From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 307DAC3A59D for ; Fri, 16 Aug 2019 22:21:44 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0194E2086C for ; Fri, 16 Aug 2019 22:21:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0194E2086C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60320 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hykbP-0000Je-4F for qemu-devel@archiver.kernel.org; Fri, 16 Aug 2019 18:21:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39545) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hykaO-0007fz-K0 for qemu-devel@nongnu.org; Fri, 16 Aug 2019 18:20:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hykaN-0002HF-GZ for qemu-devel@nongnu.org; Fri, 16 Aug 2019 18:20:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54610) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hykaL-0002Di-3M; Fri, 16 Aug 2019 18:20:37 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6D3748AC6F7; Fri, 16 Aug 2019 22:20:36 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-204-156.brq.redhat.com [10.40.204.156]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F361AF6C2; Fri, 16 Aug 2019 22:20:32 +0000 (UTC) To: John Snow References: From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <52b4cd48-93f2-c001-fa56-2fbd8485ee1d@redhat.com> Date: Sat, 17 Aug 2019 00:20:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="UGnLWZwmhbtxOyTMtxiU4boCtFAg4vl6O" X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.69]); Fri, 16 Aug 2019 22:20:36 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] bitmaps branch conflict resolution X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "qemu-devel@nongnu.org" , Qemu-block Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --UGnLWZwmhbtxOyTMtxiU4boCtFAg4vl6O Content-Type: multipart/mixed; boundary="NbcrPCYhKAhWyKCFfKcciG7hKehVKcJpB"; protected-headers="v1" From: Max Reitz To: John Snow Cc: Qemu-block , "qemu-devel@nongnu.org" Message-ID: <52b4cd48-93f2-c001-fa56-2fbd8485ee1d@redhat.com> Subject: Re: bitmaps branch conflict resolution References: In-Reply-To: --NbcrPCYhKAhWyKCFfKcciG7hKehVKcJpB Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 17.08.19 00:07, John Snow wrote: > Hi Max, I took your patch and adjusted it slightly: I don't like > "skip_bytes" anymore because it's clear now that we don't only read tha= t > value when we're skipping bytes, so now it's just status_bytes. Yep, sure. > Since this is based on your fixup, would you like to offer an > Ack/S-o-b/R-B/whichever here? Sure: Reviewed-by: Max Reitz Additional explanation for others: The conflict resolution in itself is just a matter of the =E2=80=9Cbackup_bitmap_reset_unallocated=E2=80=9D block and the =E2=80=9Cbdrv_dirty_bitmap_next_zero=E2=80=9D block introduced in the sam= e place in two separate patches (one went to master, the other to bitmaps-next). So the question is how to order them. On the first glance, it doesn=E2=80= =99t matter, it can go both ways. On a second glance, it turns out we need to combine the results, hence the new MIN() here. If we are initializing the bitmap, bdrv_dirty_bitmap_next_zero() does not necessarily return the correct result. It is only accurate insofar we have actually initialized the bitmap. We can get that information from backup_bitmap_reset_unallocated(): It ensures that the bitmap is accurate in the [start, start + status_bytes) range. Therefore, we have to limit dirty_end by start + status_bytes. I don=E2=80=99t think it really matters whether we do the backup_bitmap_reset_allocated() or the bdrv_dirty_bitmap_next_zero() first. It=E2=80=99s just that it=E2=80=99s slightly simpler to do the la= tter first, because the former is in a conditional block, so we can put the MIN() right there. Hence the order change here. (If we did it the other way around, we=E2=80=99d need another conditional= block =E2=80=9Cif (job->initializing_bitmap) { dirty_end =3D MIN(...) }=E2=80=9D= after we have both dirty_end and status_bytes.) Max > diff --git a/block/backup.c b/block/backup.c > index ee4d5598986..9e1382ec5c6 100644 > --- a/block/backup.c > +++ b/block/backup.c > @@ -266,7 +266,7 @@ static int coroutine_fn backup_do_cow(BackupBlockJo= b > *job, > int ret =3D 0; > int64_t start, end; /* bytes */ > void *bounce_buffer =3D NULL; > - int64_t skip_bytes; > + int64_t status_bytes; >=20 > qemu_co_rwlock_rdlock(&job->flush_rwlock); >=20 > @@ -287,21 +287,23 @@ static int coroutine_fn > backup_do_cow(BackupBlockJob *job, > continue; /* already copied */ > } >=20 > - if (job->initializing_bitmap) { > - ret =3D backup_bitmap_reset_unallocated(job, start, &skip_= bytes); > - if (ret =3D=3D 0) { > - trace_backup_do_cow_skip_range(job, start, skip_bytes)= ; > - start +=3D skip_bytes; > - continue; > - } > - } > - > dirty_end =3D bdrv_dirty_bitmap_next_zero(job->copy_bitmap, st= art, > (end - start)); > if (dirty_end < 0) { > dirty_end =3D end; > } >=20 > + if (job->initializing_bitmap) { > + ret =3D backup_bitmap_reset_unallocated(job, start, > &status_bytes); > + if (ret =3D=3D 0) { > + trace_backup_do_cow_skip_range(job, start, status_byte= s); > + start +=3D status_bytes; > + continue; > + } > + /* Clamp to known allocated region */ > + dirty_end =3D MIN(dirty_end, start + status_bytes); > + } > + > trace_backup_do_cow_process(job, start); >=20 > if (job->use_copy_range) { >=20 --NbcrPCYhKAhWyKCFfKcciG7hKehVKcJpB-- --UGnLWZwmhbtxOyTMtxiU4boCtFAg4vl6O Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl1XLC8ACgkQ9AfbAGHV z0ApXQgAvb+jKJ5WwUPNq291uZj5BiUztKofgxMLCscm/bLhfnhTGWnQljHQ4q8I 4piQS7bBgDVvgCRKGE+Wg/DPbLUHJrqwopgvkeSHrA4i/Bb+kxf63K/KZVkxFLL9 /NG6qnl1DBOjSdRoF5BAvTzpKNU4W0VshYMV9EYoslWZi6LJ8KZk3Dkhn4egvVl8 efK71LyT27plEO3FEGXbo3J0OHQ0s8De+EduJcIoolNnHTAerCcRn28rB8HIwpRc zKqNcACTDTi4brhYdFmRlpfQYb4qk4Ir+CkNH5YYowFQvxr7T6msuInObEZTNDkg iISvSXe3X+gdW3kWD5t4clEhhebSCA== =yLDs -----END PGP SIGNATURE----- --UGnLWZwmhbtxOyTMtxiU4boCtFAg4vl6O--