Commit 3b2deb0e authored by Jens Axboe's avatar Jens Axboe
Browse files

iov_iter: import single vector iovecs as ITER_UBUF 



Add a special case to __import_iovec(), which imports a single segment
iovec as an ITER_UBUF rather than an ITER_IOVEC. ITER_UBUF is cheaper
to iterate than ITER_IOVEC, and for a single segment iovec, there's no
point in using a segmented iterator.

Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent e03ad4ee

lib/iov_iter.c

+27 −0
Original line number Diff line number Diff line
@@ -1784,6 +1784,30 @@ struct iovec *iovec_from_user(const struct iovec __user *uvec, 
	return iov;

}



/*

 * Single segment iovec supplied by the user, import it as ITER_UBUF.

 */

static ssize_t __import_iovec_ubuf(int type, const struct iovec __user *uvec,

				   struct iovec **iovp, struct iov_iter *i,

				   bool compat)

{

	struct iovec *iov = *iovp;

	ssize_t ret;



	if (compat)

		ret = copy_compat_iovec_from_user(iov, uvec, 1);

	else

		ret = copy_iovec_from_user(iov, uvec, 1);

	if (unlikely(ret))

		return ret;



	ret = import_ubuf(type, iov->iov_base, iov->iov_len, i);

	if (unlikely(ret))

		return ret;

	*iovp = NULL;

	return i->count;

}



ssize_t __import_iovec(int type, const struct iovec __user *uvec,

		 unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,

		 struct iov_iter *i, bool compat)
@@ -1792,6 +1816,9 @@ ssize_t __import_iovec(int type, const struct iovec __user *uvec, 
	unsigned long seg;

	struct iovec *iov;



	if (nr_segs == 1)

		return __import_iovec_ubuf(type, uvec, iovp, i, compat);



	iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);

	if (IS_ERR(iov)) {

		*iovp = NULL;