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VMSPLICE(2) Linux Programmer's Manual 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 sup-
     port 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.