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       vmsplice - splice user pages into a pipe


       #define _GNU_SOURCE
       #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

           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

       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, or 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.


       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.


       EBADF  fd either not valid, or doesn’t refer to a pipe.

       EINVAL nr_segs is 0 or 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.


       This system call is Linux-specific.


       vmsplice()  follows the other vectorized read/write type functions when
       it comes to limitations on number of segments being  passed  in.   This
       limit  is  IOV_MAX  as  defined  in  <limits.h>.   At  the time of this
       writing, that limit is 1024.


       splice(2), tee(2), feature_test_macros(7)


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