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authorQuincey Koziol <koziol@hdfgroup.org>2018-04-01 18:04:37 (GMT)
committerQuincey Koziol <koziol@hdfgroup.org>2018-04-01 18:04:37 (GMT)
commitbe51656400c4b809f144844629e1cef7d2d7356c (patch)
tree121912d12f23a63af2345b688f765f8a0ef400dd
parentd834e9158c8dd55c30a7fe13a142cfa124c02513 (diff)
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Add comment for the file flush when the file low / high bounds are changed
after a file is open.
-rw-r--r--src/H5Fint.c19
1 files changed, 19 insertions, 0 deletions
diff --git a/src/H5Fint.c b/src/H5Fint.c
index c5d281d..49538f4 100644
--- a/src/H5Fint.c
+++ b/src/H5Fint.c
@@ -2788,6 +2788,25 @@ H5F__set_libver_bounds(H5F_t *f, H5F_libver_t low, H5F_libver_t high)
/* Set the bounds only if the existing setting is different from the inputs */
if(f->shared->low_bound != low || f->shared->high_bound != high) {
/* Call the flush routine, for this file */
+ /* Note: This is done in case the binary format for representing a
+ * metadata entry class changes when the file format low / high
+ * bounds are changed and an unwritten entry of that class is
+ * sitting in the metadata cache.
+ *
+ * If that happens, it's possible that the entry's size could
+ * become larger, potentially corrupting the file (if the larger
+ * entry is fully written, overwriting data outside its allocated
+ * space), or corrupting the entry (if the entry is truncated to
+ * fit into the allocated space).
+ *
+ * Although I'm not aware of any metadata with this behavior
+ * currently, it would be very difficult to guard against and / or
+ * detect, but if we flush everything here, the format version
+ * for metadata entries in the cache will be finalized and these
+ * sorts of problems can be avoided.
+ *
+ * QAK - April, 2018
+ */
if(H5F__flush_real(f) < 0)
HGOTO_ERROR(H5E_FILE, H5E_CANTFLUSH, FAIL, "unable to flush file's cached information")