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: Jens Axboe <axboe@xxxxxxxxx>
---
lib/iov_iter.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index fc82cc42ffe6..63cf9997bd50 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1780,6 +1780,30 @@ 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)
@@ -1788,6 +1812,9 @@ 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;
--
2.39.2
