From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35085) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFsdE-0001Kb-3X for qemu-devel@nongnu.org; Wed, 22 Jun 2016 20:36:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bFsdC-0004mp-7W for qemu-devel@nongnu.org; Wed, 22 Jun 2016 20:36:31 -0400 Date: Thu, 23 Jun 2016 08:36:17 +0800 From: Fam Zheng Message-ID: <20160623003617.GA17307@ad.usersys.redhat.com> References: <1466625064-11280-1-git-send-email-jsnow@redhat.com> <1466625064-11280-2-git-send-email-jsnow@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1466625064-11280-2-git-send-email-jsnow@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/3] mirror: clarify mirror_do_read return code List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow Cc: qemu-block@nongnu.org, kwolf@redhat.com, jcody@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com On Wed, 06/22 15:51, John Snow wrote: > mirror_do_read intends to return the number of sectors processed after > the starting sector, without regard to how many sectors were processed > before the starting sector due to alignment. > > Clean up the comments and code to hopefully illustrate this more clearly. > > This also fixes an issue in initialization where if the mirror buffer size > is initialized to smaller than the number of sectors being requested for > transfer, we report back an incorrectly large number to the caller. Good catch! Reviewed-by: Fam Zheng > > Signed-off-by: John Snow > --- > block/mirror.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/block/mirror.c b/block/mirror.c > index a04ed9c..2ba9642 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -218,7 +218,9 @@ static inline void mirror_wait_for_io(MirrorBlockJob *s) > } > > /* Submit async read while handling COW. > - * Returns: nb_sectors if no alignment is necessary, or > + * Returns: The number of sectors copied after and including sector_num, > + * excluding any sectors copied prior to sector_num due to alignment. > + * This will be nb_sectors if no alignment is necessary, or > * (new_end - sector_num) if tail is rounded up or down due to > * alignment or buffer limit. > */ > @@ -227,7 +229,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num, > { > BlockBackend *source = s->common.blk; > int sectors_per_chunk, nb_chunks; > - int ret = nb_sectors; > + int ret; > MirrorOp *op; > > sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS; > @@ -235,6 +237,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num, > /* We can only handle as much as buf_size at a time. */ > nb_sectors = MIN(s->buf_size >> BDRV_SECTOR_BITS, nb_sectors); > assert(nb_sectors); > + ret = nb_sectors; > > if (s->cow_bitmap) { > ret += mirror_cow_align(s, §or_num, &nb_sectors); > -- > 2.4.11 >