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 subsequent 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 performance.

SEE ALSO

       splice(2), tee(2), pipe(7)