vmsplice(2)                   System Calls Manual                  vmsplice(2)

NAME
       vmsplice - splice user pages to/from a pipe

LIBRARY
       Standard C library (libc, -lc)

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

       ssize_t vmsplice(int fd, const struct iovec *iov,
                        size_t 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 described in
       iovec(3type).

       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.

STANDARDS
       Linux.

HISTORY
       Linux 2.6.17, glibc 2.5.

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

Linux man-pages 6.7               2023-10-31                       vmsplice(2)