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readv.2: Tweaks to Christoph's patch 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-04-18 14:53:11 +01:00
parent d948a87054
commit 3b31ec64ab
1 changed files with 31 additions and 24 deletions
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55
man2/readv.2
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@ -186,38 +186,41 @@ The file referred to by
must be capable of seeking.
.SS preadv2() and pwritev2()
This pair of system calls has similar functionality to the
These system calls are similar to
.BR preadv ()
and
.BR pwritev ()
calls, but adds a fifth argument, \fIflags\fP, which modifies the behavior on a per call basis.
calls, but add a fifth argument,
.IR flags ,
which modifies the behavior on a per-call basis.
Like the
Unlike
.BR preadv ()
and
.BR pwritev ()
calls, they accept an \fIoffset\fP argument. Unlike those calls, if the \fIoffset\fP argument is set to -1 then the current file offset is used and updated.
.BR pwritev (),
if the
.I offset
argument is \-1, then the current file offset is used and updated.
The \fIflags\fP arguments to
.BR preadv2 ()
and
.BR pwritev2 ()
contains a bitwise OR of one or more of the following flags:
The
.I flags
argument contains a bitwise OR of zero or more of the following flags:
.TP
.BR RWF_HIPRI " (since Linux 4.6)"
High priority read/write. Allows block based filesystems to use polling of the
device, which provides lower latency, but may use additional ressources. (Currently
only usable on a file descriptor opened using the
.BR O_DIRECT " flag)."
High priority read/write.
Allows block-based filesystems to use polling of the device,
which provides lower latency, but may use additional resources.
(Currently, this feature is usable only on a file descriptor opened using the
.BR O_DIRECT
flag.)
.SH RETURN VALUE
On success,
.BR readv () ","
.BR readv (),
.BR preadv ()
and
.BR preadv2 ()
return the number of bytes read;
.BR writev () ","
.BR writev (),
.BR pwritev ()
and
.BR pwritev2 ()
@ -236,9 +239,9 @@ The errors are as given for
and
.BR write (2).
Furthermore,
.BR preadv () ","
.BR preadv2 () ","
.BR pwritev ()
.BR preadv (),
.BR preadv2 (),
.BR pwritev (),
and
.BR pwritev2 ()
can also fail for the same reasons as
@ -253,14 +256,18 @@ values overflows an
value.
.TP
.B EINVAL
The vector count \fIiovcnt\fP is less than zero or greater than the
permitted maximum. Or, an unknown flag is specified in \fIflags\fP.
The vector count,
.IR iovcnt ,
is less than zero or greater than the permitted maximum.
.TP
.B EINVAL
An unknown flag is specified in \fIflags\fP.
.SH VERSIONS
.BR preadv ()
and
.BR pwritev ()
first appeared in Linux 2.6.30; library support was added in glibc 2.10.
.sp
.BR preadv2 ()
and
.BR pwritev2 ()
@ -281,7 +288,7 @@ nonstandard, but present also on the modern BSDs.
.sp
.BR preadv2 (),
.BR pwritev2 ():
nonstandard, Linux extension.
nonstandard Linux extension.
.SH NOTES
POSIX.1 allows an implementation to place a limit on
the number of items that can be passed in