Should not assume file exist at a open call

[wangvsa]

This is a small assumption issue.
unifyfs_fid_open function assumes the file must exist after an open call. But the file may be opened without "O_CREAT" flag; For example, some applications use the open call to test for file existence. In this case, we should not print out an error (line 564).
Fix: replace LOGERR to LOGDBG. I will create a PR to fix this.

UnifyFS/client/src/unifyfs_fid.c

Lines 517 to 566 in e07093f

	int unifyfs_fid_open(
	unifyfs_client* client,
	const char* path, /* path of file to be opened */
	int flags, /* flags bits as from open(2) */
	mode_t mode, /* mode bits as from open(2) */
	int* outfid, /* allocated local file id if open is successful */
	off_t* outpos) /* initial file position if open is successful */
	{
	int ret = UNIFYFS_SUCCESS;
	/* check that pathname is within bounds */
	size_t pathlen = strlen(path) + 1;
	if (pathlen > UNIFYFS_MAX_FILENAME) {
	return ENAMETOOLONG;
	}
	int gfid = unifyfs_generate_gfid(path);
	/* attempt to create file if requested */
	if (flags & O_CREAT) {
	/* Ensure that we're only creating a regular file. */
	int type = mode & S_IFMT;
	if (type & ~S_IFREG) {
	LOGERR("Only regular files can be created %s S_IFMT bits %x",
	path, type);
	return EINVAL;
	}
	mode |= S_IFREG;
	int exclusive = (flags & O_EXCL);
	int private = (exclusive && client->use_excl_private);
	int truncate = (flags & O_TRUNC);
	ret = unifyfs_gfid_create(client, path,
	exclusive, private, truncate, mode);
	if (ret != UNIFYFS_SUCCESS) {
	return ret;
	}
	}
	/* File should exist at this point,
	* update our cache with its metadata. */
	ret = unifyfs_fid_fetch(client, path);
	if (ret != UNIFYFS_SUCCESS) {
	/* Failed to get metadata for a file that should exist.
	* Perhaps it was since deleted. We could try to create
	* it again and loop through these steps, but for now
	* consider this situation to be an error. */
	LOGERR("Failed to get metadata on existing file %s", path);
	return ret;
	}

[MichaelBrim]

@wangvsa Yes, I agree it shouldn't be treated as an error for logging purposes - LOGDBG is good. We should also change the message to remove the word "existing"