linux-kernel - [PATCH v2 02/12] csum_and_copy_to_iter(): handle ITER

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Date:   Fri, 28 Oct 2022 03:33:42 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     David Howells <dhowells@...hat.com>, willy@...radead.org,
        dchinner@...hat.com, Steve French <smfrench@...il.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>, torvalds@...ux-foundation.org,
        linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 02/12] csum_and_copy_to_iter(): handle ITER_DISCARD

Not hard to implement - we are not copying anything here, so
csum_and_memcpy() is not usable, but calculating a checksum
of source directly is trivial...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 lib/iov_iter.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index e9a8fc9ee8ee..020e009d71c5 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1549,8 +1549,12 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
 	__wsum sum, next;
 
 	if (unlikely(iov_iter_is_discard(i))) {
-		WARN_ON(1);	/* for now */
-		return 0;
+		// can't use csum_memcpy() for that one - data is not copied
+		csstate->csum = csum_block_add(csstate->csum,
+					       csum_partial(addr, bytes, 0),
+					       csstate->off);
+		csstate->off += bytes;
+		return bytes;
 	}
 
 	sum = csum_shift(csstate->csum, csstate->off);
-- 
2.30.2