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.\" This manpage is Copyright (C) 2006 Jens Axboe
.\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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-.TH SPLICE 2 2006-04-28 "Linux" "Linux Programmer's Manual"
+.TH SPLICE 2 2019-05-09 "Linux" "Linux Programmer's Manual"
.SH NAME
splice \- splice data to/from a pipe
.SH SYNOPSIS
.nf
-.B #define _GNU_SOURCE
+.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
.B #include <fcntl.h>
-
-.BI "long splice(int " fd_in ", off_t *" off_in ", int " fd_out ,
-.BI " off_t *" off_out ", size_t " len \
+.PP
+.BI "ssize_t splice(int " fd_in ", loff_t *" off_in ", int " fd_out ,
+.BI " loff_t *" off_out ", size_t " len \
", unsigned int " flags );
+.\" Return type was long before glibc 2.7
.fi
.SH DESCRIPTION
.BR splice ()
.I fd_in
to the file descriptor
.IR fd_out ,
-where one of the descriptors must refer to a pipe.
-
+where one of the file descriptors must refer to a pipe.
+.PP
+The following semantics apply for
+.I fd_in
+and
+.IR off_in :
+.IP * 3
If
.I fd_in
refers to a pipe, then
.I off_in
must be NULL.
+.IP *
If
.I fd_in
does not refer to a pipe and
.I off_in
is NULL, then bytes are read from
.I fd_in
-starting from the current file offset,
-and the current file offset is adjusted appropriately.
+starting from the file offset,
+and the file offset is adjusted appropriately.
+.IP *
If
.I fd_in
does not refer to a pipe and
must point to a buffer which specifies the starting
offset from which bytes will be read from
.IR fd_in ;
-in this case, the current file offset of
+in this case, the file offset of
.I fd_in
is not changed.
+.PP
Analogous statements apply for
.I fd_out
and
.IR off_out .
-
+.PP
The
.I flags
argument is a bit mask that is composed by ORing together
zero or more of the following values:
-.TP 1.9i
+.TP
.B 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
+.BR splice ()
+call);
+in the future, a correct implementation may be restored.
.TP
.B SPLICE_F_NONBLOCK
Do not block on I/O.
-This makes the splice pipe operations non-blocking, but
+This makes the splice pipe operations nonblocking, but
.BR splice ()
may nevertheless block because the file descriptors that
are spliced to/from may block (unless they have the
and the description of
.B TCP_CORK
in
-.BR tcp (7))
+.BR tcp (7)).
.TP
.B SPLICE_F_GIFT
Unused for
.BR 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
-.IR fd_in .
-
+.PP
+A return value of 0 means end of input.
+If
+.I fd_in
+refers to a pipe, then this 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.
+.PP
On error,
.BR splice ()
returns \-1 and
is set to indicate the error.
.SH ERRORS
.TP
+.B EAGAIN
+.B SPLICE_F_NONBLOCK
+was specified in
+.IR flags
+or one of the file descriptors had been marked as nonblocking
+.RB ( O_NONBLOCK ) ,
+and the operation would block.
+.TP
.B EBADF
One or both file descriptors are not valid,
or do not have proper read-write mode.
.TP
.B EINVAL
-Target file system doesn't support splicing;
-neither of the descriptors refers to a pipe; or
-offset given for non-seekable device.
+The target filesystem doesn't support splicing.
+.TP
+.B EINVAL
+The target file is opened in append mode.
+.\" The append-mode error is given since 2.6.27; in earlier kernels,
+.\" splice() in append mode was broken
+.TP
+.B EINVAL
+Neither of the file descriptors refers to a pipe.
+.TP
+.B EINVAL
+An offset was given for nonseekable device (e.g., a pipe).
+.TP
+.B EINVAL
+.I fd_in
+and
+.I fd_out
+refer to the same pipe.
.TP
.B ENOMEM
Out of memory.
.SH VERSIONS
The
.BR splice ()
-system call first appeared in Linux 2.6.17.
-.SH "CONFORMING TO"
+system call first appeared in Linux 2.6.17;
+library support was added to glibc in version 2.5.
+.SH CONFORMING TO
This system call is Linux-specific.
.SH NOTES
The three system calls
.BR vmsplice (2),
and
.BR tee (2),
-provide userspace programs with full control over an arbitrary
+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 following tasks:
.\" the data and choose to forward it to two or more different
.\" users - for things like logging etc.).
.\"
+.PP
+In Linux 2.6.30 and earlier,
+exactly one of
+.I fd_in
+and
+.I fd_out
+was required to be a pipe.
+Since Linux 2.6.31,
+.\" commit 7c77f0b3f9208c339a4b40737bb2cb0f0319bb8d
+both arguments may refer to pipes.
.SH EXAMPLE
See
.BR tee (2).
.SH SEE ALSO
+.BR copy_file_range (2),
.BR sendfile (2),
.BR tee (2),
.BR vmsplice (2),
-.BR feature_test_macros (7)
+.BR pipe (7)
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