From: Al Viro <viro@zeniv.linux.org.uk>
To: David Laight <David.Laight@aculab.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 04/18] csum_and_copy_..._user(): pass 0xffffffff instead of 0 as initial sum
Date: Wed, 22 Jul 2020 15:42:13 +0100 [thread overview]
Message-ID: <20200722144213.GE2786714@ZenIV.linux.org.uk> (raw)
In-Reply-To: <2d85ebb8ea2248c8a14f038a0c60297e@AcuMS.aculab.com>
On Wed, Jul 22, 2020 at 09:27:32AM +0000, David Laight wrote:
> 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 <viro@zeniv.linux.org.uk>
> > ---
> > 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).
And the benefit of that would be...? It wouldn't be any simpler,
it almost certainly would not even be a valid microoptimization
(nevermind that this is an arch-independent code)...
next prev parent reply other threads:[~2020-07-22 14:42 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 20:24 [RFC][CFT][PATCHSET] saner calling conventions for csum-and-copy primitives Al Viro
2020-07-21 20:25 ` [PATCH 01/18] skb_copy_and_csum_bits(): don't bother with the last argument Al Viro
2020-07-21 20:25 ` [PATCH 02/18] icmp_push_reply(): reorder adding the checksum up Al Viro
2020-07-21 20:25 ` [PATCH 03/18] csum_partial_copy_nocheck(): drop the last argument Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 04/18] csum_and_copy_..._user(): pass 0xffffffff instead of 0 as initial sum Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:55 ` Linus Torvalds
2020-07-21 20:58 ` Linus Torvalds
2020-07-21 21:11 ` Al Viro
2020-07-21 21:16 ` Linus Torvalds
2020-07-21 21:16 ` Linus Torvalds
2020-07-25 17:54 ` Al Viro
2020-07-22 9:45 ` David Laight
2020-07-22 9:27 ` David Laight
2020-07-22 14:42 ` Al Viro [this message]
2020-07-22 15:22 ` David Laight
2020-07-22 15:54 ` Al Viro
2020-07-22 16:17 ` David Laight
2020-07-22 17:39 ` Al Viro
2020-07-23 8:29 ` David Laight
2020-07-23 13:54 ` David Laight
2020-07-23 14:30 ` David Laight
2020-07-23 14:53 ` Al Viro
2020-07-23 15:19 ` David Laight
2020-07-23 15:21 ` Al Viro
2020-07-23 15:36 ` David Laight
2020-07-21 20:25 ` [PATCH 05/18] saner calling conventions for csum_and_copy_..._user() Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 06/18] alpha: propagate the calling convention changes down to csum_partial_copy.c helpers Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 07/18] arm: propagate the calling convention changes down to csum_partial_copy_from_user() Al Viro
2020-07-21 20:25 ` [PATCH 08/18] m68k: get rid of zeroing destination on error in csum_and_copy_from_user() Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 09/18] sh: propage the calling conventions change down to csum_partial_copy_generic() Al Viro
2020-07-21 20:25 ` [PATCH 10/18] i386: propagate " Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 11/18] sparc32: propagate the calling conventions change down to __csum_partial_copy_sparc_generic() Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-22 1:20 ` David Miller
2020-07-21 20:25 ` [PATCH 12/18] mips: csum_and_copy_{to,from}_user() are never called under KERNEL_DS Al Viro
2020-07-21 20:25 ` [PATCH 13/18] mips: __csum_partial_copy_kernel() has no users left Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 14/18] mips: propagate the calling convention change down into __csum_partial_copy_..._user() Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 15/18] xtensa: propagate the calling conventions change down into csum_partial_copy_generic() Al Viro
2020-07-22 8:56 ` Max Filippov
2020-07-21 20:25 ` [PATCH 16/18] sparc64: propagate the calling convention changes down to __csum_partial_copy_...() Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-22 1:21 ` David Miller
2020-07-21 20:25 ` [PATCH 17/18] amd64: switch csum_partial_copy_generic() to new calling conventions Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-21 20:25 ` [PATCH 18/18] ppc: propagate the calling conventions change down to csum_partial_copy_generic() Al Viro
2020-07-21 20:25 ` Al Viro
2020-07-24 1:25 ` [RFC][CFT][PATCHSET v2] saner calling conventions for csum-and-copy primitives Al Viro
2020-07-24 1:25 ` [PATCH v2 01/20] xtensa: fix access check in csum_and_copy_from_user Al Viro
2020-07-24 1:25 ` [PATCH v2 02/20] skb_copy_and_csum_bits(): don't bother with the last argument Al Viro
2020-07-24 1:25 ` [PATCH v2 03/20] icmp_push_reply(): reorder adding the checksum up Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 04/20] unify generic instances of csum_partial_copy_nocheck() Al Viro
2020-07-24 6:41 ` Christoph Hellwig
2020-07-24 12:19 ` Al Viro
2020-07-24 12:23 ` Christoph Hellwig
2020-07-24 12:30 ` Al Viro
2020-07-26 7:11 ` Christoph Hellwig
2020-07-26 7:11 ` Christoph Hellwig
2020-07-27 3:58 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 05/20] csum_partial_copy_nocheck(): drop the last argument Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 06/20] csum_and_copy_..._user(): pass 0xffffffff instead of 0 as initial sum Al Viro
2020-07-24 1:25 ` [PATCH v2 07/20] saner calling conventions for csum_and_copy_..._user() Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 08/20] alpha: propagate the calling convention changes down to csum_partial_copy.c helpers Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 09/20] arm: propagate the calling convention changes down to csum_partial_copy_from_user() Al Viro
2020-07-24 1:25 ` [PATCH v2 10/20] m68k: get rid of zeroing destination on error in csum_and_copy_from_user() Al Viro
2020-07-24 1:25 ` [PATCH v2 11/20] sh: propage the calling conventions change down to csum_partial_copy_generic() Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 12/20] i386: propagate " Al Viro
2020-07-24 1:25 ` [PATCH v2 13/20] sparc32: propagate the calling conventions change down to __csum_partial_copy_sparc_generic() Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 14/20] mips: csum_and_copy_{to,from}_user() are never called under KERNEL_DS Al Viro
2020-07-24 1:25 ` [PATCH v2 15/20] mips: __csum_partial_copy_kernel() has no users left Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 16/20] mips: propagate the calling convention change down into __csum_partial_copy_..._user() Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 17/20] xtensa: propagate the calling conventions change down into csum_partial_copy_generic() Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 18/20] sparc64: propagate the calling convention changes down to __csum_partial_copy_...() Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 19/20] amd64: switch csum_partial_copy_generic() to new calling conventions Al Viro
2020-07-24 1:25 ` Al Viro
2020-07-24 1:25 ` [PATCH v2 20/20] ppc: propagate the calling conventions change down to csum_partial_copy_generic() Al Viro
2020-07-24 1:25 ` Al Viro
2020-10-14 22:26 ` Jason A. Donenfeld
2020-10-14 22:51 ` Linus Torvalds
2020-10-14 22:53 ` Linus Torvalds
2020-10-14 22:54 ` Jason A. Donenfeld
2020-10-14 22:53 ` Jason A. Donenfeld
2020-10-14 23:12 ` Al Viro
2020-10-14 23:02 ` [PATCH] powerpc32: don't adjust unmoved stack pointer in csum_partial_copy_generic() epilogue Jason A. Donenfeld
2020-10-14 23:05 ` Linus Torvalds
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