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vmsplice() - Unix, Linux System Call

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vmsplice - splice user pages into a pipe


#define _GNU_SOURCE 
#include <fcntl.h> 
#include <sys/uio.h> 

long vmsplice(int fd, const struct iovec *iov, unsigned long nr_segs, unsigned int flags);


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, or page cache and on-disk data may differ. Gifting pages to the kernel means that a subsequent splice() SPLICE_F_MOVE can successfully move the pages; if this flag is not specified, then a subsequent splice() SPLICE_F_MOVE must copy the pages. Data must also be properly page aligned, both in memory and length.


Upon successful completion, vmsplice() returns the number of bytes transferred to the pipe. On error, vmplice() returns -1 and errno is set to indicate the error.


EBADF fd either not valid, or doesn’t refer to a pipe.
EINVAL nr_segs is 0 or greater than IOV_MAX; or memory not aligned if SPLICE_F_GIFT set.
ENOMEM Out of memory.


vmsplice() follows the other vectorized read/write type functions when it comes to limitations on number of segments being passed in. This limit is IOV_MAX as defined in <limits.h>. At the time of this writing, that limit is 1024.


The vmsplice(2) system call first appeared in Linux-2.6.17.


This system call is Linux specific.


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