[PATCH] posix: Add p{read,write}v2 RWF_NOWAIT flag (BZ#21738)

[Adhemerval Zanella]

On 10/07/2017 16:36, Zack Weinberg wrote:
> Argh, one more thing:
> 
> On Mon, Jul 10, 2017 at 3:34 PM, Zack Weinberg <zackw@panix.com> wrote:
>>
>> Suggest instead "Use nonblocking mode for this operation; that is,
>> this call to @code{preadv2} will fail and set @code{errno} to
>> @code{EAGAIN} if the operation would block."
> 
> "... this call to @code{preadv2} or @code{pwritev2} ..." It does work
> in both, right?
> 
> zw
> 

That's the new version:

	[BZ #21738]
	* manual/llio.texi (RWF_NOWAIT): New item.
	* misc/tst-preadvwritev2-common.c (do_test_with_invalid_flags):
	Add RWF_NOWAIT check.
	* sysdeps/unix/sysv/linux/bits/uio-ext.h (RWF_NOWAIT): New flag.

---

diff --git a/manual/llio.texi b/manual/llio.texi
index ba1f455..e72c53c 100644
--- a/manual/llio.texi
+++ b/manual/llio.texi
@@ -770,6 +770,10 @@ Per-IO synchronization as if the file was opened with @code{O_DSYNC} flag.
 
 @item RWF_SYNC
 Per-IO synchronization as if the file was opened with @code{O_SYNC} flag.
+
+@item RWF_NOWAIT
+Use nonblocking mode for this operation; that is, this call to @code{preadv2}
+will fail and set @code{errno} to @code{EAGAIN} if the operation would block.
 @end vtable
 
 When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
diff --git a/misc/tst-preadvwritev2-common.c b/misc/tst-preadvwritev2-common.c
index 4c53d56..8abedc1 100644
--- a/misc/tst-preadvwritev2-common.c
+++ b/misc/tst-preadvwritev2-common.c
@@ -16,21 +16,16 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#include <limits.h>
 #include <support/check.h>
 
 static void
 do_test_with_invalid_flags (void)
 {
-  int invalid_flag = 0x1;
-#ifdef RWF_HIPRI
-  invalid_flag <<= 1;
-#endif
-#ifdef RWF_DSYNC
-  invalid_flag <<= 1;
-#endif
-#ifdef RWF_SYNC
-  invalid_flag <<= 1;
-#endif
+#define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT)
+  /* Set the next bit from the mask of all supported flags.  */
+  int invalid_flag = __builtin_clz (RWF_SUPPORTED);
+  invalid_flag = 0x1 << ((sizeof (int) * CHAR_BIT) - invalid_flag);
 
   char buf[32];
   const struct iovec vec = { .iov_base = buf, .iov_len = sizeof (buf) };
diff --git a/sysdeps/unix/sysv/linux/bits/uio-ext.h b/sysdeps/unix/sysv/linux/bits/uio-ext.h
index 4ddb644..12cd78e 100644
--- a/sysdeps/unix/sysv/linux/bits/uio-ext.h
+++ b/sysdeps/unix/sysv/linux/bits/uio-ext.h
@@ -46,6 +46,10 @@ extern ssize_t process_vm_writev (pid_t __pid, const struct iovec *__lvec,
 #define RWF_HIPRI	0x00000001 /* High priority request.  */
 #define RWF_DSYNC	0x00000002 /* per-IO O_DSYNC.  */
 #define RWF_SYNC	0x00000004 /* per-IO O_SYNC.  */
+#define RWF_NOWAIT	0x00000008 /* per-IO, return -EAGAIN if operation
+				      would block */
+#define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT)
+
 
 __END_DECLS
 
-- 
2.7.4