Re: [PATCH] uapi/fcntl: conditionally define AT_RENAME* macros

On 8/24/25 4:21 PM, Matthew Wilcox wrote:

On Sun, Aug 24, 2025 at 03:10:55PM -0700, Randy Dunlap wrote:

quoted

Don't define the AT_RENAME_* macros when __USE_GNU is defined since
/usr/include/stdio.h defines them in that case (i.e. when _GNU_SOURCE
is defined, which causes __USE_GNU to be defined).

Having them defined in 2 places causes build warnings (duplicate
definitions) in both samples/watch_queue/watch_test.c and
samples/vfs/test-statx.c.

It does?  What flags?

for samples/vfs/test-statx.c:

In file included from ../samples/vfs/test-statx.c:23:
usr/include/linux/fcntl.h:159:9: warning: ‘AT_RENAME_NOREPLACE’ redefined
  159 | #define AT_RENAME_NOREPLACE     0x0001
In file included from ../samples/vfs/test-statx.c:13:
/usr/include/stdio.h:171:10: note: this is the location of the previous definition
  171 | # define AT_RENAME_NOREPLACE RENAME_NOREPLACE
usr/include/linux/fcntl.h:160:9: warning: ‘AT_RENAME_EXCHANGE’ redefined
  160 | #define AT_RENAME_EXCHANGE      0x0002
/usr/include/stdio.h:173:10: note: this is the location of the previous definition
  173 | # define AT_RENAME_EXCHANGE RENAME_EXCHANGE
usr/include/linux/fcntl.h:161:9: warning: ‘AT_RENAME_WHITEOUT’ redefined
  161 | #define AT_RENAME_WHITEOUT      0x0004
/usr/include/stdio.h:175:10: note: this is the location of the previous definition
  175 | # define AT_RENAME_WHITEOUT RENAME_WHITEOUT

for samples/watch_queue/watch_test.c:

In file included from usr/include/linux/watch_queue.h:6,
                 from ../samples/watch_queue/watch_test.c:19:
usr/include/linux/fcntl.h:159:9: warning: ‘AT_RENAME_NOREPLACE’ redefined
  159 | #define AT_RENAME_NOREPLACE     0x0001
In file included from ../samples/watch_queue/watch_test.c:11:
/usr/include/stdio.h:171:10: note: this is the location of the previous definition
  171 | # define AT_RENAME_NOREPLACE RENAME_NOREPLACE
usr/include/linux/fcntl.h:160:9: warning: ‘AT_RENAME_EXCHANGE’ redefined
  160 | #define AT_RENAME_EXCHANGE      0x0002
/usr/include/stdio.h:173:10: note: this is the location of the previous definition
  173 | # define AT_RENAME_EXCHANGE RENAME_EXCHANGE
usr/include/linux/fcntl.h:161:9: warning: ‘AT_RENAME_WHITEOUT’ redefined
  161 | #define AT_RENAME_WHITEOUT      0x0004
/usr/include/stdio.h:175:10: note: this is the location of the previous definition
  175 | # define AT_RENAME_WHITEOUT RENAME_WHITEOUT

#define AT_RENAME_NOREPLACE     0x0001
#define AT_RENAME_NOREPLACE     0x0001

int main(void)
{
	return AT_RENAME_NOREPLACE;
}

gcc -W -Wall testA.c -o testA

(no warnings)

I'm pretty sure C says that duplicate definitions are fine as long
as they're identical.

The vales are identical but the strings are not identical.

We can't fix stdio.h, but we could just change uapi/linux/fcntl.h
to match stdio.h. I suppose.

-- 
~Randy