Hi all, After the set of issues discussed here, it seems to me that it would be a good thing to have some safeguards against incorrect flags when opening a fd which would be used for fsync(): https://www.postgresql.org/message-id/16039-196fc97cc05e1...@postgresql.org
Attached is a patch aimed at doing that. Historically O_RDONLY is 0, so when looking at a directory we just need to make sure that no write flags are used. For files, that's the contrary, a write flag has to be used. Thoughts or better ideas? Thanks, -- Michael
diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 94be62fa6e..791afcae4a 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -330,6 +330,28 @@ static int fsync_parent_path(const char *fname, int elevel);
int
pg_fsync(int fd)
{
+#ifdef USE_ASSERT_CHECKING
+ struct stat st;
+
+ /*
+ * On some operating systems fsyncing a file requires O_RDWR, and
+ * a directory requires O_RDONLY. Ignore any errors.
+ */
+ if (fstat(fd, &st) == 0)
+ {
+ int desc_flags = fcntl(fd, F_GETFL);
+
+ /*
+ * O_RDONLY is historically 0, so just make sure that for
+ * directories no write flags are used.
+ */
+ if (!S_ISDIR(st.st_mode))
+ Assert((desc_flags & (O_RDWR | O_WRONLY)) != 0);
+ else
+ Assert((desc_flags & (O_RDWR | O_WRONLY)) == 0);
+ }
+#endif
+
/* #if is to skip the sync_method test if there's no need for it */
#if defined(HAVE_FSYNC_WRITETHROUGH) && !defined(FSYNC_WRITETHROUGH_IS_FSYNC)
if (sync_method == SYNC_METHOD_FSYNC_WRITETHROUGH)
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