Section (2) vmsplice
Name
vmsplice — splice user pages to/from a pipe
Synopsis
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> #include <sys/uio.h>
ssize_t
vmsplice( |
int fd, |
const struct iovec *iov, | |
unsigned long nr_segs, | |
unsigned int flags) ; |
DESCRIPTION
If fd
is opened
for writing, the vmsplice
()
system call maps nr_segs
ranges of user memory
described by iov
into
a pipe. If fd
is
opened for reading, the vmsplice
() system call fills nr_segs
ranges of user memory
described by iov
from
a pipe. The file descriptor fd
must refer to a pipe.
The pointer iov
points to an array of iovec
structures as defined in <
sys/uio.h
>
struct iovec { void * iov_base
; /* Starting address */size_t iov_len
; /* Number of bytes */};
The flags
argument
is a bit mask that is composed by ORing together zero or more
of the following values:
SPLICE_F_MOVE
-
Unused for
vmsplice
(); see splice(2). SPLICE_F_NONBLOCK
-
Do not block on I/O; see splice(2) for further details.
SPLICE_F_MORE
-
Currently has no effect for
vmsplice
(), but may be implemented in the future; see splice(2). SPLICE_F_GIFT
-
The user pages are a gift to the kernel. The application may not modify this memory ever, otherwise the page cache and on-disk data may differ. Gifting pages to the kernel means that a subsequent splice(2)
SPLICE_F_MOVE
can successfully move the pages; if this flag is not specified, then a subsequent splice(2)SPLICE_F_MOVE
must copy the pages. Data must also be properly page aligned, both in memory and length.
RETURN VALUE
Upon successful completion, vmsplice
() returns the number of bytes
transferred to the pipe. On error, vmsplice
() returns −1 and
errno
is set to indicate the
error.
ERRORS
- EAGAIN
-
SPLICE_F_NONBLOCK
was specified inflags
, and the operation would block. - EBADF
-
fd
either not valid, or doesn_zsingle_quotesz_t refer to a pipe. - EINVAL
-
nr_segs
is greater thanIOV_MAX
; or memory not aligned ifSPLICE_F_GIFT
set. - ENOMEM
-
Out of memory.
VERSIONS
The vmsplice
() system call
first appeared in Linux 2.6.17; library support was added to
glibc in version 2.5.
NOTES
vmsplice
() follows the other
vectorized read/write type functions when it comes to
limitations on the number of segments being passed in. This
limit is IOV_MAX
as defined in
<
limits.h
>
Currently, this limit is 1024.
vmsplice
() really supports
true splicing only from user memory to a pipe. In the
opposite direction, it actually just copies the data to
userspace. But this makes the interface nice and symmetric
and enables people to build on vmsplice
() with room for future improvement
in performance.
COLOPHON
This page is part of release 5.04 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
This manpage is Copyright (C) 2006 Jens Axboe and Copyright (C) 2006 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |