Hi,
please find attached the diff for the readv and writev man pages to cover the
preadv and pwritev system calls.
Ciao
Stephan
--- readv.2 2011-02-09 14:12:18.609148000 +0100
+++ readv.2.new 2011-02-09 14:13:45.669148002 +0100
@@ -28,7 +28,7 @@
.\"
.TH READV 2 2002-10-17 "Linux" "Linux Programmer's Manual"
.SH NAME
-readv, writev \- read or write data into multiple buffers
+readv, writev, preadv, pwritev \- read or write data into multiple buffers
.SH SYNOPSIS
.nf
.B #include <sys/uio.h>
@@ -36,6 +36,12 @@
.BI "ssize_t readv(int " fd ", const struct iovec *" iov ", int " iovcnt );
.sp
.BI "ssize_t writev(int " fd ", const struct iovec *" iov ", int " iovcnt );
+.sp
+.BI "ssize_t preadv(int " fd ", const struct iovec *" iov ", int " iovcnt ,
+.BI " unsigned long " pos_l ", unsigned long " pos_h );
+.sp
+.BI "ssize_t pwritev(int " fd ", const struct iovec *" iov ", int " iovcnt ,
+.BI " unsigned long " pos_l ", unsigned long " pos_h );
.fi
.SH DESCRIPTION
The
@@ -58,6 +64,32 @@
.I fd
("gather output").
.PP
+The
+.BR preadv ()
+function reads
+.I iovcnt
+buffers from the file associated with the file descriptor
+.I fd
+into the buffers described by
+.I iov
+("scatter input") at an offset defined with
+.I pos_l
+and
+.IR pos_h .
+.PP
+The
+.BR pwritev ()
+function writes
+.I iovcnt
+buffers of data described by
+.I iov
+to the file associated with the file descriptor
+.I fd
+("scatter input") at an offset defined with
+.I pos_l
+and
+.IR pos_h .
+.PP
The pointer
.I iov
points to an array of
@@ -77,22 +109,42 @@
.fi
.in
.PP
+The file offset specified for
+.BR preadv ()
+and
+.BR pwritev ()
+is defined by the parameters of
+.I pos_l
+and
+.IR pos_h .
+The kernel concatinates the low 16 bit of
+.I pos_h
+with all bits of
+.I pos_l
+to derive the file offset where the read or write operations start.
+.PP
The
.BR readv ()
-function works just like
+and
+.BR preadv ()
+functions work just like
.BR read (2)
except that multiple buffers are filled.
.PP
The
.BR writev ()
-function works just like
+and
+.BR pwritev ()
+functions work just like
.BR write (2)
except that multiple buffers are written out.
.PP
Buffers are processed in array order.
This means that
.BR readv ()
-completely fills
+and
+.BR preadv ()
+completely fill
.IR iov [0]
before proceeding to
.IR iov [1],
@@ -102,25 +154,33 @@
may be filled.)
Similarly,
.BR writev ()
-writes out the entire contents of
+and
+.BR pwritev ()
+write out the entire contents of
.IR iov [0]
before proceeding to
.IR iov [1],
and so on.
.PP
The data transfers performed by
-.BR readv ()
+.BR readv (),
+.BR preadv (),
+.BR writev (),
and
-.BR writev ()
+.BR pwritev ()
are atomic: the data written by
.BR writev ()
+and
+.BR pwritev ()
is written as a single block that is not intermingled with output
from writes in other processes (but see
.BR pipe (7)
for an exception);
analogously,
.BR readv ()
-is guaranteed to read a contiguous block of data from the file,
+and
+.BR preadv ()
+are guaranteed to read a contiguous block of data from the file,
regardless of read operations performed in other threads or processes
that have file descriptors referring to the same open file description
(see
@@ -128,9 +188,13 @@
.SH "RETURN VALUE"
On success, the
.BR readv ()
-function returns the number of bytes read; the
+and
+.BR preadv ()
+functions return the number of bytes read; the
.BR writev ()
-function returns the number of bytes written.
+and
+.BR pwritev ()
+functions return the number of bytes written.
On error, \-1 is returned, and \fIerrno\fP is set appropriately.
.SH ERRORS
The errors are as given for
