On 2025-09-04, Amir Goldstein [off-list ref] wrote:

On Thu, Sep 4, 2025 at 8:22 AM Randy Dunlap [off-list ref] wrote:

quoted

Don't define the AT_RENAME_* macros at all since the kernel does not
use them nor does the kernel need to provide them for userspace.
Leave them as comments in <uapi/linux/fcntl.h> only as an example.

The AT_RENAME_* macros have recently been added to glibc's <stdio.h>.
For a kernel allmodconfig build, this made the macros be defined
differently in 2 places (same values but different macro text),
causing build errors/warnings (duplicate definitions) in both
samples/watch_queue/watch_test.c and samples/vfs/test-statx.c.
(<linux/fcntl.h> is included indirecty in both programs above.)

Fixes: b4fef22c2fb9 ("uapi: explain how per-syscall AT_* flags should be allocated")
Signed-off-by: Randy Dunlap <redacted>
---
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Chuck Lever <redacted>
Cc: Alexander Aring <alex.aring@gmail.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Aleksa Sarai <redacted>
Cc: Jan Kara <jack@suse.cz>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Howells <dhowells@redhat.com>
CC: linux-api@vger.kernel.org
To: linux-fsdevel@vger.kernel.org
---
 include/uapi/linux/fcntl.h |    6 ++++++
 1 file changed, 6 insertions(+)

--- linux-next-20250819.orig/include/uapi/linux/fcntl.h
+++ linux-next-20250819/include/uapi/linux/fcntl.h

@@ -155,10 +155,16 @@
  * as possible, so we can use them for generic bits in the future if necessary.
  */

+/*
+ * Note: This is an example of how the AT_RENAME_* flags could be defined,
+ * but the kernel has no need to define them, so leave them as comments.
+ */
 /* Flags for renameat2(2) (must match legacy RENAME_* flags). */
+/*
 #define AT_RENAME_NOREPLACE    0x0001
 #define AT_RENAME_EXCHANGE     0x0002
 #define AT_RENAME_WHITEOUT     0x0004
+*/

I find this end result a bit odd, but I don't want to suggest another variant
I already proposed one in v2 review [1] that maybe you did not like.
It's fine.
I'll let Aleksa and Christian chime in to decide on if and how they want this
comment to look or if we should just delete these definitions and be done with
this episode.

For my part, I'm fine with these becoming comments or even removing them
outright. I think that defining them as AT_* flags would've been useful
examples of how these flags should be used, but it is what it is.

Then again, AT_EXECVE_CHECK went in and used a higher-level bit despite
the comments describing that this was unfavourable and what should be
done instead, so maybe attempting to avoid conflicts is an exercise in
futility...

If it's too much effort to synchronise them between glibc then it's
better to just close the book on this whole chapter (even though my
impression is that glibc made a mistake or two when adding the
definitions).

In either case, feel free to take my

Acked-by: Aleksa Sarai <redacted>

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/