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Thu, 13 Jun 2019 14:19:40 +0000 (UTC) To: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" References: <20190612221004.2317-1-mreitz@redhat.com> <20190612221004.2317-12-mreitz@redhat.com> <7a0fe60a-0d16-5420-0c6a-65cfe01bc933@virtuozzo.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: <187cae6d-c9f1-7adb-aca9-5d0ba977de43@redhat.com> Date: Thu, 13 Jun 2019 16:19:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <7a0fe60a-0d16-5420-0c6a-65cfe01bc933@virtuozzo.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="6vcGHSR6dj1chBEr0lp1MOYpIYATotnBx" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Thu, 13 Jun 2019 14:19:42 +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 v5 11/42] block: Add bdrv_supports_compressed_writes() 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) --6vcGHSR6dj1chBEr0lp1MOYpIYATotnBx Content-Type: multipart/mixed; boundary="2qFuF8NjhXuyUUZY4x3xIlgjJzSR7qwzl"; protected-headers="v1" From: Max Reitz To: Vladimir Sementsov-Ogievskiy , "qemu-block@nongnu.org" Cc: "qemu-devel@nongnu.org" , Kevin Wolf Message-ID: <187cae6d-c9f1-7adb-aca9-5d0ba977de43@redhat.com> Subject: Re: [PATCH v5 11/42] block: Add bdrv_supports_compressed_writes() References: <20190612221004.2317-1-mreitz@redhat.com> <20190612221004.2317-12-mreitz@redhat.com> <7a0fe60a-0d16-5420-0c6a-65cfe01bc933@virtuozzo.com> In-Reply-To: <7a0fe60a-0d16-5420-0c6a-65cfe01bc933@virtuozzo.com> --2qFuF8NjhXuyUUZY4x3xIlgjJzSR7qwzl Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 13.06.19 15:29, Vladimir Sementsov-Ogievskiy wrote: > 13.06.2019 1:09, Max Reitz wrote: >> Filters cannot compress data themselves but they have to implement >> .bdrv_co_pwritev_compressed() still (or they cannot forward compressed= >> writes). Therefore, checking whether >> bs->drv->bdrv_co_pwritev_compressed is non-NULL is not sufficient to >> know whether the node can actually handle compressed writes. This >> function looks down the filter chain to see whether there is a >> non-filter that can actually convert the compressed writes into >> compressed data (and thus normal writes). >=20 > Why not to use this function in (as I remember only 2-3 cases) when > we check for bs->drv->bdrv_co_pwritev_compressed? It would be a complet= e fix > for described problem. Well, bdrv_driver_pwritev_compressed() doesn=E2=80=99t really care, it wi= ll find out sooner or later anyway (while being passed down the chain). This is only really important for the backup job, which will use this function as of patch 26. (It isn=E2=80=99t important before 26, because using fil= ters with backup generally is a gamble before that patch.) > (hmm, ok, other new APIs are added separately too, for some reason they= don't > confuse me and this confuses) >=20 > On the other hand, (the second time I think about it during review), co= uld > we handle compression through flags completely? > We have supported_write_flags feature, which should be used for all the= se checks.. > And may be, we may drop .bdrv_co_pwritev_compressed at all. We probably could, yes. I just felt like this wasn=E2=80=99t the time to= do it. O:-) > But if you want to keep it as is, it's OK too: > Reviewed-by: Vladimir Sementsov-Ogievskiy Thanks for reviewing! Max --2qFuF8NjhXuyUUZY4x3xIlgjJzSR7qwzl-- --6vcGHSR6dj1chBEr0lp1MOYpIYATotnBx Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl0CW3sACgkQ9AfbAGHV z0CdAQf/d3CneSCTEjpC2G1vgsc8TCbejhSWKnbjjbEU5KF8wxesDKoj0xDbXA7Z d4CruHK4bbiMovDNLnQGJmxvRZhG9aOUJuvR6QmAGb+0b8Yu+OzgaFW0JxOyWerQ sgyEWtGCegsbvznNtCP79rvSNQ8TbMRl3F8gMH9Hz4dCd8XjdxzExLPNKZrsG210 haJw53YGbLAmn+7IAC1s7h38g0Gv5mxN5WVs/3Y1ep9U+ondYJYckGa1JUWkVZUT Tm3o0OcUbsY5YE2Ukm07ZtZtfnuqNZd5NF5rfRt8rDauWFt+0O4ykt6OFcAsHQXL go/Ofto4wi2IqHRthkkIXi70fef25g== =8gWQ -----END PGP SIGNATURE----- --6vcGHSR6dj1chBEr0lp1MOYpIYATotnBx--