vmsplice - splice user pages to/from a pipe

#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);

If fd is opened for writing, the vmsplice() system call maps nr_segs ranges of user memory described by iov into a pipe. If fd is opened for reading, the vmsplice() system call fills nr_segs 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 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.

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.

splice(2), tee(2), pipe(7)