Provided by: manpages-dev_4.04-2_all bug


       splice - splice data to/from a pipe


       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <fcntl.h>

       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
       descriptor fd_in to the file descriptor fd_out, where one of the descriptors must refer to
       a pipe.

       The following semantics apply for fd_in and off_in:

       *  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

       *  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
       following values:

       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
                          nonblocking,  but  splice()  may  nevertheless  block  because the file
                          descriptors that are spliced to/from may block (unless  they  have  the
                          O_NONBLOCK flag set).

       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.


       EAGAIN SPLICE_F_NONBLOCK was specified in flags, and the operation would block.

       EBADF  One or both file descriptors are not valid, or do not have proper read-write mode.

       EINVAL Target filesystem 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
       following tasks:

       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
       memory.  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.


       See tee(2).


       sendfile(2), tee(2), vmsplice(2)


       This page is part of release 4.04 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