SPLICE(2) Linux Programmer's Manual SPLICE(2)
splice - splice data to/from a pipe
#define _GNU_SOURCE /* See feature_test_macros(7) */
ssize_t splice(int fd_in, loff_t *off_in, int fd_out,
loff_t *off_out, size_t len, unsigned int flags);
splice() moves data between two file descriptors without copying between kernel address
space and user address space. It transfers up to len bytes of data from the file descrip-
tor fd_in to the file descriptor fd_out, where one of the descriptors must refer to a
If fd_in refers to a pipe, then off_in must be NULL. If fd_in does not refer to a pipe
and off_in is NULL, then bytes are read from fd_in starting from the current file offset,
and the current file offset is adjusted appropriately. If fd_in does not refer to a pipe
and off_in is not NULL, then off_in must point to a buffer which specifies the starting
offset from which bytes will be read from fd_in; in this case, the current file offset of
fd_in is not changed. Analogous statements apply for fd_out and off_out.
The flags argument is a bit mask that is composed by ORing together zero or more of the
SPLICE_F_MOVE Attempt to move pages instead of copying. This is only a hint to the
kernel: pages may still be copied if the kernel cannot move the pages
from the pipe, or if the pipe buffers don't refer to full pages. The
initial implementation of this flag was buggy: therefore starting in
Linux 2.6.21 it is a no-op (but is still permitted in a splice() call);
in the future, a correct implementation may be restored.
SPLICE_F_NONBLOCK Do not block on I/O. This makes the splice pipe operations nonblock-
ing, but splice() may nevertheless block because the file descriptors
that are spliced to/from may block (unless they have the O_NONBLOCK
SPLICE_F_MORE More data will be coming in a subsequent splice. This is a helpful
hint when the fd_out refers to a socket (see also the description of
MSG_MORE in send(2), and the description of TCP_CORK in tcp(7))
SPLICE_F_GIFT Unused for splice(); see vmsplice(2).
Upon successful completion, splice() returns the number of bytes spliced to or from the
pipe. A return value of 0 means that there was no data to transfer, and it would not make
sense to block, because there are no writers connected to the write end of the pipe
referred to by fd_in.
On error, splice() returns -1 and errno is set to indicate the error.
EBADF One or both file descriptors are not valid, or do not have proper read-write mode.
EINVAL Target file system doesn't support splicing; target file is opened in append mode;
neither of the descriptors refers to a pipe; or offset given for nonseekable
ENOMEM Out of memory.
ESPIPE Either off_in or off_out was not NULL, but the corresponding file descriptor refers
to a pipe.
The splice() 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.
The three system calls splice(), vmsplice(2), and tee(2), provide user-space programs with
full control over an arbitrary kernel buffer, implemented within the kernel using the same
type of buffer that is used for a pipe. In overview, these system calls perform the fol-
splice() moves data from the buffer to an arbitrary file descriptor, or vice versa, or
from one buffer to another.
tee(2) "copies" the data from one buffer to another.
vmsplice(2) "copies" data from user space into the buffer.
Though we talk of copying, actual copies are generally avoided. The kernel does this by
implementing a pipe buffer as a set of reference-counted pointers to pages of kernel mem-
ory. The kernel creates "copies" of pages in a buffer by creating new pointers (for the
output buffer) referring to the pages, and increasing the reference counts for the pages:
only pointers are copied, not the pages of the buffer.
sendfile(2), tee(2), vmsplice(2)
This page is part of release 3.53 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
Linux 2012-05-04 SPLICE(2)