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Tue, 20 Aug 2019 12:09:28 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.11]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8835D5D9D5; Tue, 20 Aug 2019 12:09:27 +0000 (UTC) To: Eric Blake , qemu-block@nongnu.org References: <20190819185602.4267-1-mreitz@redhat.com> <20190819185602.4267-13-mreitz@redhat.com> <272cbeba-2053-9aa6-7ceb-e1b3827de540@redhat.com> 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: <39066a69-e319-c3ad-7b3b-2983bb248a25@redhat.com> Date: Tue, 20 Aug 2019 14:09:25 +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: <272cbeba-2053-9aa6-7ceb-e1b3827de540@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="2XdxdbbIMRBjIaxpX0ERdDR1LKrTVsANl" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Tue, 20 Aug 2019 12:09:29 +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] [PATCH v2 12/16] qcow2: Fix overly long snapshot tables 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 , 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) --2XdxdbbIMRBjIaxpX0ERdDR1LKrTVsANl Content-Type: multipart/mixed; boundary="FzlbyzU3oVCjYdHH811GmSykL0eBNsf1Y"; protected-headers="v1" From: Max Reitz To: Eric Blake , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Kevin Wolf Message-ID: <39066a69-e319-c3ad-7b3b-2983bb248a25@redhat.com> Subject: Re: [PATCH v2 12/16] qcow2: Fix overly long snapshot tables References: <20190819185602.4267-1-mreitz@redhat.com> <20190819185602.4267-13-mreitz@redhat.com> <272cbeba-2053-9aa6-7ceb-e1b3827de540@redhat.com> In-Reply-To: <272cbeba-2053-9aa6-7ceb-e1b3827de540@redhat.com> --FzlbyzU3oVCjYdHH811GmSykL0eBNsf1Y Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 19.08.19 21:43, Eric Blake wrote: > On 8/19/19 1:55 PM, Max Reitz wrote: >> We currently refuse to open qcow2 images with overly long snapshot >> tables. This patch makes qemu-img check -r all drop all offending >> entries past what we deem acceptable. >> >> Signed-off-by: Max Reitz >> --- >> block/qcow2-snapshot.c | 88 +++++++++++++++++++++++++++++++++++++----= - >> 1 file changed, 78 insertions(+), 10 deletions(-) >=20 > I know I was reluctant in v1, but you also managed to convince me that > it really takes a LOT of effort to get a table with that many entries. > And a user has to opt-in to 'qemu-img -r' (it may discard a snapshot > they value, but that beats not being able to use the image under qemu a= t > all, and we don't erase it for plain 'qemu-img check'). So I'm okay > with this going in. Maybe the commit message can state this sort of > reasoning. So maybe: The user cannot choose which snapshots are removed. This is fine because we have chosen the maximum snapshot table size to be so large (64 MB) that it cannot be reasonably reached. If the snapshot table exceeds this size, the image has probably been corrupted in some way; in this case, it is most important to just make the image usable such that the user can copy off at least the active layer. (Also note that the snapshots will be removed only with "-r all", so a plain "check" or "check -r leaks" will not delete any data.) ? 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