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;size_t iov_len;};
The flags argument
is a bit mask that is composed by ORing together zero or more
of the following values:
SPLICE_F_MOVEUnused for vmsplice();
see splice(2).
SPLICE_F_NONBLOCKDo not block on I/O; see splice(2) for further details.
SPLICE_F_MORECurrently has no effect for vmsplice(), but may be implemented in
the future; see splice(2).
SPLICE_F_GIFTThe 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(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.
fd either
not valid, or doesn't refer to a pipe.
nr_segs is 0
or greater than IOV_MAX;
or memory not aligned if SPLICE_F_GIFT set.
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.