path: root/src/H5FDgass.c

/*
 * Copyright © 1999-2001 NCSA
 *                       All rights reserved.
 *
 * Programmer:  Saurabh Bagchi (bagchi@uiuc.edu)
 *              Thursday, August 12 -Tuesday, August 17, 1999
 *
 * Purpose:	This is the GASS I/O driver.
 *
 */
#include "H5private.h"		/*library functions			*/
#include "H5Eprivate.h"		/*error handling			*/
#include "H5Fprivate.h"		/*files					*/
#include "H5FDprivate.h"	/*file driver				  */
#include "H5FDgass.h"           /* Core file driver */
#include "H5Iprivate.h"		/*object IDs				  */
#include "H5MMprivate.h"        /* Memory allocation */
#include "H5Pprivate.h"		/*property lists			*/


#undef MAX
#define MAX(X,Y)	((X)>(Y)?(X):(Y))

/* The driver identification number, initialized at runtime */
static hid_t H5FD_GASS_g = 0;

#ifdef H5_HAVE_GASS

/* File operations */
#define OP_UNKNOWN	0
#define OP_READ		1
#define OP_WRITE	2

/*
 * The description of a file belonging to this driver. The `eoa' and `eof'
 * determine the amount of hdf5 address space in use and the high-water mark
 * of the file (the current size of the underlying Unix file). The `pos'
 * value is used to eliminate file position updates when they would be a
 * no-op. Unfortunately we've found systems that use separate file position
 * indicators for reading and writing so the lseek can only be eliminated if
 * the current operation is the same as the previous operation.  When opening
 * a file the `eof' will be set to the current file size, `eoa' will be set
 * to zero, `pos' will be set to H5F_ADDR_UNDEF (as it is when an error
 * occurs), and `op' will be set to H5F_OP_UNKNOWN.
 */
typedef struct H5FD_gass_t {
    H5FD_t	pub;			/*public stuff, must be first	*/
    int		fd;			/*the unix file			*/
    GASS_Info   info;                   /*file information */
    haddr_t	eoa;			/*end of allocated region	*/
    haddr_t	eof;			/*end of file; current file size*/
    haddr_t	pos;			/*current file I/O position	*/
    int		op;			/*last operation		*/
    
  
} H5FD_gass_t;

/*
 * This driver supports systems that have the lseek64() function by defining
 * some macros here so we don't have to have conditional compilations later
 * throughout the code.
 *
 * file_offset_t:	The datatype for file offsets, the second argument of
 *			the lseek() or lseek64() call.
 *
 * file_seek:		The function which adjusts the current file position,
 *			either lseek() or lseek64().
 */
/* adding for windows NT file system support. */

#ifdef H5_HAVE_LSEEK64
#   define file_offset_t	off64_t
#   define file_seek		lseek64
#elif defined (WIN32)
#   ifdef __MWERKS__
#       define file_offset_t off_t
#       define file_seek lseek
#   else /*MSVC*/
#       define file_offset_t __int64
#       define file_seek _lseeki64
#   endif
#else
#   define file_offset_t	off_t
#   define file_seek		lseek
#endif



/*
 * These macros check for overflow of various quantities.  These macros
 * assume that file_offset_t is signed and haddr_t and size_t are unsigned.
 * 
 * ADDR_OVERFLOW:	Checks whether a file address of type `haddr_t'
 *			is too large to be represented by the second argument
 *			of the file seek function.
 *
 * SIZE_OVERFLOW:	Checks whether a buffer size of type `hsize_t' is too
 *			large to be represented by the `size_t' type.
 *
 * REGION_OVERFLOW:	Checks whether an address and size pair describe data
 *			which can be addressed entirely by the second
 *			argument of the file seek function.
 */
#define MAXADDR (((haddr_t)1<<(8*sizeof(file_offset_t)-1))-1)
#define ADDR_OVERFLOW(A)	(HADDR_UNDEF==(A) ||			      \
				 ((A) & ~(haddr_t)MAXADDR))
#define SIZE_OVERFLOW(Z)	((Z) & ~(hsize_t)MAXADDR)
#define REGION_OVERFLOW(A,Z)	(ADDR_OVERFLOW(A) || SIZE_OVERFLOW(Z) ||      \
				 sizeof(file_offset_t)<sizeof(size_t) ||      \
                                 HADDR_UNDEF==(A)+(Z) ||		      \
				 (file_offset_t)((A)+(Z))<(file_offset_t)(A))

/* Prototypes */
static H5FD_t *H5FD_gass_open(const char *name, unsigned flags, hid_t fapl_id,
			      haddr_t maxaddr);
static herr_t H5FD_gass_close(H5FD_t *_file);
static herr_t H5FD_gass_query(const H5FD_t *_f1, unsigned long *flags);
static haddr_t H5FD_gass_get_eoa(H5FD_t *_file);
static herr_t H5FD_gass_set_eoa(H5FD_t *_file, haddr_t addr);
static haddr_t H5FD_gass_get_eof(H5FD_t *_file);
static herr_t H5FD_gass_read(H5FD_t *_file, H5FD_mem_t type, hid_t fapl_id, haddr_t addr,
			     size_t size, void *buf);
static herr_t H5FD_gass_write(H5FD_t *_file, H5FD_mem_t type, hid_t fapl_id, haddr_t addr,
			      size_t size, const void *buf);

/* GASS I/O-specific file access properties */
typedef struct H5FD_gass_fapl_t {
  GASS_Info            info;      /* access property parameters */
} H5FD_gass_fapl_t;

/* The GASS IO driver information */
static const H5FD_class_t H5FD_gass_g = {
    "gass",					/*name			*/
    MAXADDR,					/*maxaddr		*/
    H5F_CLOSE_WEAK,				/* fc_degree		*/
    NULL,					/*sb_size		*/
    NULL,					/*sb_encode		*/
    NULL,					/*sb_decode		*/
    sizeof(H5FD_gass_fapl_t), 			/*fapl_size		*/
    NULL,					/*fapl_get		*/
    NULL,					/*fapl_copy		*/
    NULL, 					/*fapl_free		*/
    0,						/*dxpl_size		*/
    NULL,					/*dxpl_copy		*/
    NULL,					/*dxpl_free		*/
    H5FD_gass_open,				/*open			*/
    H5FD_gass_close,				/*close			*/
    NULL,				        /*cmp			*/
    H5FD_gass_query,				/*query			*/
    NULL,					/*alloc			*/
    NULL,					/*free			*/
    H5FD_gass_get_eoa,				/*get_eoa		*/
    H5FD_gass_set_eoa, 				/*set_eoa		*/
    H5FD_gass_get_eof,				/*get_eof		*/
    H5FD_gass_read,				/*read			*/
    H5FD_gass_write,				/*write			*/
    NULL,				        /*flush			*/
    H5FD_FLMAP_SINGLE,				/*fl_map		*/
};

/* Interface initialization */
#define PABLO_MASK	H5FD_gass_mask
#define INTERFACE_INIT	H5FD_gass_init
static int interface_initialize_g = 0;


/*-------------------------------------------------------------------------
 * Function:	H5FD_gass_init
 *
 * Purpose:	Initialize this driver by registering the driver with the
 *		library.
 *
 * Return:	Success:	The driver ID for the gass driver.
 *
 *		Failure:	Negative.
 *
 * Programmer:	Saurabh Bagchi
 *              Friday, August 13, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
hid_t
H5FD_gass_init(void)
{
    FUNC_ENTER(H5FD_gass_init, FAIL);

    if (!H5FD_GASS_g)
        H5FD_GASS_g = H5FDregister(&H5FD_gass_g);

    globus_module_activate (GLOBUS_COMMON_MODULE);
    globus_module_activate (GLOBUS_GASS_FILE_MODULE);

    FUNC_LEAVE(H5FD_GASS_g);
}


/*-------------------------------------------------------------------------
 * Function:	H5Pset_fapl_gass
 *
 * Purpose:	Store the user supplied GASS INFO in
 *		the file access property list FAPL_ID which can then be used
 *		to create and/or open the file. 
 *
 *		GASS info object to be used for file open using GASS.
 *              Any modification to info after
 *		this function call returns may have undetermined effect
 *		to the access property list.  Users should call this
 *		function again to setup the property list.
 *
 *
 * Return:	Success:	Non-negative
 *
 * 		Failure:	Negative
 *
 * Programmer:	Saurabh Bagchi
 *		Friday, August 13, 1999
 *
 * Modifications:
 *
 *		Raymond Lu, 2001-10-25
 *		Changed the file access list to the new generic property list.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5Pset_fapl_gass(hid_t fapl_id, GASS_Info info)
{
    H5FD_gass_fapl_t	fa;
    H5P_genplist_t *plist;      /* Property list pointer */
    herr_t ret_value=FAIL;
    
    FUNC_ENTER(H5Pset_fapl_gass, FAIL);
    /*NO TRACE*/
    
    /* Check arguments */
    if(TRUE!=H5P_isa_class(fapl_id,H5P_FILE_ACCESS) || NULL == (plist = H5I_object(fapl_id)))
        HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list");   

#ifdef LATER
#warning "We need to verify that INFO contain sensible information."
#endif

    /* Initialize driver specific properties */
    fa.info = info;

    ret_value= H5P_set_driver(plist, H5FD_GASS, &fa);

    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5Pget_fapl_gass
 *
 * Purpose:	If the file access property list is set to the H5FD_GASS
 *		driver then this function returns the GASS info object
 *		through the INFO pointer.
 *
 * Return:	Success:	Non-negative with the info object returned 
 *                              through the INFO arguments if non-null. 
 *				The information is copied and it is therefore
 *				valid only until the file access property
 *				list is modified or closed.
 *
 * 		Failure:	Negative
 *
 * Programmer:	Saurabh Bagchi
 *		Friday, August 13, 1999
 *
 * Modifications:
 *
 *              Raymond Lu, 2001-10-25
 *              Changed the file access list to the new generic property list.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5Pget_fapl_gass(hid_t fapl_id, GASS_Info *info/*out*/)
{
    H5FD_gass_fapl_t	*fa;
    H5P_genplist_t *plist;      /* Property list pointer */
    
    FUNC_ENTER(H5Pget_fapl_gass, FAIL);
    H5TRACE2("e","ix",fapl_id,info);

    if(TRUE!=H5P_isa_class(fapl_id,H5P_FILE_ACCESS) || NULL == (plist = H5I_object(fapl_id)))
        HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list");
    if (H5FD_GASS!=H5P_get_driver(plist))
        HRETURN_ERROR(H5E_PLIST, H5E_BADVALUE, FAIL, "incorrect VFL driver");
    if (NULL==(fa=H5P_get_driver_info(plist)))
        HRETURN_ERROR(H5E_PLIST, H5E_BADVALUE, FAIL, "bad VFL driver info");

    if (info)
        *info = fa->info;

    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5FD_gass_open
 *
 * Purpose:	Opens a file with name NAME.  The FLAGS are a bit field with
 *		purpose similar to the second argument of open(2) and which
 *		are defined in H5Fpublic.h. The file access property list
 *		FAPL_ID contains the driver properties and MAXADDR
 *		is the largest address which this file will be expected to
 *		access.
 *
 * Return:	Success:	A pointer to a new file data structure. The
 *				public fields will be initialized by the
 *				caller, which is always H5FD_open().
 *
 *		Failure:	NULL
 *
 * Programmer:	Saurabh Bagchi
 *              Friday, August 13, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static H5FD_t *
H5FD_gass_open(const char *name, unsigned flags, hid_t fapl_id,
	       haddr_t maxaddr)
{
    int		fd;
    H5FD_gass_t	*file=NULL;
    const H5FD_gass_fapl_t	*fa=NULL;
    H5FD_gass_fapl_t		_fa;
    char *filename = (char *) H5MM_malloc(80 * sizeof(char));
    H5P_genplist_t *plist;      /* Property list pointer */
    h5_stat_t sb;
    
    FUNC_ENTER(H5FD_gass_open, NULL);

    /* fprintf(stdout, "Entering H5FD_gass_open name=%s flags=0x%x\n", name, flags); */

    /* Check arguments */
    if (!name || !*name)
        HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, NULL, "invalid file name");
    if (0==maxaddr || HADDR_UNDEF==maxaddr)
        HRETURN_ERROR(H5E_ARGS, H5E_BADRANGE, NULL, "bogus maxaddr");
    if (ADDR_OVERFLOW(maxaddr))
        HRETURN_ERROR(H5E_ARGS, H5E_BADRANGE, NULL, "bogus maxaddr");

    strcpy (filename, name);
    
    /* Obtain a pointer to gass-specific file access properties */
    if(TRUE!=H5P_isa_class(fapl_id,H5P_FILE_ACCESS) || NULL == (plist = H5I_object(fapl_id)))
        HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not a file access property list");
    if (H5P_DEFAULT==fapl_id || H5FD_GASS!=H5P_get_driver(plist)) {
        GASS_INFO_NULL (_fa.info);
        /* _fa.info = GASS_INFO_NULL; */
        /* _fa.info = {0,0}; */ /*default*/
        fa = &_fa;
    } else {
        fa = H5P_get_driver_info(plist);
        assert(fa);
    }
    
    /* When I come down here, the possible flag values and the correct
       responses are given here :-

       1. H5F_ACC_CREAT | H5F_ACC_RDWR | H5F_ACC_EXCL : The file is 
          a new one. Go ahead and open it in O_RDWR. 

       2. H5F_ACC_CREAT | H5F_ACC_RDWR | H5F_ACC_TRUNC : Use
          O_RDWR | O_TRUNC with gass_open.

       3. H5F_ACC_RDWR | H5F_ACC_TRUNC : File already exists. Truncate it.
	  
       4. H5F_ACC_RDWR : Use O_RDWR with gass_open

       5. H5F_ACC_RDWR is not set : Use O_RDONLY with gass_open

       One reason why we cannot simply pass on the flags to gass_open
       is that gass_open does not support many of them (e.g., O_CREAT)
    */

    
    if ((flags & H5F_ACC_CREAT) && (flags & H5F_ACC_RDWR) && (flags & H5F_ACC_EXCL)) {
      if ((fd = globus_gass_open (filename, O_RDWR|O_TRUNC)) < 0)
        HRETURN_ERROR(H5E_IO, H5E_CANTOPENFILE, NULL, "open failed");
    }
    else if ((flags & H5F_ACC_CREAT) && (flags & H5F_ACC_RDWR) && (flags & H5F_ACC_TRUNC)) {
      if ((fd = globus_gass_open (filename, O_RDWR|O_TRUNC)) < 0)
        HRETURN_ERROR(H5E_IO, H5E_CANTOPENFILE, NULL, "open failed");
      
    }
    else if ((flags & H5F_ACC_RDWR) && (flags & H5F_ACC_TRUNC)) {
      if ((fd = globus_gass_open (filename, O_RDWR|O_TRUNC)) < 0)
        HRETURN_ERROR(H5E_IO, H5E_CANTOPENFILE, NULL, "open failed");
    
    }
    else if (flags & H5F_ACC_RDWR) {
      printf ("I'm here in H5FDgass_open going to call globus_gass_open with O_RDWR. \n");
      printf ("Name of URL =%s \n", filename);
      if ((fd = globus_gass_open (filename, O_RDWR)) < 0)
        HRETURN_ERROR(H5E_IO, H5E_CANTOPENFILE, NULL, "open failed");
      
    }
    else { /* This is case where H5F_ACC_RDWR is not set */
      if ((fd = globus_gass_open (filename, O_RDONLY)) < 0)
        HRETURN_ERROR(H5E_IO, H5E_CANTOPENFILE, NULL, "open failed");
      
    }
   
     if (HDfstat(fd, &sb)<0) {
        close(fd);
        HRETURN_ERROR(H5E_IO, H5E_BADFILE, NULL, "fstat failed");
    }

    /* Create the new file struct */
    if (NULL==(file=H5MM_calloc(sizeof(H5FD_gass_t))))
        HRETURN_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "can't allocate file struct");
    file->fd = fd;
    file->eof = sb.st_size;
    file->pos = HADDR_UNDEF;
    file->op = OP_UNKNOWN;
    file->info = fa->info;
    
    FUNC_LEAVE((H5FD_t*)file);
}

/*-------------------------------------------------------------------------
 * Function:	H5FD_gass_close
 *
 * Purpose:	Closes a GASS file.
 *
 * Return:	Success:	0
 *
 *		Failure:	-1, file not closed.
 *
 * Programmer:	Saurabh Bagchi
 *              Monday, August 16, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5FD_gass_close (H5FD_t *_file)
{
    H5FD_gass_t *file = (H5FD_gass_t *)_file;

    FUNC_ENTER(H5FD_gass_close, FAIL);

	if (file == NULL)
	  HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid file handle");
	
	if (globus_gass_close (file->fd) < 0)
	  HRETURN_ERROR(H5E_IO, H5E_CANTCLOSEFILE, FAIL, "can't close GASS file");

    H5MM_xfree(file);

    FUNC_LEAVE(SUCCEED);
}

	

/*-------------------------------------------------------------------------
 * Function:	H5FD_gass_query
 *
 * Purpose:	Set the flags that this VFL driver is capable of supporting.
 *              (listed in H5FDpublic.h)
 *
 * Return:	Success:	non-negative
 *
 *		Failure:	negative
 *
 * Programmer:	Quincey Koziol
 *              Tuesday, September 26, 2000
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5FD_gass_query(const UNUSED H5FD_t *_f, unsigned long *flags /* out */)
{
    herr_t ret_value=SUCCEED;

    FUNC_ENTER(H5FD_gass_query, FAIL);

    /* Set the VFL feature flags that this driver supports */
    if(flags) {
        *flags = 0;
        *flags|=H5FD_FEAT_DATA_SIEVE;       /* OK to perform data sieving for faster raw data reads & writes */
    }

    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5FD_gass_get_eoa
 *
 * Purpose:	Gets the end-of-address marker for the file. The EOA marker
 *              is the first address past the last byte allocated in the
 *              format address space.
 *
 * Return:	Success:	The end-of-address marker.
 *
 *		Failure:	HADDR_UNDEF
 *
 * Programmer:  Saurabh Bagchi
 *              Monday, August 16, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static haddr_t
H5FD_gass_get_eoa(H5FD_t *_file)
{
	H5FD_gass_t *file = (H5FD_gass_t *)_file;

    FUNC_ENTER(H5FD_gass_get_eoa, HADDR_UNDEF);

    FUNC_LEAVE(file->eoa);
}


/*-------------------------------------------------------------------------
 * Function:    H5FD_gass_set_eoa
 *
 * Purpose:     Set the end-of-address marker for the file. This function is
 *              called shortly after an existing HDF5 file is opened in order
 *              to tell the driver where the end of the HDF5 data is located.
 *
 * Return:      Success:        0
 *
 * Programmer:  Saurabh Bagchi
 *              Monday, August 16, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5FD_gass_set_eoa(H5FD_t *_file, haddr_t addr)
{
    H5FD_gass_t *file = (H5FD_gass_t *)_file;

    FUNC_ENTER(H5FD_gass_set_eoa, FAIL);

    file->eoa = addr;

    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:    H5FD_gass_get_eof
 *
 * Purpose:     Returns the end-of-file marker, which is the greater of
 *              either the Unix end-of-file or the HDF5 end-of-address
 *              markers.
 *
 * Return:      Success:        End of file address, the first address past
 *                              the end of the "file", either the Unix file
 *                              or the HDF5 file.
 *
 *              Failure:        HADDR_UNDEF
 *
 * Programmer:  Saurabh Bagchi
 *              Monday, August 16, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static haddr_t
H5FD_gass_get_eof(H5FD_t *_file)
{
    H5FD_gass_t *file = (H5FD_gass_t*)_file;

    FUNC_ENTER(H5FD_gass_get_eof, HADDR_UNDEF);

    FUNC_LEAVE(MAX(file->eof, file->eoa));
}

/*-------------------------------------------------------------------------
 * Function:    H5FD_gass_read
 *
 * Purpose:     Reads SIZE bytes of data from FILE beginning at address ADDR
 *              into buffer BUF.
 *
 * Return:      Success:        Zero. Result is stored in caller-supplied
 *                              buffer BUF.
 *
 *              Failure:        -1, Contents of buffer BUF are undefined.
 *
 * Programmer:  Saurabh Bagchi
 *              Monday, August 16, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5FD_gass_read(H5FD_t *_file, H5FD_mem_t UNUSED type, hid_t dxpl_id/*unused*/, haddr_t addr,
               size_t size, void *buf/*out*/)
{
    H5FD_gass_t         *file = (H5FD_gass_t*)_file;
    ssize_t             nbytes;

    FUNC_ENTER(H5FD_gass_read, FAIL);

    assert(file && file->pub.cls);
    assert(buf);

    /* Check for overflow conditions */
    if (HADDR_UNDEF==addr)
        HRETURN_ERROR(H5E_ARGS, H5E_BADRANGE, FAIL, "addr undefined");
    if (REGION_OVERFLOW(addr, size))
        HRETURN_ERROR(H5E_ARGS, H5E_OVERFLOW, FAIL, "addr too large");
    if (addr+size>file->eoa)
        HRETURN_ERROR(H5E_ARGS, H5E_OVERFLOW, FAIL, "addr too large");

    /* Seek to the correct location */
    if ((addr!=file->pos || OP_READ!=file->op) &&
            file_seek(file->fd, (file_offset_t)addr, SEEK_SET)<0) {
        file->pos = HADDR_UNDEF;
        file->op = OP_UNKNOWN;
        HRETURN_ERROR(H5E_IO, H5E_SEEKERROR, FAIL, "gass file seek failed");
    }

    /*
     * Read data, being careful of interrupted system calls, partial results,
     * and the end of the file.
     */
    while (size>0) {
        do 
            nbytes = read(file->fd, buf, size);
        while (-1==nbytes && EINTR==errno);

        if (-1==nbytes) {
            /* error */
            file->pos = HADDR_UNDEF;
            file->op = OP_UNKNOWN;
            HRETURN_ERROR(H5E_IO, H5E_READERROR, FAIL, "gass file read failed");
        }
        if (0==nbytes) {
            /* end of file but not end of format address space */
            memset(buf, 0, size);
            size = 0;
        }
        assert(nbytes>=0);
        assert(nbytes<=size);
        size -= (hsize_t)nbytes;
        addr += (haddr_t)nbytes;
        buf = (char*)buf + nbytes;
    }

    /* Update current position */
    file->pos = addr;
    file->op = OP_READ;
    FUNC_LEAVE(SUCCEED);
}

/*-------------------------------------------------------------------------
 * Function:    H5FD_gass_write
 *
 * Purpose:     Writes SIZE bytes of data to FILE beginning at address ADDR
 *              from buffer BUF.
 *
 * Return:      Success:        Zero
 *
 *              Failure:        -1
 *
 * Programmer:  Saurabh Bagchi
 *              Tuesday, August 17, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5FD_gass_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id/*unused*/, haddr_t addr,
                size_t size, const void *buf)
{
    H5FD_gass_t         *file = (H5FD_gass_t*)_file;
    ssize_t             nbytes;

    FUNC_ENTER(H5FD_gass_write, FAIL);

    assert(file && file->pub.cls);
    assert(buf);

    /* Check for overflow conditions */
    if (HADDR_UNDEF==addr)
        HRETURN_ERROR(H5E_ARGS, H5E_BADRANGE, FAIL, "addr undefined");
    if (REGION_OVERFLOW(addr, size))
        HRETURN_ERROR(H5E_ARGS, H5E_OVERFLOW, FAIL, "addr too large");
    if (addr+size>file->eoa)
        HRETURN_ERROR(H5E_ARGS, H5E_OVERFLOW, FAIL, "addr too large");

    /* Seek to the correct location */
    if ((addr!=file->pos || OP_WRITE!=file->op) &&
        file_seek(file->fd, (file_offset_t)addr, SEEK_SET)<0) {
        file->pos = HADDR_UNDEF;
        file->op = OP_UNKNOWN;
        HRETURN_ERROR(H5E_IO, H5E_SEEKERROR, FAIL, "gass file seek failed");
    }

    /*
     * Write the data, being careful of interrupted system calls and partial
     * results
     */
    while (size>0) {
        do
            nbytes = write(file->fd, buf, size);
        while (-1==nbytes && EINTR==errno);

        if (-1==nbytes) {
            /* error */
            file->pos = HADDR_UNDEF;
            file->op = OP_UNKNOWN;
            HRETURN_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "gass file write failed");
        }
        assert(nbytes>0);
        assert(nbytes<=size);
        size -= (hsize_t)nbytes;
        addr += (haddr_t)nbytes;
        buf = (const char*)buf + nbytes;
    }

    /* Update current position and eof */
    file->pos = addr;
    file->op = OP_WRITE;
    if (file->pos>file->eof)
        file->eof = file->pos;

    FUNC_LEAVE(SUCCEED);
}

#endif  /* H5_HAVE_GASS */