Open Source Software

vmsplice(2)



NAME

   vmsplice - splice user pages into 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

   The vmsplice() system call maps nr_segs ranges of user memory described
   by iov into 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
   support 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.

SEE ALSO

   splice(2), tee(2)

COLOPHON

   This page is part of release 4.09 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/.



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