vmsplice(2) — Linux manual pages

Linux manual pages	Section 2: System Calls

Name

vmsplice — splice user pages into 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

The vmsplice() system call maps nr_segs ranges of user memory described by iov into 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, or 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

EBADF: fd either not valid, or doesn't refer to a pipe.
EINVAL: nr_segs is 0 or greater than IOV_MAX; or memory not aligned if SPLICE_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.

CONFORMING TO

This system call is Linux-specific.

NOTES

vmsplice() follows the other vectorized read/write type functions when it comes to limitations on number of segments being passed in. This limit is IOV_MAX as defined in <limits.h> At the time of this writing, that limit is 1024.

COLOPHON

This page is part of release 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://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

struct	iovec {
	void	*	`iov_base`;	/* Starting address */
	size_t		`iov_len`;	/* Number of bytes */
};