xenial (2) vmsplice.2.gz

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

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