vmsplice

VMSPLICE(2)                Linux Programmer's Manual               VMSPLICE(2)

NAME
       vmsplice - splice user pages to/from a pipe

SYNOPSIS
       #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);

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 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 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.

VERSIONS
       The vmsplice() system call first appeared in Linux 2.6.17; library sup-
       port was added to glibc in version 2.5.

CONFORMING TO
       This system call is Linux-specific.

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
       userspace.  But this makes the interface nice and symmetric and enables
       people  to build on vmsplice() with room for future improvement in per-
       formance.

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

COLOPHON
       This page is part of release 5.05 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2019-03-06                       VMSPLICE(2)