Re: [PATCH v2] uapi/fcntl: define RENAME_* and AT_RENAME_* macros
From: Amir Goldstein <amir73il@gmail.com>
Date: 2025-09-02 06:58:53
Also in:
linux-fsdevel, linux-patches
Subsystem:
file locking (flock() and fcntl()/lockf()), the rest · Maintainers:
Jeff Layton, Chuck Lever, Linus Torvalds
On Tue, Sep 2, 2025 at 1:14 AM Randy Dunlap [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Define the RENAME_* and AT_RENAME_* macros exactly the same as in recent glibc <stdio.h> so that duplicate definition build errors in both samples/watch_queue/watch_test.c and samples/vfs/test-statx.c no longer happen. When they defined in exactly the same way in multiple places, the build errors are prevented. Defining only the AT_RENAME_* macros is not sufficient since they depend on the RENAME_* macros, which may not be defined when the AT_RENAME_* macros are used. Build errors being fixed: 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 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 | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)--- linux-next-20250819.orig/include/uapi/linux/fcntl.h +++ linux-next-20250819/include/uapi/linux/fcntl.h@@ -156,9 +156,12 @@ */ /* Flags for renameat2(2) (must match legacy RENAME_* flags). */ -#define AT_RENAME_NOREPLACE 0x0001 -#define AT_RENAME_EXCHANGE 0x0002 -#define AT_RENAME_WHITEOUT 0x0004 +# define RENAME_NOREPLACE (1 << 0) +# define AT_RENAME_NOREPLACE RENAME_NOREPLACE +# define RENAME_EXCHANGE (1 << 1) +# define AT_RENAME_EXCHANGE RENAME_EXCHANGE +# define RENAME_WHITEOUT (1 << 2) +# define AT_RENAME_WHITEOUT RENAME_WHITEOUT
This solution, apart from being terribly wrong (adjust the source to match to value of its downstream copy), does not address the issue that Mathew pointed out on v1 discussion [1]: $ grep -r AT_RENAME_NOREPLACE /usr/include /usr/include/linux/fcntl.h:#define AT_RENAME_NOREPLACE 0x0001 It's not in stdio.h at all. This is with libc6 2.41-10 [1] https://lore.kernel.org/linux-fsdevel/aKxfGix_o4glz8-Z@casper.infradead.org/ (local) I don't know how to resolve the mess that glibc has created. Perhaps like this:
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index f291ab4f94ebc..dde14fa3c2007 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h@@ -155,10 +155,16 @@ * as possible, so we can use them for generic bits in the future if necessary. */ -/* Flags for renameat2(2) (must match legacy RENAME_* flags). */ -#define AT_RENAME_NOREPLACE 0x0001 -#define AT_RENAME_EXCHANGE 0x0002 -#define AT_RENAME_WHITEOUT 0x0004 +/* + * The legacy renameat2(2) RENAME_* flags are conceptually also
syscall-specific + * flags, so it could makes sense to create the AT_RENAME_* aliases for them and + * maybe later add support for generic AT_* flags to this syscall. + * However, following a mismatch of definitions in glibc and since no kernel code + * currently uses the AT_RENAME_* aliases, we leave them undefined here. +#define AT_RENAME_NOREPLACE RENAME_NOREPLACE +#define AT_RENAME_EXCHANGE RENAME_EXCHANGE +#define AT_RENAME_WHITEOUT RENAME_WHITEOUT +*/ /* Flag for faccessat(2). */ #define AT_EACCESS 0x200 /* Test access permitted for