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SPLICE(2)		   Linux Programmers Manual		    SPLICE(2)

       splice - splice data to/from a pipe

       #define _GNU_SOURCE

       long 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.

       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 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 dont refer to full pages.

       SPLICE_F_NONBLOCK  Do  not  block  on  I/O.  This makes the splice pipe
			  operations non-blocking, but splice() may  neverthe
			  less	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.

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

       EINVAL Target  file  system  doesnt  support  splicing; neither of the
	      descriptors refers to a pipe; or offset given  for  non-seekable

       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.

       This system call is Linux-specific.

       The three system  calls	splice(),  vmsplice(2),  and  tee(2),  provide
       userspace  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

       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), feature_test_macros(7)

       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2008-01-31			     SPLICE(2)

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