vmsplice(2) — Linux manual page


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,
                        unsigned long 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

           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:

              Unused for vmsplice(); see splice(2).

              Do not block on I/O; see splice(2) for further details.

              Currently has no effect for vmsplice(), but may be implemented
              in the future; see splice(2).

              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
       userspace.  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 5.07 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

Linux                            2019-03-06                      VMSPLICE(2)

Pages that refer to this page: pipe2(2)pipe(2)splice(2)syscalls(2)tee(2)pipe(7)