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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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VMSPLICE(2) Linux Programmer's Manual VMSPLICE(2)
vmsplice - splice user pages to/from a pipe
#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);
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.
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.
EAGAIN SPLICE_F_NONBLOCK was specified in flags, and the
operation would block.
EBADF fd either not valid, or doesn't refer to a pipe.
EINVAL nr_segs is greater than IOV_MAX; or memory not aligned if
SPLICE_F_GIFT set.
ENOMEM Out of memory.
The vmsplice() system call first appeared in Linux 2.6.17;
library support was added to glibc in version 2.5.
This system call is Linux-specific.
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.
splice(2), tee(2), pipe(7)
This page is part of release 5.10 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/.
Linux 2019-03-06 VMSPLICE(2)
Pages that refer to this page: pipe(2), splice(2), syscalls(2), tee(2), pipe(7)
Copyright and license for this manual page
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