vmsplice(2) System Calls Manual vmsplice(2)
NAME
vmsplice - splice user pages to/from a pipe
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h>
ssize_t vmsplice(int fd, const struct iovec *iov,
size_t 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 described in
iovec(3type).
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 subse-
quent 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 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.
STANDARDS
Linux.
HISTORY
Linux 2.6.17, glibc 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
user space. But this makes the interface nice and symmetric and enables
people to build on vmsplice() with room for future improvement in per-
formance.
SEE ALSO
splice(2), tee(2), pipe(7)
Linux man-pages 6.9.1 2024-05-02 vmsplice(2)
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