misc: Add support for Linux uio.h RWF_ATOMIC flag

Linux 6.11 adds the new flag for pwritev2 (commit
c34fc6f26ab86d03a2d47446f42b6cd492dfdc56).

Checked on x86_64-linux-gnu on 6.11 kernel.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

manual/llio.texi

@@ -1381,6 +1381,19 @@ Per-IO synchronization as if the file was opened with @code{O_APPEND} flag.
 @item RWF_NOAPPEND
 This flag allows an offset to be honored, even if the file was opened with
 @code{O_APPEND} flag.
+
+@item RWF_ATOMIC
+Indicate that the write is to be issued with torn-write prevention.  The
+input buffer should follow some contraints: the total length should be
+power-of-2 in size and also sizes between @code{atomic_write_unit_min}
+and @code{atomic_write_unit_max}, the @code{struct iovec} count should be
+up to @code{atomic_write_segments_max}, and the offset should be
+naturally-aligned with regard to total write length.
+
+The @code{atomic_*} values can be obtained with @code{statx} along with
+@code{STATX_WRITE_ATOMIC} flag.
+
+This is a Linux-specific extension.
 @end vtable
 
 When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the

misc/tst-preadvwritev2-common.c

@@ -37,8 +37,11 @@
 #ifndef RWF_NOAPPEND
 # define RWF_NOAPPEND 0
 #endif
+#ifndef RWF_ATOMIC
+# define RWF_ATOMIC 0
+#endif
 #define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT \
-			 | RWF_APPEND | RWF_NOAPPEND)
+			 | RWF_APPEND | RWF_NOAPPEND | RWF_ATOMIC)
 
 /* Generic uio_lim.h does not define IOV_MAX.  */
 #ifndef IOV_MAX

sysdeps/unix/sysv/linux/bits/uio-ext.h

@@ -48,6 +48,8 @@ extern ssize_t process_vm_writev (pid_t __pid, const struct iovec *__lvec,
 #define RWF_NOWAIT	0x00000008 /* per-IO nonblocking mode.  */
 #define RWF_APPEND	0x00000010 /* per-IO O_APPEND.  */
 #define RWF_NOAPPEND	0x00000020 /* per-IO negation of O_APPEND */
+#define RWF_ATOMIC	0x00000040 /* Write is to be issued with torn-write
+				      prevention.  */
 
 __END_DECLS