From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Subject: RE: [PATCH 04/18] csum_and_copy_..._user(): pass 0xffffffff instead of 0 as initial sum Date: Wed, 22 Jul 2020 09:27:32 +0000 Message-ID: <2d85ebb8ea2248c8a14f038a0c60297e@AcuMS.aculab.com> References: <20200721202425.GA2786714@ZenIV.linux.org.uk> <20200721202549.4150745-1-viro@ZenIV.linux.org.uk> <20200721202549.4150745-4-viro@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Return-path: Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:24819 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726153AbgGVJ1h (ORCPT ); Wed, 22 Jul 2020 05:27:37 -0400 In-Reply-To: <20200721202549.4150745-4-viro@ZenIV.linux.org.uk> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org List-ID: To: 'Al Viro' , Linus Torvalds Cc: "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" From: Al Viro > Sent: 21 July 2020 21:26 > Preparation for the change of calling conventions; right now all > callers pass 0 as initial sum. Passing 0xffffffff instead yields > the values comparable mod 0xffff and guarantees that 0 will not > be returned on success. > > Signed-off-by: Al Viro > --- > lib/iov_iter.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index 7405922caaec..d5b7e204fea6 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -1451,7 +1451,7 @@ size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum, > int err = 0; > next = csum_and_copy_from_user(v.iov_base, > (to += v.iov_len) - v.iov_len, > - v.iov_len, 0, &err); > + v.iov_len, ~0U, &err); > if (!err) { > sum = csum_block_add(sum, next, off); > off += v.iov_len; Can't you remove the csum_block_add() by passing the old 'sum' in instead of the ~0U ? You'll need to keep track of whether the buffer fragment is odd/even aligned. After an odd length fragment a bswap32() or 8 bit rotate will fix things (and maybe one right at the end). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)