vmsplice(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       vmsplice - splice user pages to/from a pipe

SYNOPSIS         top

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

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

DESCRIPTION         top

       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         top

       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         top

       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         top

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

CONFORMING TO         top

       This system call is Linux-specific.

NOTES         top

       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         top

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

COLOPHON         top

       This page is part of release 5.11 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                          2021-03-22                    VMSPLICE(2)

Pages that refer to this page: pipe(2)splice(2)syscalls(2)tee(2)pipe(7)