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iov_iter: optimize iov_iter_advance() for iovec and kvec 

We can do better than generic iterate_and_advance() for this one;
inspired by bvec_iter_advance() (and massaged into that form by
equivalent transformations).

[fixed a braino caught by kernel test robot <oliver.sang@intel.com>]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2021-04-23 12:58:53 -04:00
parent 8cd54c1c84
commit 185ac4d436
1 changed files with 28 additions and 14 deletions
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42
lib/iov_iter.c
View File

@ -1096,28 +1096,42 @@ static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
i->iov_offset = bi.bi_bvec_done;
}
static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
{
const struct iovec *iov, *end;
if (!i->count)
return;
i->count -= size;
size += i->iov_offset; // from beginning of current segment
for (iov = i->iov, end = iov + i->nr_segs; iov < end; iov++) {
if (likely(size < iov->iov_len))
break;
size -= iov->iov_len;
}
i->iov_offset = size;
i->nr_segs -= iov - i->iov;
i->iov = iov;
}
void iov_iter_advance(struct iov_iter *i, size_t size)
{
if (unlikely(i->count < size))
size = i->count;
if (unlikely(iov_iter_is_pipe(i))) {
if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
/* iovec and kvec have identical layouts */
iov_iter_iovec_advance(i, size);
} else if (iov_iter_is_bvec(i)) {
iov_iter_bvec_advance(i, size);
} else if (iov_iter_is_pipe(i)) {
pipe_advance(i, size);
return;
}
if (unlikely(iov_iter_is_discard(i))) {
i->count -= size;
return;
}
if (unlikely(iov_iter_is_xarray(i))) {
} else if (unlikely(iov_iter_is_xarray(i))) {
i->iov_offset += size;
i->count -= size;
return;
} else if (iov_iter_is_discard(i)) {
i->count -= size;
}
if (iov_iter_is_bvec(i)) {
iov_iter_bvec_advance(i, size);
return;
}
iterate_and_advance(i, size, v, 0, 0, 0, 0)
}
EXPORT_SYMBOL(iov_iter_advance);