vmsplice() System Call in Linux

NAME

vmsplice - splice user pages into a pipe

SYNOPSIS

#define _GNU_SOURCE 
#include <fcntl.h> 
#include <sys/uio.h> 

long 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:

Tag	Description
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() SPLICE_F_MOVE can successfully move the pages; if this flag is not specified, then a subsequent splice() 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, vmplice() returns -1 and errno is set to indicate the error.

ERRORS

Tag	Description
EBADF	fd either not valid, or doesnt 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.

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.

HISTORY

The vmsplice(2) system call first appeared in Linux-2.6.17.

CONFORMING TO

This system call is Linux specific.