Commit cf47d283d101e5d8e0d1ca7ec427d40efc40f358 | zig

author	Pat Tullmann <pat.github@tullmann.org> 2025-07-19 09:34:04-07:00
committer	Pat Tullmann <pat.github@tullmann.org> 2025-08-06 22:12:42-07:00
log	cf47d283d101e5d8e0d1ca7ec427d40efc40f358
tree	96494f4cd5859c4ba30d375552912c4445f9a2ab
parent	caf80e90b85a2a7855c369887dce163cf036ff7e

lib/std/posix/test.zig: don't compare blksize in "fstatat"

In trying to reproduce the race in #24380, my system tripped over the stat
"blocks" field changing in this test.  The value was almost always 8
(effectively 4k) or very infrequently 0 (I saw the 0 from both `fstat` and
`fstatat`).  I believe the underlying filesystem is free to asynchronously
change this value. For example, if it migrates a file between some
"inline" or maybe journal storage, and actual on-disk blocks.  So it seems
plausible that its allowed to change between stat calls.

Breaking up the struct comparison this way means we also don't compare any
of the padding or "reserved" fields, too.  And we can narrow down the
s390x-linux work-around.

1 files changed, 21 insertions(+), 5 deletions(-)

lib
- std
  - posix
    test.zig

lib/std/posix/test.zig+21-5

...	@@ -395,11 +395,27 @@ test "fstatat" {	...	@@ -395,11 +395,27 @@ test "fstatat" {
395	// now repeat but using `fstatat` instead	395	// now repeat but using `fstatat` instead
396	const statat = try posix.fstatat(tmp.dir.fd, "file.txt", posix.AT.SYMLINK_NOFOLLOW);	396	const statat = try posix.fstatat(tmp.dir.fd, "file.txt", posix.AT.SYMLINK_NOFOLLOW);
397		397
398	// s390x-linux does not have nanosecond precision for fstat(), but it does for fstatat(). As a	398	try expectEqual(stat.dev, statat.dev);
399	// result, comparing the two structures is doomed to fail.	399	try expectEqual(stat.ino, statat.ino);
400	if (builtin.cpu.arch == .s390x and builtin.os.tag == .linux) return error.SkipZigTest;	400	try expectEqual(stat.nlink, statat.nlink);
401		401	try expectEqual(stat.mode, statat.mode);
402	try expectEqual(stat, statat);	402	try expectEqual(stat.uid, statat.uid);
		403	try expectEqual(stat.gid, statat.gid);
		404	try expectEqual(stat.rdev, statat.rdev);
		405	try expectEqual(stat.size, statat.size);
		406	try expectEqual(stat.blksize, statat.blksize);
		407
		408	// The stat.blocks/statat.blocks count is managed by the filesystem and may
		409	// change if the file is stored in a journal or "inline".
		410	// try expectEqual(stat.blocks, statat.blocks);
		411
		412	// s390x-linux does not have nanosecond precision for fstat(), but it does for
		413	// fstatat(). As a result, comparing the timestamps isn't worth the effort
		414	if (!(builtin.cpu.arch == .s390x and builtin.os.tag == .linux)) {
		415	try expectEqual(stat.atime(), statat.atime());
		416	try expectEqual(stat.mtime(), statat.mtime());
		417	try expectEqual(stat.ctime(), statat.ctime());
		418	}
403	}	419	}
404		420
405	test "readlinkat" {	421	test "readlinkat" {