the hookable \fBfile
attributes\fR subcommand.  The appropriate function for the filesystem
to which \fIpathPtr\fR belongs will be called.
.PP
The called procedure may either return an array of strings, or may
instead return NULL and place a Tcl list into the given \fIobjPtrRef\fR.  Tcl
will take that list and first increment its reference count before using it.
On completion of that use, Tcl will decrement its reference count.  Hence if
the list should be disposed of by Tcl when done, it should have a
reference count of zero, and if the list should not be disposed of, the
filesystem should ensure it retains a reference count to the object.
.PP
\fBTcl_FSAccess\fR checks whether the process would be allowed to read,
write or test for existence of the file (or other filesystem object)
whose name is \fIpathname\fR.   If \fIpathname\fR is a symbolic link on Unix,
then permissions of the file referred by this symbolic link are
tested.
.PP
On success (all requested permissions granted), zero is returned.  On
error (at least one bit in mode asked for a permission that is denied,
or some other error occurred), -1 is returned.
.PP
\fBTcl_FSStat\fR fills the stat structure \fIstatPtr\fR with information
about the specified file.  You do not need any access rights to the
file to get this information but you need search rights to all
directories named in the path leading to the file.  The stat structure
includes info regarding device, inode (always 0 on Windows),
privilege mode, nlink (always 1 on Windows), user id (always 0 on
Windows), group id (always 0 on Windows), rdev (same as device on
Windows), size, last access time, last modification time, and
last metadata change time.
.PP
If \fIpath\fR exists, \fBTcl_FSStat\fR returns 0 and the stat structure
is filled with data.  Otherwise, -1 is returned, and no stat info is
given.
.PP
\fBTcl_FSOpenFileChannel\fR opens a file specified by \fIpathPtr\fR and
returns a channel handle that can be used to perform input and output on
the file. This API is modeled after the \fBfopen\fR procedure of
the Unix standard I/O library.
The syntax and meaning of all arguments is similar to those
given in the Tcl \fBopen\fR command when opening a file.
If an error occurs while opening the channel, \fBTcl_FSOpenFileChannel\fR
returns NULL and records a POSIX error code that can be
retrieved with \fBTcl_GetErrno\fR.
In addition, if \fIinterp\fR is non-NULL, \fBTcl_FSOpenFileChannel\fR
leaves an error message in \fIinterp\fR's result after any error.
.PP
The newly created channel is not registered in the supplied interpreter; to
register it, use \fBTcl_RegisterChannel\fR.
If one of the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it as a
replacement for the standard channel.
.PP
\fBTcl_FSGetCwd\fR replaces the library version of \fBgetcwd\fR.
.PP
It returns the Tcl library's current working directory.  This may be
different to the native platform's working directory, which happens when
the current working directory is not in the native filesystem.
.PP
The result is a pointer to a Tcl_Obj specifying the current directory,
or NULL if the current directory could not be determined.  If NULL is
returned, an error message is left in the \fIinterp\fR's result.
.PP
The result already has its reference count incremented for the caller.  When
it is no longer needed, that reference count should be decremented.  This is
needed for thread-safety purposes, to allow multiple threads to access
this and related functions, while ensuring the results are always
valid.
.PP
\fBTcl_FSChdir\fR replaces the library version of \fBchdir\fR.  The path is
normalized and then passed to the filesystem which claims it.  If that
filesystem does not implement this function, Tcl will fallback to a
combination of \fBstat\fR and \fBaccess\fR to check whether the directory
exists and has appropriate permissions.
.PP
For results, see \fBchdir\fR documentation.  If successful, we keep a
record of the successful path in \fIcwdPathPtr\fR for subsequent calls to
\fBTcl_FSGetCwd\fR.
.PP
\fBTcl_FSPathSeparator\fR returns the separator character to be used for
most specific element of the path specified by \fIpathPtr\fR (i.e. the last
part of the path).
.PP
The separator is returned as a Tcl_Obj containing a string of length
1.  If the path is invalid, NULL is returned.
.PP
\fBTcl_FSJoinPath\fR takes the given Tcl_Obj, which must be a valid
list (which is allowed to have a reference count of zero), and returns the path
object given by considering the first \fIelements\fR elements as valid path
segments (each path segment may be a complete path, a partial path or
just a single possible directory or file name).  If any path segment is
actually an absolute path, then all prior path segments are discarded.
If \fIelements\fR is less than 0, we use the entire list.
.PP
It is possible that the returned object is actually an element
of the given list, so the caller should be careful to increment the
reference count of the result before freeing the list.
.PP
The returned object, typically with a reference count of zero (but it
could be shared
under some conditions), contains the joined path.  The caller must
add a reference count to the object before using it.  In particular, the
returned object could be an element of the given list, so freeing the
list might free the object prematurely if no reference count has been taken.
If the number of elements is zero, then the returned object will be
an empty-string Tcl_Obj.
.PP
\fBTcl_FSSplitPath\fR takes the given Tcl_Obj, which should be a valid path,
and returns a Tcl list object containing each segment of that path as
an element.
It returns a list object with a reference count of zero.  If the
passed in \fIlenPtr\fR is non-NULL, the variable it points to will be
updated to contain the number of elements in the returned list.
.PP
\fBTcl_FSEqualPaths\fR tests whether the two paths given represent the same
filesystem object
.PP
It returns 1 if the paths are equal, and 0 if they are different.  If
either path is NULL, 0 is always returned.
.PP
\fBTcl_FSGetNormalizedPath\fR this important function attempts to extract
from the given Tcl_Obj a unique normalized path representation, whose
string value can be used as a unique identifier for the file.
.PP
It returns the normalized path object, owned by Tcl, or NULL if the path
was invalid or could otherwise not be successfully converted.
Extraction of absolute, normalized paths is very efficient (because the
filesystem operates on these representations internally), although the
result when the filesystem contains numerous symbolic links may not be
the most user-friendly version of a path.  The return value is owned by
Tcl and has a lifetime equivalent to that of the \fIpathPtr\fR passed in
(unless that is a relative path, in which case the normalized path
object may be freed any time the cwd changes) - the caller can of
course increment the refCount if it wishes to maintain a copy for longer.
.PP
\fBTcl_FSJoinToPath\fR takes the given object, which should usually be a
valid path or NULL, and joins onto it the array of paths segments
given.
.PP
Returns object, typically with refCount of zero (but it could be shared
under some conditions), containing the joined path.  The caller must
add a refCount to the object before using it.  If any of the objects
passed into this function (pathPtr or path elements) have a refCount
of zero, they will be freed when this function returns.
.PP
\fBTcl_FSConvertToPathType\fR tries to convert the given Tcl_Obj to a valid
Tcl path type, taking account of the fact that the cwd may have changed
even if this object is already supposedly of the correct type.
The filename may begin with
.QW ~
(to indicate current user's home directory) or
.QW ~<user>
(to indicate any user's home directory).
.PP
If the conversion succeeds (i.e. the object is a valid path in one of
the current filesystems), then \fBTCL_OK\fR is returned.  Otherwise
\fBTCL_ERROR\fR is returned, and an error message may
be left in the interpreter.
.PP
\fBTcl_FSGetInternalRep\fR extracts the internal representation of a given
path object, in the given filesystem.  If the path object belongs to a
different filesystem, we return NULL. If the internal representation is
currently NULL, we attempt to generate it, by calling the filesystem's
\fBTcl_FSCreateInternalRepProc\fR.
.PP
Returns NULL or a valid internal path representation.  This internal
representation is cached, so that repeated calls to this function will
not require additional conversions.
.PP
\fBTcl_FSGetTranslatedPath\fR attempts to extract the translated path
from the given Tcl_Obj.
.PP
If the translation succeeds (i.e. the object is a valid path), then it is
returned.  Otherwise NULL will be returned, and an error message may be
left in the interpreter.  A
.QW translated
path is one which contains no
.QW ~
or
.QW ~user
sequences (these have been expanded to their current
representation in the filesystem).  The object returned is owned by the
caller, which must store it or call Tcl_DecrRefCount to ensure memory is
freed.  This function is of little practical use, and
\fBTcl_FSGetNormalizedPath\fR or \fBTcl_GetNativePath\fR are usually
better functions to use for most purposes.
.PP
\fBTcl_FSGetTranslatedStringPath\fR does the same as
\fBTcl_FSGetTranslatedPath\fR, but returns a character string or NULL.
The string returned is dynamically allocated and owned by the caller,
which must store it or call \fBckfree\fR to ensure it is freed.  Again,
\fBTcl_FSGetNormalizedPath\fR or \fBTcl_GetNativePath\fR are usually
better functions to use for most purposes.
.PP
\fBTcl_FSNewNativePath\fR performs something like the reverse of the
usual obj->path->nativerep conversions.  If some code retrieves a path
in native form (from, e.g. \fBreadlink\fR or a native dialog), and that path
is to be used at the Tcl level, then calling this function is an
efficient way of creating the appropriate path object type.
.PP
The resulting object is a pure
.QW path
object, which will only receive
a UTF-8 string representation if that is required by some Tcl code.
.PP
\fBTcl_FSGetNativePath\fR is for use by the Win/Unix native
filesystems, so that they can easily retrieve the native (char* or
TCHAR*) representation of a path.  This function is a convenience
wrapper around \fBTcl_FSGetInternalRep\fR, and assumes the native
representation is string-based.  It may be desirable in the future to
have non-string-based native representations (for example, on MacOSX, a
representation using a fileSpec of FSRef structure would probably be
more efficient).  On Windows a full Unicode representation would allow
for paths of unlimited length.  Currently the representation is simply a
character string which may contain either the relative path or a
complete, absolute normalized path in the native encoding (complex
conditions dictate which of these will be provided, so neither can be
relied upon, unless the path is known to be absolute).  If you need a
native path which must be absolute, then you should ask for the native
version of a normalized path.  If for some reason a non-absolute,
non-normalized version of the path is needed, that must be constructed
separately (e.g. using \fBTcl_FSGetTranslatedPath\fR).
.PP
The native representation is cached so that repeated calls to this
function will not require additional conversions.  The return value is
owned by Tcl and has a lifetime equivalent to that of the \fIpathPtr\fR
passed in (unless that is a relative path, in which case the native
representation may be freed any time the cwd changes).
.PP
\fBTcl_FSFileSystemInfo\fR returns a list of two elements.  The first
element is the name of the filesystem (e.g.
.QW native ,
.QW vfs ,
.QW zip ,
or
.QW prowrap ,
perhaps), and the second is the particular type of the
given path within that filesystem (which is filesystem dependent).  The
second element may be empty if the filesystem does not provide a
further categorization of files.
.PP
A valid list object is returned, unless the path object is not
recognized, when NULL will be returned.
.PP
\fBTcl_FSGetFileSystemForPath\fR returns the a pointer to the
\fBTcl_Filesystem\fR which accepts this path as valid.
.PP
If no filesystem will accept the path, NULL is returned.
.PP
\fBTcl_FSGetPathType\fR determines whether the given path is relative
to the current directory, relative to the current volume, or
absolute.
.PP
It returns one of \fBTCL_PATH_ABSOLUTE\fR, \fBTCL_PATH_RELATIVE\fR, or
\fBTCL_PATH_VOLUME_RELATIVE\fR
.PP
\fBTcl_AllocStatBuf\fR allocates a \fITcl_StatBuf\fR on the system
heap (which may be deallocated by being passed to \fBckfree\fR.)  This
allows extensions to invoke \fBTcl_FSStat\fR and \fBTcl_FSLStat\fR
without being dependent on the size of the buffer.  That in turn
depends on the flags used to build Tcl.
.SH "THE VIRTUAL FILESYSTEM API"
.PP
A filesystem provides a \fBTcl_Filesystem\fR structure that contains
pointers to functions that implement the various operations on a
filesystem; these operations are invoked as needed by the generic
layer, which generally occurs through the functions listed above.
.PP
The \fBTcl_Filesystem\fR structures are manipulated using the following
methods.
.PP
\fBTcl_FSRegister\fR takes a pointer to a filesystem structure and an
optional piece of data to associated with that filesystem.  On calling
this function, Tcl will attach the filesystem to the list of known
filesystems, and it will become fully functional immediately.  Tcl does
not check if the same filesystem is registered multiple times (and in
general that is not a good thing to do).  \fBTCL_OK\fR will be returned.
.PP
\fBTcl_FSUnregister\fR removes the given filesystem structure from
the list of known filesystems, if it is known, and returns \fBTCL_OK\fR.  If
the filesystem is not currently registered, \fBTCL_ERROR\fR is returned.
.PP
\fBTcl_FSData\fR will return the ClientData associated with the given
filesystem, if that filesystem is registered.  Otherwise it will
return NULL.
.PP
\fBTcl_FSMountsChanged\fR is used to inform the Tcl's core that
the set of mount points for the given (already registered) filesystem
have changed, and that cached file representations may therefore no
longer be correct.
.SS "THE TCL_FILESYSTEM STRUCTURE"
.PP
The \fBTcl_Filesystem\fR structure contains the following fields:
.CS
typedef struct Tcl_Filesystem {
    const char *\fItypeName\fR;
    int \fIstructureLength\fR;
    Tcl_FSVersion \fIversion\fR;
    Tcl_FSPathInFilesystemProc *\fIpathInFilesystemProc\fR;
    Tcl_FSDupInternalRepProc *\fIdupInternalRepProc\fR;
    Tcl_FSFreeInternalRepProc *\fIfreeInternalRepProc\fR;
    Tcl_FSInternalToNormalizedProc *\fIinternalToNormalizedProc\fR;
    Tcl_FSCreateInternalRepProc *\fIcreateInternalRepProc\fR;
    Tcl_FSNormalizePathProc *\fInormalizePathProc\fR;
    Tcl_FSFilesystemPathTypeProc *\fIfilesystemPathTypeProc\fR;
    Tcl_FSFilesystemSeparatorProc *\fIfilesystemSeparatorProc\fR;
    Tcl_FSStatProc *\fIstatProc\fR;
    Tcl_FSAccessProc *\fIaccessProc\fR;
    Tcl_FSOpenFileChannelProc *\fIopenFileChannelProc\fR;
    Tcl_FSMatchInDirectoryProc *\fImatchInDirectoryProc\fR;
    Tcl_FSUtimeProc *\fIutimeProc\fR;
    Tcl_FSLinkProc *\fIlinkProc\fR;
    Tcl_FSListVolumesProc *\fIlistVolumesProc\fR;
    Tcl_FSFileAttrStringsProc *\fIfileAttrStringsProc\fR;
    Tcl_FSFileAttrsGetProc *\fIfileAttrsGetProc\fR;
    Tcl_FSFileAttrsSetProc *\fIfileAttrsSetProc\fR;
    Tcl_FSCreateDirectoryProc *\fIcreateDirectoryProc\fR;
    Tcl_FSRemoveDirectoryProc *\fIremoveDirectoryProc\fR;
    Tcl_FSDeleteFileProc *\fIdeleteFileProc\fR;
    Tcl_FSCopyFileProc *\fIcopyFileProc\fR;
    Tcl_FSRenameFileProc *\fIrenameFileProc\fR;
    Tcl_FSCopyDirectoryProc *\fIcopyDirectoryProc\fR;
    Tcl_FSLstatProc *\fIlstatProc\fR;
    Tcl_FSLoadFileProc *\fIloadFileProc\fR;
    Tcl_FSGetCwdProc *\fIgetCwdProc\fR;
    Tcl_FSChdirProc *\fIchdirProc\fR;
} Tcl_Filesystem;
.CE
.PP
Except for the first three fields in this structure which contain
simple data elements, all entries contain addresses of functions called
by the generic filesystem layer to perform the complete range of
filesystem related actions.
.PP
The many functions in this structure are broken down into three
categories: infrastructure functions (almost all of which must be
implemented), operational functions (which must be implemented if a
complete filesystem is provided), and efficiency functions (which need
only be implemented if they can be done so efficiently, or if they have
side-effects which are required by the filesystem; Tcl has less
efficient emulations it can fall back on).  It is important to note
that, in the current version of Tcl, most of these fallbacks are only
used to handle commands initiated in Tcl, not in C. What this means is,
that if a \fBfile rename\fR command is issued in Tcl, and the relevant
filesystem(s) do not implement their \fITcl_FSRenameFileProc\fR, Tcl's
core will instead fallback on a combination of other filesystem
functions (it will use \fITcl_FSCopyFileProc\fR followed by
\fITcl_FSDeleteFileProc\fR, and if \fITcl_FSCopyFileProc\fR is not
implemented there is a further fallback).  However, if a
\fITcl_FSRenameFileProc\fR command is issued at the C level, no such
fallbacks occur.  This is true except for the last four entries in the
filesystem table (\fBlstat\fR, \fBload\fR, \fBgetcwd\fR and \fBchdir\fR)
for which fallbacks do in fact occur at the C level.
.PP
Any functions which take path names in Tcl_Obj form take
those names in UTF\-8 form.  The filesystem infrastructure API is
designed to support efficient, cached conversion of these UTF\-8 paths
to other native representations.
.SS "EXAMPLE FILESYSTEM DEFINITION"
.PP
Here is the filesystem lookup table used by the
.QW vfs
extension which allows filesystem actions to be implemented in Tcl.
.CS
static Tcl_Filesystem vfsFilesystem = {
    "tclvfs",
    sizeof(Tcl_Filesystem),
    TCL_FILESYSTEM_VERSION_1,
    &VfsPathInFilesystem,
    &VfsDupInternalRep,
    &VfsFreeInternalRep,
    /* No internal to normalized, since we don't create
     * any pure 'internal' Tcl_Obj path representations */
    NULL,
    /* No create native rep function, since we don't use
     * it and don't choose to support uses of
     * Tcl_FSNewNativePath */
    NULL,
    /* Normalize path isn't needed - we assume paths only
     * have one representation */
    NULL,
    &VfsFilesystemPathType,
    &VfsFilesystemSeparator,
    &VfsStat,
    &VfsAccess,
    &VfsOpenFileChannel,
    &VfsMatchInDirectory,
    &VfsUtime,
    /* We choose not to support symbolic links inside our
     * VFS's */
    NULL,
    &VfsListVolumes,
    &VfsFileAttrStrings,
    &VfsFileAttrsGet,
    &VfsFileAttrsSet,
    &VfsCreateDirectory,
    &VfsRemoveDirectory,
    &VfsDeleteFile,
    /* No copy file; use the core fallback mechanism */
    NULL,
    /* No rename file; use the core fallback mechanism */
    NULL,
    /* No copy directory; use the core fallback mechanism */
    NULL,
    /* Core will use stat for lstat */
    NULL,
    /* No load; use the core fallback mechanism */
    NULL,
    /* We don't need a getcwd or chdir; the core's own
     * internal value is suitable */
    NULL,
    NULL
};
.CE
.SH "FILESYSTEM INFRASTRUCTURE"
.PP
These fields contain basic information about the filesystem structure
and addresses of functions which are used to associate
a particular filesystem with a file path, and deal with the internal
handling of path representations, for example copying and freeing such
representations.
.SS TYPENAME
.PP
The \fItypeName\fR field contains a null-terminated string that
identifies the type of the filesystem implemented, e.g.
.QW native ,
.QW zip
or
.QW vfs .
.SS "STRUCTURE LENGTH"
.PP
The \fIstructureLength\fR field is generally implemented as
\fIsizeof(Tcl_Filesystem)\fR, and is there to allow easier
binary backwards compatibility if the size of the structure
changes in a future Tcl release.
.SS VERSION
.PP
The \fIversion\fR field should be set to \fBTCL_FILESYSTEM_VERSION_1\fR.
.SS PATHINFILESYSTEMPROC
.PP
The \fIpathInFilesystemProc\fR field contains the address of a function
which is called to determine whether a given path object belongs to this
filesystem or not.  Tcl will only call the rest of the filesystem
functions with a path for which this function has returned \fBTCL_OK\fR.
If the path does not belong, -1 should be returned (the behaviour of Tcl
for any other return value is not defined).  If \fBTCL_OK\fR is returned,
then the optional \fIclientDataPtr\fR output parameter can be used to
return an internal (filesystem specific) representation of the path,
which will be cached inside the path object, and may be retrieved
efficiently by the other filesystem functions.  Tcl will simultaneously
cache the fact that this path belongs to this filesystem.  Such caches
are invalidated when filesystem structures are added or removed from
Tcl's internal list of known filesystems.
.PP
.CS
typedef int Tcl_FSPathInFilesystemProc(
        Tcl_Obj *\fIpathPtr\fR,
        ClientData *\fIclientDataPtr\fR);
.CE
.SS DUPINTERNALREPPROC
.PP
This function makes a copy of a path's internal representation, and is
called when Tcl needs to duplicate a path object.  If NULL, Tcl will
simply not copy the internal representation, which may then need to be
regenerated later.
.PP
.CS
typedef ClientData Tcl_FSDupInternalRepProc(
        ClientData \fIclientData\fR);
.CE
.SS FREEINTERNALREPPROC
Free the internal representation.  This must be implemented if internal
representations need freeing (i.e. if some memory is allocated when an
internal representation is generated), but may otherwise be NULL.
.PP
.CS
typedef void Tcl_FSFreeInternalRepProc(
        ClientData \fIclientData\fR);
.CE
.SS INTERNALTONORMALIZEDPROC
.PP
Function to convert internal representation to a normalized path.  Only
required if the filesystem creates pure path objects with no string/path
representation.  The return value is a Tcl object whose string
representation is the normalized path.
.PP
.CS
typedef Tcl_Obj* Tcl_FSInternalToNormalizedProc(
        ClientData \fIclientData\fR);
.CE
.SS CREATEINTERNALREPPROC
.PP
Function to take a path object, and calculate an internal
representation for it, and store that native representation in the
object.  May be NULL if paths have no internal representation, or if
the \fITcl_FSPathInFilesystemProc\fR for this filesystem always
immediately creates an internal representation for paths it accepts.
.PP
.CS
typedef ClientData Tcl_FSCreateInternalRepProc(
        Tcl_Obj *\fIpathPtr\fR);
.CE
.SS NORMALIZEPATHPROC
.PP
Function to normalize a path.  Should be implemented for all
filesystems which can have multiple string representations for the same
path object.  In Tcl, every
.QW path
must have a single unique
.QW normalized
string representation.  Depending on the filesystem,
there may be more than one unnormalized string representation which
refers to that path (e.g. a relative path, a path with different
character case if the filesystem is case insensitive, a path contain a
reference to a home directory such as
.QW ~ ,
a path containing symbolic
links, etc).  If the very last component in the path is a symbolic
link, it should not be converted into the object it points to (but
its case or other aspects should be made unique).  All other path
components should be converted from symbolic links.  This one
exception is required to agree with Tcl's semantics with \fBfile
delete\fR, \fBfile rename\fR, \fBfile copy\fR operating on symbolic links.
This function may be called with \fInextCheckpoint\fR either
at the beginning of the path (i.e. zero), at the end of the path, or
at any intermediate file separator in the path.  It will never
point to any other arbitrary position in the path. In the last of
the three valid cases, the implementation can assume that the path
up to and including the file separator is known and normalized.
.PP
.CS
typedef int Tcl_FSNormalizePathProc(
        Tcl_Interp *\fIinterp\fR,
        Tcl_Obj *\fIpathPtr\fR,
        int \fInextCheckpoint\fR);
.CE
.SH "FILESYSTEM OPERATIONS"
.PP
The fields in this section of the structure contain addresses of
functions which are called to carry out the basic filesystem
operations.  A filesystem which expects to be used with the complete
standard Tcl command set must implement all of these.  If some of
them are not implemented, then certain Tcl commands may fail when
operating on paths within that filesystem.  However, in some instances
this may be desirable (for example, a read-only filesystem should not
implement the last four functions, and a filesystem which does not
support symbolic links need not implement the \fBreadlink\fR function,
etc.  The Tcl core expects filesystems to behave in this way).
.SS FILESYSTEMPATHTYPEPROC
.PP
Function to determine the type of a path in this filesystem.  May be
NULL, in which case no type information will be available to users of
the filesystem.  The
.QW type
is used only for informational purposes,
and should be returned as the string representation of the Tcl_Obj
which is returned.  A typical return value might be
.QW networked ,
.QW zip
or
.QW ftp .
The Tcl_Obj result is owned by the filesystem and so Tcl will
increment the refCount of that object if it wishes to retain a reference
to it.
.PP
.CS
typedef Tcl_Obj* Tcl_FSFilesystemPathTypeProc(
        Tcl_Obj *\fIpathPtr\fR);
.CE
.SS FILESYSTEMSEPARATORPROC
.PP
Function to return the separator character(s) for this filesystem.
This need only be implemented if the filesystem wishes to use a
different separator than the standard string
.QW / .
Amongst other
uses, it is returned by the \fBfile separator\fR command.  The
return value should be an object with refCount of zero.
.PP
.CS
typedef Tcl_Obj* Tcl_FSFilesystemSeparatorProc(
        Tcl_Obj *\fIpathPtr\fR);
.CE
.SS STATPROC
.PP
Function to process a \fBTcl_FSStat\fR call.  Must be implemented for any
reasonable filesystem, since many Tcl level commands depend crucially
upon it (e.g. \fBfile atime\fR, \fBfile isdirectory\fR, \fBfile size\fR,
\fBglob\fR).
.PP
.CS
typedef int Tcl_FSStatProc(
        Tcl_Obj *\fIpathPtr\fR,
        Tcl_StatBuf *\fIstatPtr\fR);
.CE
.PP
The \fBTcl_FSStatProc\fR fills the stat structure \fIstatPtr\fR with
information about the specified file.  You do not need any access
rights to the file to get this information but you need search rights
to all directories named in the path leading to the file.  The stat
structure includes info regarding device, inode (always 0 on Windows),
privilege mode, nlink (always 1 on Windows), user id (always 0 on
Windows), group id (always 0 on Windows), rdev (same as device on
Windows), size, last access time, last modification time, and
last metadata change time.
.PP
If the file represented by \fIpathPtr\fR exists, the
\fBTcl_FSStatProc\fR returns 0 and the stat structure is filled with
data.  Otherwise, -1 is returned, and no stat info is given.
.SS ACCESSPROC
.PP
Function to process a \fBTcl_FSAccess\fR call.  Must be implemented for
any reasonable filesystem, since many Tcl level commands depend crucially
upon it (e.g. \fBfile exists\fR, \fBfile readable\fR).
.PP
.CS
typedef int Tcl_FSAccessProc(
        Tcl_Obj *\fIpathPtr\fR,
        int \fImode\fR);
.CE
.PP
The \fBTcl_FSAccessProc\fR checks whether the process would be allowed
to read, write or test for existence of the file (or other filesystem
object) whose name is in \fIpathPtr\fR.  If the pathname refers to a
symbolic link, then the
permissions of the file referred by this symbolic link should be tested.
.PP
On success (all requested permissions granted), zero is returned.  On
error (at least one bit in mode asked for a permission that is denied,
or some other  error occurred), -1 is returned.
.SS OPENFILECHANNELPROC
.PP
Function to process a \fBTcl_FSOpenFileChannel\fR call.  Must be
implemented for any reasonable filesystem, since any operations
which require open or accessing a file's contents will use it
(e.g. \fBopen\fR, \fBencoding\fR, and many Tk commands).
.PP
.CS
typedef Tcl_Channel Tcl_FSOpenFileChannelProc(
        Tcl_Interp *\fIinterp\fR,
        Tcl_Obj *\fIpathPtr\fR,
        int \fImode\fR,
        int \fIpermissions\fR);
.CE
.PP
The \fBTcl_FSOpenFileChannelProc\fR opens a file specified by
\fIpathPtr\fR and returns a channel handle that can be used to perform
input and output on the file.  This API is modeled after the \fBfopen\fR
procedure of the Unix standard I/O library.  The syntax and meaning of
all arguments is similar to those given in the Tcl \fBopen\fR command
when opening a file, where the \fImode\fR argument is a combination of
the POSIX flags O_RDONLY, O_WRONLY, etc.  If an error occurs while
opening the channel, the \fBTcl_FSOpenFileChannelProc\fR returns NULL and
records a POSIX error code that can be retrieved with \fBTcl_GetErrno\fR.
In addition, if \fIinterp\fR is non-NULL, the
\fBTcl_FSOpenFileChannelProc\fR leaves an error message in \fIinterp\fR's
result after any error.
.PP
The newly created channel must not registered in the supplied
interpreter; that task is up to the caller of
\fBTcl_FSOpenFileChannel\fR (if necessary). If one of
the standard channels, \fBstdin, stdout\fR or \fBstderr\fR was
previously closed, the act of creating the new channel also assigns it
as a replacement for the standard channel.
.SS MATCHINDIRECTORYPROC
.PP
Function to process a \fBTcl_FSMatchInDirectory\fR call.  If not
implemented, then glob and recursive copy functionality will be lacking
in the filesystem (and this may impact commands like \fBencoding names\fR
which use glob functionality internally).
.PP
.CS
typedef int Tcl_FSMatchInDirectoryProc(
        Tcl_Interp* \fIinterp\fR,
        Tcl_Obj *\fIresultPtr\fR,
        Tcl_Obj *\fIpathPtr\fR,
        const char *\fIpattern\fR,
        Tcl_GlobTypeData *\fItypes\fR);
.CE
.PP
The function should return all files or directories (or other filesystem
objects) which match the given pattern and accord with the \fItypes\fR
specification given.  There are two ways in which this function may be
called.  If \fIpattern\fR is NULL, then \fIpathPtr\fR is a full path
specification of a single file or directory which should be checked for
existence and correct type.  Otherwise, \fIpathPtr\fR is a directory, the
contents of which the function should search for files or directories
which have the correct type.  In either case, \fIpathPtr\fR can be
assumed to be both non-NULL and non-empty.  It is not currently
documented whether \fIpathPtr\fR will have a file separator at its end of
not, so code should be flexible to both possibilities.
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the matching process.  Error messages are placed in
\fIinterp\fR, unless \fIinterp\fR in NULL in which case no error
message need be generated; on a \fBTCL_OK\fR result, results should be 
added to the \fIresultPtr\fR object given (which can be assumed to be a 
valid unshared Tcl list).  The matches added
to \fIresultPtr\fR should include any path prefix given in \fIpathPtr\fR
(this usually means they will be absolute path specifications).
Note that if no matches are found, that simply leads to an empty
result; errors are only signaled for actual file or filesystem
problems which may occur during the matching process.
.PP
The \fBTcl_GlobTypeData\fR structure passed in the \fItypes\fR 
parameter contains the following fields:
.CS
typedef struct Tcl_GlobTypeData {
        /* Corresponds to bcdpfls as in 'find -t' */
        int \fItype\fR;
        /* Corresponds to file permissions */
        int \fIperm\fR;
        /* Acceptable mac type */
        Tcl_Obj *\fImacType\fR;
        /* Acceptable mac creator */
        Tcl_Obj *\fImacCreator\fR;
} Tcl_GlobTypeData;
.CE
.PP
There are two specific cases which it is important to handle correctly,
both when \fItypes\fR is non-NULL. The two cases are when \fItypes->types
& TCL_GLOB_TYPE_DIR\fR or \fItypes->types & TCL_GLOB_TYPE_MOUNT\fR are
true (and in particular when the other flags are false).  In the first of
these cases, the function must list the contained directories.  Tcl uses
this to implement recursive globbing, so it is critical that filesystems
implement directory matching correctly.  In the second of these cases,
with \fBTCL_GLOB_TYPE_MOUNT\fR, the filesystem must list the mount points
which lie within the given \fIpathPtr\fR (and in this case, \fIpathPtr\fR
need not lie within the same filesystem - different to all other cases in
which this function is called).  Support for this is critical if Tcl is
to have seamless transitions between from one filesystem to another.
.SS UTIMEPROC
.PP
Function to process a \fBTcl_FSUtime\fR call.  Required to allow setting
(not reading) of times with \fBfile mtime\fR, \fBfile atime\fR and the
open-r/open-w/fcopy implementation of \fBfile copy\fR.
.PP
.CS
typedef int Tcl_FSUtimeProc(
        Tcl_Obj *\fIpathPtr\fR,
        struct utimbuf *\fItval\fR);
.CE
.PP
The access and modification times of the file specified by \fIpathPtr\fR
should be changed to the values given in the \fItval\fR structure.
.PP
The return value should be 0 on success and -1 on an error, as
with the system \fButime\fR.
.SS LINKPROC
.PP
Function to process a \fBTcl_FSLink\fR call.  Should be implemented
only if the filesystem supports links, and may otherwise be NULL.
.PP
.CS
typedef Tcl_Obj* Tcl_FSLinkProc(
        Tcl_Obj *\fIlinkNamePtr\fR,
        Tcl_Obj *\fItoPtr\fR,
        int \fIlinkAction\fR);
.CE
.PP
If \fItoPtr\fR is NULL, the function is being asked to read the
contents of a link.  The result is a Tcl_Obj specifying the contents of
the link given by \fIlinkNamePtr\fR, or NULL if the link could
not be read.  The result is owned by the caller (and should therefore
have its ref count incremented before being returned).  Any callers
should call Tcl_DecrRefCount on this result when it is no longer needed.
If \fItoPtr\fR is not NULL, the function should attempt to create a link.
The result in this case should be \fItoPtr\fR if the link was successful
and NULL otherwise.  In this case the result is not owned by the caller
(i.e. no ref count manipulation on either end is needed). See
the documentation for \fBTcl_FSLink\fR for the correct interpretation
of the \fIlinkAction\fR flags.
.SS LISTVOLUMESPROC
.PP
Function to list any filesystem volumes added by this filesystem.
Should be implemented only if the filesystem adds volumes at the head
of the filesystem, so that they can be returned by \fBfile volumes\fR.
.PP
.CS
typedef Tcl_Obj* Tcl_FSListVolumesProc(void);
.CE
.PP
The result should be a list of volumes added by this filesystem, or
NULL (or an empty list) if no volumes are provided.  The result object
is considered to be owned by the filesystem (not by Tcl's core), but
should be given a refCount for Tcl.  Tcl will use the contents of the
list and then decrement that refCount.  This allows filesystems to
choose whether they actually want to retain a
.QW "master list"
of volumes
or not (if not, they generate the list on the fly and pass it to Tcl
with a refCount of 1 and then forget about the list, if yes, then
they simply increment the refCount of their master list and pass it
to Tcl which will copy the contents and then decrement the count back
to where it was).
.PP
Therefore, Tcl considers return values from this proc to be read-only.
.SS FILEATTRSTRINGSPROC
.PP
Function to list all attribute strings which are valid for this
filesystem.  If not implemented the filesystem will not support
the \fBfile attributes\fR command.  This allows arbitrary additional
information to be attached to files in the filesystem.  If it is
not implemented, there is no need to implement the \fBget\fR and \fBset\fR
methods.
.PP
.CS
typedef const char** Tcl_FSFileAttrStringsProc(
        Tcl_Obj *\fIpathPtr\fR,
        Tcl_Obj** \fIobjPtrRef\fR);
.CE
.PP
The called function may either return an array of strings, or may
instead return NULL and place a Tcl list into the given \fIobjPtrRef\fR.  Tcl
will take that list and first increment its reference count before using it.
On completion of that use, Tcl will decrement its reference count.  Hence if
the list should be disposed of by Tcl when done, it should have a
reference count of zero, and if the list should not be disposed of, the
filesystem should ensure it returns an object with a reference count
of at least one.
.SS FILEATTRSGETPROC
.PP
Function to process a \fBTcl_FSFileAttrsGet\fR call, used by \fBfile
attributes\fR.
.PP
.CS
typedef int Tcl_FSFileAttrsGetProc(
        Tcl_Interp *\fIinterp\fR,
        int \fIindex\fR,
        Tcl_Obj *\fIpathPtr\fR,
        Tcl_Obj **\fIobjPtrRef\fR);
.CE
.PP
Returns a standard Tcl return code.  The attribute value retrieved,
which corresponds to the \fIindex\fR'th element in the list returned by
the \fBTcl_FSFileAttrStringsProc\fR, is a Tcl_Obj placed in \fIobjPtrRef\fR (if
\fBTCL_OK\fR was returned) and is likely to have a reference count of zero.  Either
way we must either store it somewhere (e.g. the Tcl result), or
Incr/Decr its reference count to ensure it is properly freed.
.SS FILEATTRSSETPROC
.PP
Function to process a \fBTcl_FSFileAttrsSet\fR call, used by \fBfile
attributes\fR.  If the filesystem is read-only, there is no need
to implement this.
.PP
.CS
typedef int Tcl_FSFileAttrsSetProc(
        Tcl_Interp *\fIinterp\fR,
        int \fIindex\fR,
        Tcl_Obj *\fIpathPtr\fR,
        Tcl_Obj *\fIobjPtr\fR);
.CE
.PP
The attribute value of the \fIindex\fR'th element in the list returned by
the Tcl_FSFileAttrStringsProc should be set to the \fIobjPtr\fR given.
.SS CREATEDIRECTORYPROC
.PP
Function to process a \fBTcl_FSCreateDirectory\fR call.  Should be
implemented unless the FS is read-only.
.PP
.CS
typedef int Tcl_FSCreateDirectoryProc(
        Tcl_Obj *\fIpathPtr\fR);
.CE
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the process.  If successful, a new directory should have
been added to the filesystem in the location specified by
\fIpathPtr\fR.
.SS REMOVEDIRECTORYPROC
.PP
Function to process a \fBTcl_FSRemoveDirectory\fR call.  Should be
implemented unless the FS is read-only.
.PP
.CS
typedef int Tcl_FSRemoveDirectoryProc(
        Tcl_Obj *\fIpathPtr\fR,
        int \fIrecursive\fR,
        Tcl_Obj **\fIerrorPtr\fR);
.CE
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the process.  If successful, the directory specified by
\fIpathPtr\fR should have been removed from the filesystem.  If the
\fIrecursive\fR flag is given, then a non-empty directory should be
deleted without error.  If this flag is not given, then and the
directory is non-empty a POSIX
.QW EEXIST
error should be signaled.  If an
error does occur, the name of the file or directory which caused the
error should be placed in \fIerrorPtr\fR.
.SS DELETEFILEPROC
.PP
Function to process a \fBTcl_FSDeleteFile\fR call.  Should be implemented
unless the FS is read-only.
.PP
.CS
typedef int Tcl_FSDeleteFileProc(
        Tcl_Obj *\fIpathPtr\fR);
.CE
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the process.  If successful, the file specified by
\fIpathPtr\fR should have been removed from the filesystem.  Note that,
if the filesystem supports symbolic links, Tcl will always call this
function and not Tcl_FSRemoveDirectoryProc when needed to delete them
(even if they are symbolic links to directories).
.SH "FILESYSTEM EFFICIENCY"
.PP
These functions need not be implemented for a particular filesystem
because the core has a fallback implementation available. See each
individual description for the consequences of leaving the field NULL.
.SS LSTATPROC
.PP
Function to process a \fBTcl_FSLstat\fR call.  If not implemented, Tcl
will attempt to use the \fIstatProc\fR defined above instead.  Therefore
it need only be implemented if a filesystem can differentiate between
\fBstat\fR and \fBlstat\fR calls.
.PP
.CS
typedef int Tcl_FSLstatProc(
        Tcl_Obj *\fIpathPtr\fR,
        Tcl_StatBuf *\fIstatPtr\fR);
.CE
.PP
The behavior of this function is very similar to that of the
\fBTcl_FSStatProc\fR defined above, except that if it is applied
to a symbolic link, it returns information about the link, not
about the target file.
.SS COPYFILEPROC
.PP
Function to process a \fBTcl_FSCopyFile\fR call.  If not implemented Tcl
will fall back on \fBopen\fR-r, \fBopen\fR-w and \fBfcopy\fR as a
copying mechanism.
Therefore it need only be implemented if the filesystem can perform
that action more efficiently.
.PP
.CS
typedef int Tcl_FSCopyFileProc(
        Tcl_Obj *\fIsrcPathPtr\fR,
        Tcl_Obj *\fIdestPathPtr\fR);
.CE
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the copying process.  Note that, \fIdestPathPtr\fR is the
name of the file which should become the copy of \fIsrcPathPtr\fR. It
is never the name of a directory into which \fIsrcPathPtr\fR could be
copied (i.e. the function is much simpler than the Tcl level \fBfile
copy\fR subcommand).  Note that,
if the filesystem supports symbolic links, Tcl will always call this
function and not \fIcopyDirectoryProc\fR when needed to copy them
(even if they are symbolic links to directories).  Finally, if the
filesystem determines it cannot support the \fBfile copy\fR action,
calling \fBTcl_SetErrno(EXDEV)\fR and returning a non-\fBTCL_OK\fR
result will tell Tcl to use its standard fallback mechanisms.
.SS RENAMEFILEPROC
.PP
Function to process a \fBTcl_FSRenameFile\fR call.  If not implemented,
Tcl will fall back on a copy and delete mechanism.  Therefore it need
only be implemented if the filesystem can perform that action more
efficiently.
.PP
.CS
typedef int Tcl_FSRenameFileProc(
        Tcl_Obj *\fIsrcPathPtr\fR,
        Tcl_Obj *\fIdestPathPtr\fR);
.CE
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the renaming process.  If the
filesystem determines it cannot support the \fBfile rename\fR action,
calling \fBTcl_SetErrno(EXDEV)\fR and returning a non-\fBTCL_OK\fR
result will tell Tcl to use its standard fallback mechanisms.
.SS COPYDIRECTORYPROC
.PP
Function to process a \fBTcl_FSCopyDirectory\fR call.  If not
implemented, Tcl will fall back on a recursive \fBfile mkdir\fR, \fBfile copy\fR
mechanism.  Therefore it need only be implemented if the filesystem can
perform that action more efficiently.
.PP
.CS
typedef int Tcl_FSCopyDirectoryProc(
        Tcl_Obj *\fIsrcPathPtr\fR,
        Tcl_Obj *\fIdestPathPtr\fR,
        Tcl_Obj **\fIerrorPtr\fR);
.CE
.PP
The return value is a standard Tcl result indicating whether an error
occurred in the copying process.  If an error does occur, the name of
the file or directory which caused the error should be placed in
\fIerrorPtr\fR. Note that, \fIdestPathPtr\fR is the name of the
directory-name which should become the mirror-image of
\fIsrcPathPtr\fR. It is not the name of a directory into which
\fIsrcPathPtr\fR should be copied (i.e. the function is much simpler
than the Tcl level \fBfile copy\fR subcommand).  Finally, if the
filesystem determines it cannot support the directory copy action,
calling \fBTcl_SetErrno(EXDEV)\fR and returning a non-\fBTCL_OK\fR
result will tell Tcl to use its standard fallback mechanisms.
.SS LOADFILEPROC
.PP
Function to process a \fBTcl_FSLoadFile\fR call.  If not implemented, Tcl
will fall back on a copy to native-temp followed by a \fBTcl_FSLoadFile\fR on
that temporary copy.  Therefore it need only be implemented if the
filesystem can load code directly, or it can be implemented simply to
return \fBTCL_ERROR\fR to disable load functionality in this filesystem
entirely.
.PP
.CS
typedef int Tcl_FSLoadFileProc(
        Tcl_Interp *\fIinterp\fR,
        Tcl_Obj *\fIpathPtr\fR,
        Tcl_LoadHandle *\fIhandlePtr\fR,
        Tcl_FSUnloadFileProc *\fIunloadProcPtr\fR);
.CE
.PP
Returns a standard Tcl completion code.  If an error occurs, an error
message is left in the \fIinterp\fR's result.  The function dynamically loads a
binary code file into memory.  On a successful load, the \fIhandlePtr\fR
should be filled with a token for the dynamically loaded file, and the
\fIunloadProcPtr\fR should be filled in with the address of a procedure.
The unload procedure will be called with the given \fBTcl_LoadHandle\fR as its
only parameter when Tcl needs to unload the file.  For example, for the
native filesystem, the \fBTcl_LoadHandle\fR returned is currently a token
which can be used in the private \fBTclpFindSymbol\fR to access functions
in the new code.  Each filesystem is free to define the
\fBTcl_LoadHandle\fR as it requires.  Finally, if the
filesystem determines it cannot support the file load action,
calling \fBTcl_SetErrno(EXDEV)\fR and returning a non-\fBTCL_OK\fR
result will tell Tcl to use its standard fallback mechanisms.
.SS UNLOADFILEPROC
.PP
Function to unload a previously successfully loaded file.  If load was
implemented, then this should also be implemented, if there is any
cleanup action required.
.PP
.CS
typedef void Tcl_FSUnloadFileProc(
        Tcl_LoadHandle \fIloadHandle\fR);
.CE
.SS GETCWDPROC     
.PP
Function to process a \fBTcl_FSGetCwd\fR call.  Most filesystems need not
implement this.  It will usually only be called once, if \fBgetcwd\fR is
called before \fBchdir\fR.  May be NULL.
.PP
.CS
typedef Tcl_Obj* Tcl_FSGetCwdProc(
        Tcl_Interp *\fIinterp\fR);
.CE
.PP
If the filesystem supports a native notion of a current working
directory (which might perhaps change independent of Tcl), this
function should return that cwd as the result, or NULL if the current
directory could not be determined (e.g. the user does not have
appropriate permissions on the cwd directory).  If NULL is returned, an
error message is left in the \fIinterp\fR's result.
.SS CHDIRPROC
.PP
Function to process a \fBTcl_FSChdir\fR call.  If filesystems do not
implement this, it will be emulated by a series of directory access
checks.  Otherwise, virtual filesystems which do implement it need only
respond with a positive return result if the \fIpathPtr\fR is a valid,
accessible directory in their filesystem.  They need not remember the
result, since that will be automatically remembered for use by
\fBTcl_FSGetCwd\fR.
Real filesystems should carry out the correct action (i.e. call the
correct system \fBchdir\fR API).
.PP
.CS
typedef int Tcl_FSChdirProc(
        Tcl_Obj *\fIpathPtr\fR);
.CE
.PP
The \fBTcl_FSChdirProc\fR changes the applications current working
directory to the value specified in \fIpathPtr\fR. The function returns
-1 on error or 0 on success.
.SH "SEE ALSO"
cd(n), file(n), load(n), open(n), pwd(n), unload(n)
.SH KEYWORDS
stat, access, filesystem, vfs, virtual