vmsplice(2) - Linux manual page (original) (raw)

vmsplice(2) System Calls Manual vmsplice(2)

NAME top

   vmsplice - splice user pages to/from a pipe

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

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

   **ssize_t vmsplice(int** _fd_**, const struct iovec ***_iov_**,**
                    **size_t** _nrsegs_**, unsigned int** _flags_**);**

DESCRIPTION top

   If _fd_ is opened for writing, the **vmsplice**() system call maps
   _nrsegs_ ranges of user memory described by _iov_ into a pipe.  If _fd_
   is opened for reading, the **vmsplice**() system call fills _nrsegs_
   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)](../man3/iovec.3type.html).

   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)](../man2/splice.2.html).

   **SPLICE_F_NONBLOCK**
          Do not block on I/O; see [splice(2)](../man2/splice.2.html) for further details.

   **SPLICE_F_MORE**
          Currently has no effect for **vmsplice**(), but may be
          implemented in the future; see [splice(2)](../man2/splice.2.html).

   **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)](../man2/splice.2.html) **SPLICE_F_MOVE** can
          successfully move the pages; if this flag is not specified,
          then a subsequent [splice(2)](../man2/splice.2.html) **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](../man3/errno.3.html)_ 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** _nrsegs_ is greater than **IOV_MAX**; or memory not aligned if
          **SPLICE_F_GIFT** set.

   **ENOMEM** Out of memory.

STANDARDS top

   Linux.

HISTORY top

   Linux 2.6.17, glibc 2.5.

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)](../man2/splice.2.html), [tee(2)](../man2/tee.2.html), [pipe(7)](../man7/pipe.7.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 vmsplice(2)

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