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       vmsplice - splice user pages into a pipe


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

       ssize_t vmsplice(int fd, const struct iovec *iov,
                        unsigned long nr_segs, unsigned int flags);


       The  vmsplice()  system  call  maps  nr_segs ranges of user memory described by iov into a
       pipe.  The file descriptor fd must refer to a pipe.

       The pointer iov points to an array of iovec structures as defined in <sys/uio.h>:

           struct iovec {
               void  *iov_base;        /* Starting address */
               size_t iov_len;         /* Number of bytes */

       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


       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.


       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.


       The  vmsplice()  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.


       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.


       splice(2), tee(2)


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