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Mon, 9 Dec 2019 14:43:54 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.36.118.51]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 01FDF5D6C5; Mon, 9 Dec 2019 14:43:52 +0000 (UTC) Subject: Re: [PATCH for-5.0 v2 15/23] mirror: Prevent loops To: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" References: <20191111160216.197086-1-mreitz@redhat.com> <20191111160216.197086-16-mreitz@redhat.com> <7f50c050-38ca-a7f2-361b-a08e82b420af@virtuozzo.com> From: Max Reitz 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: Date: Mon, 9 Dec 2019 15:43:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <7f50c050-38ca-a7f2-361b-a08e82b420af@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="QGrMx2ztDsGRJL1YnJBsQV7e9AodTSSRi" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 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: Kevin Wolf , Alberto Garcia , "qemu-devel@nongnu.org" 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) --QGrMx2ztDsGRJL1YnJBsQV7e9AodTSSRi Content-Type: multipart/mixed; boundary="M3LzYkEBB7aVpGYXfvW2GGHzGhZS6e4kc" --M3LzYkEBB7aVpGYXfvW2GGHzGhZS6e4kc Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 02.12.19 13:12, Vladimir Sementsov-Ogievskiy wrote: > 11.11.2019 19:02, Max Reitz wrote: >> While bdrv_replace_node() will not follow through with it, a specific >> @replaces asks the mirror job to create a loop. >> >> For example, say both the source and the target share a child where the >> source is a filter; by letting @replaces point to the common child, you >> ask for a loop. >> >> Or if you use @replaces in drive-mirror with sync=3Dnone and >> mode=3Dabsolute-paths, you generally ask for a loop (@replaces must poin= t >> to a child of the source, and sync=3Dnone makes the source the backing >> file of the target after the job). >> >> bdrv_replace_node() will not create those loops, but by doing so, it >> ignores the user-requested configuration, which is not ideally either. >> (In the first example above, the target's child will remain what it was, >> which may still be reasonable. But in the second example, the target >> will just not become a child of the source, which is precisely what was >> requested with @replaces.) >> >> So prevent such configurations, both before the job, and before it >> actually completes. >> >> Signed-off-by: Max Reitz >> --- >> block.c | 30 ++++++++++++++++++++++++ >> block/mirror.c | 19 +++++++++++++++- >> blockdev.c | 48 ++++++++++++++++++++++++++++++++++++++- >> include/block/block_int.h | 3 +++ >> 4 files changed, 98 insertions(+), 2 deletions(-) >> >> diff --git a/block.c b/block.c >> index 0159f8e510..e3922a0474 100644 >> --- a/block.c >> +++ b/block.c >> @@ -6259,6 +6259,36 @@ out: >> return to_replace_bs; >> } >> =20 >> +/* >> + * Return true iff @child is a (recursive) child of @parent, with at >> + * least @min_level edges between them. >> + * >> + * (If @min_level =3D=3D 0, return true if @child =3D=3D @parent. For >> + * @min_level =3D=3D 1, @child needs to be at least a real child; for >> + * @min_level =3D=3D 2, it needs to be at least a grand-child; and so o= n.) >> + */ >> +bool bdrv_is_child_of(BlockDriverState *child, BlockDriverState *parent= , >> + int min_level) >> +{ >> + BdrvChild *c; >> + >> + if (child =3D=3D parent && min_level <=3D 0) { >> + return true; >> + } >> + >> + if (!parent) { >> + return false; >> + } >> + >> + QLIST_FOREACH(c, &parent->children, next) { >> + if (bdrv_is_child_of(child, c->bs, min_level - 1)) { >> + return true; >> + } >> + } >> + >> + return false; >> +} >> + >> /** >> * Iterates through the list of runtime option keys that are said to >> * be "strong" for a BDS. An option is called "strong" if it changes >> diff --git a/block/mirror.c b/block/mirror.c >> index 68a4404666..b258c7e98b 100644 >> --- a/block/mirror.c >> +++ b/block/mirror.c >> @@ -701,7 +701,24 @@ static int mirror_exit_common(Job *job) >> * there. >> */ >> if (bdrv_recurse_can_replace(src, to_replace)) { >> - bdrv_replace_node(to_replace, target_bs, &local_err); >> + /* >> + * It is OK for @to_replace to be an immediate child of >> + * @target_bs, because that is what happens with >> + * drive-mirror sync=3Dnone mode=3Dabsolute-paths: target_b= s's >> + * backing file will be the source node, which is also >> + * to_replace (by default). >> + * bdrv_replace_node() handles this case by not letting >> + * target_bs->backing point to itself, but to the source >> + * still. >> + */ >> + if (!bdrv_is_child_of(to_replace, target_bs, 2)) { >> + bdrv_replace_node(to_replace, target_bs, &local_err); >> + } else { >> + error_setg(&local_err, "Can no longer replace '%s' by '= %s', " >> + "because the former is now a child of the la= tter, " >> + "and doing so would thus create a loop", >> + to_replace->node_name, target_bs->node_name)= ; >> + } >=20 > you may swap if and else branch, dropping "!" mark.. Yes, but I just personally prefer to have the error case in the else branch= . >> } else { >> error_setg(&local_err, "Can no longer replace '%s' by '%s'= , " >> "because it can no longer be guaranteed that do= ing so " >> diff --git a/blockdev.c b/blockdev.c >> index 9dc2238bf3..d29f147f72 100644 >> --- a/blockdev.c >> +++ b/blockdev.c >> @@ -3824,7 +3824,7 @@ static void blockdev_mirror_common(const char *job= _id, BlockDriverState *bs, >> } >> =20 >> if (has_replaces) { >> - BlockDriverState *to_replace_bs; >> + BlockDriverState *to_replace_bs, *target_backing_bs; >> AioContext *replace_aio_context; >> int64_t bs_size, replace_size; >> =20 >> @@ -3839,6 +3839,52 @@ static void blockdev_mirror_common(const char *jo= b_id, BlockDriverState *bs, >> return; >> } >> =20 >> + if (bdrv_is_child_of(to_replace_bs, target, 1)) { >> + error_setg(errp, "Replacing %s by %s would result in a loop= , " >> + "because the former is a child of the latter", >> + to_replace_bs->node_name, target->node_name); >> + return; >> + } >=20 > here min_level=3D1, so we don't handle the case, described in mirror_exit= _common.. > I don't see why.. blockdev_mirror_common is called from qmp_drive_mirror, > including the case with MIRROR_SYNC_MODE_NONE and NEW_IMAGE_MODE_ABSOLUTE= _PATHS.. >=20 > What I'm missing? Hmm. Well. If it broke drive-mirror sync=3Dnone, I suppose I would have noticed by running the iotests. But I didn=92t, and that=92s because this code here i= s reached only if the user actually specified @replaces. (As opposed to the mirror_exit_common code, where @to_replace may simply be @src if not overridden by the user.) The only reason why I allow it in mirror_exit_common is because we have to. But if the user manually specifies this configuration, we can=92t guarantee it=92s safe. OTOH, well, if we allow it for drive-mirror sync=3Dnone, why not allow it when manually specified with blockdev-mirror? What=92s your opinion? >> + >> + if (backing_mode =3D=3D MIRROR_SOURCE_BACKING_CHAIN || >> + backing_mode =3D=3D MIRROR_OPEN_BACKING_CHAIN) >> + { >> + /* >> + * While we do not quite know what OPEN_BACKING_CHAIN >> + * (used for mode=3Dexisting) will yield, it is probably >> + * best to restrict it exactly like SOURCE_BACKING_CHAIN, >> + * because that is our best guess. >> + */ >> + switch (sync) { >> + case MIRROR_SYNC_MODE_FULL: >> + target_backing_bs =3D NULL; >> + break; >> + >> + case MIRROR_SYNC_MODE_TOP: >> + target_backing_bs =3D backing_bs(bs); >> + break; >> + >> + case MIRROR_SYNC_MODE_NONE: >> + target_backing_bs =3D bs; >> + break; >> + >> + default: >> + abort(); >> + } >> + } else { >> + assert(backing_mode =3D=3D MIRROR_LEAVE_BACKING_CHAIN); >> + target_backing_bs =3D backing_bs(target); >> + } >> + >> + if (bdrv_is_child_of(to_replace_bs, target_backing_bs, 0)) { >> + error_setg(errp, "Replacing '%s' by '%s' with this sync mod= e would " >> + "result in a loop, because the former would be a= child " >> + "of the latter's backing file ('%s') after the m= irror " >> + "job", to_replace_bs->node_name, target->node_na= me, >> + target_backing_bs->node_name); >> + return; >> + } >=20 > hmm.. so for MODE_NONE we disallow to_replace =3D=3D src? I suppose that=92s basically the same as above. Should we allow this case when specified explicitly by the user? Max >> + >> replace_aio_context =3D bdrv_get_aio_context(to_replace_bs); >> aio_context_acquire(replace_aio_context); >> replace_size =3D bdrv_getlength(to_replace_bs); >> diff --git a/include/block/block_int.h b/include/block/block_int.h >> index 589a797fab..7064a1a4fa 100644 >> --- a/include/block/block_int.h >> +++ b/include/block/block_int.h >> @@ -1266,6 +1266,9 @@ void bdrv_format_default_perms(BlockDriverState *b= s, BdrvChild *c, >> bool bdrv_recurse_can_replace(BlockDriverState *bs, >> BlockDriverState *to_replace); >> =20 >> +bool bdrv_is_child_of(BlockDriverState *child, BlockDriverState *parent= , >> + int min_level); >> + >> /* >> * Default implementation for drivers to pass bdrv_co_block_status() t= o >> * their file. >> >=20 >=20 --M3LzYkEBB7aVpGYXfvW2GGHzGhZS6e4kc-- --QGrMx2ztDsGRJL1YnJBsQV7e9AodTSSRi Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl3uXaYACgkQ9AfbAGHV z0BUgQf9F6OTPsaLtr4F4BWForfbGNqoa45MWxz15PrfpP+mBCK851L9LpCx35k/ fj6SKXfQveAOxATbnxzftZSrsxj36HtKnlgYWHXbnOOOThXeBXv1a3CE8hed1+Sk wB/4anlUqRupzOJ9bElvSqJRqWaA1HEJazFyflRGejymMFMHTsqtG5zfjYyob5UN toqHrqsViA0EPiMsEn9nGJOTTk8Zki9gj1L3GtdBaRUPyOZfnQZwPF/bDoU2y4mO 3ojid0TeKnK+RX+mTO1R0g6rDYu5R2nqhDJI7y2PK9QUGVjPtpX5F2MMZg9naIlQ npw0AxhPehab8Sh9lb08YlFyYUKMYA== =UI5z -----END PGP SIGNATURE----- --QGrMx2ztDsGRJL1YnJBsQV7e9AodTSSRi--