linux-kernel - [RFC PATCH 34/37] iov_iter: clean csum_and_copy

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Date:   Sun,  6 Jun 2021 19:10:48 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Sterba <dsterba@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Anton Altaparmakov <anton@...era.com>,
        David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC PATCH 34/37] iov_iter: clean csum_and_copy_...() primitives up a bit

1) kmap_atomic() is not needed here, kmap_local_page() is enough.
2) No need to make sum = csum_block_add(sum, next, off); conditional
upon next != 0 - adding 0 is a no-op as far as csum_block_add()
is concerned.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 lib/iov_iter.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 0a9e246178c1..56d2606a47e4 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -611,9 +611,9 @@ static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
 		return 0;
 	do {
 		size_t chunk = min_t(size_t, n, PAGE_SIZE - r);
-		char *p = kmap_atomic(pipe->bufs[i_head & p_mask].page);
+		char *p = kmap_local_page(pipe->bufs[i_head & p_mask].page);
 		sum = csum_and_memcpy(p + r, addr, chunk, sum, off);
-		kunmap_atomic(p);
+		kunmap_local(p);
 		i->head = i_head;
 		i->iov_offset = r + chunk;
 		n -= chunk;
@@ -1678,8 +1678,7 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
 	}
 	iterate_and_advance(i, bytes, base, len, off, ({
 		next = csum_and_copy_from_user(base, addr + off, len);
-		if (next)
-			sum = csum_block_add(sum, next, off);
+		sum = csum_block_add(sum, next, off);
 		next ? 0 : len;
 	}), ({
 		sum = csum_and_memcpy(addr + off, base, len, sum, off);
@@ -1706,8 +1705,7 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
 	}
 	iterate_and_advance(i, bytes, base, len, off, ({
 		next = csum_and_copy_to_user(addr + off, base, len);
-		if (next)
-			sum = csum_block_add(sum, next, off);
+		sum = csum_block_add(sum, next, off);
 		next ? 0 : len;
 	}), ({
 		sum = csum_and_memcpy(base, addr + off, len, sum, off);
-- 
2.11.0