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Wed, 19 Aug 2020 15:35:24 +0000 (UTC) Subject: Re: [PATCH v7 10/47] mirror-top: Support compressed writes To: Kevin Wolf References: <20200625152215.941773-1-mreitz@redhat.com> <20200625152215.941773-11-mreitz@redhat.com> <20200818102734.GC6865@linux.fritz.box> 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: Wed, 19 Aug 2020 17:35:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200818102734.GC6865@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ZC0pcH0s56SGNIalODk46d1NfZ2hmGFdc" Received-SPF: pass client-ip=207.211.31.81; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/19 01:46:53 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, qemu-block@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) --ZC0pcH0s56SGNIalODk46d1NfZ2hmGFdc Content-Type: multipart/mixed; boundary="coZsQ656yyszpRryIBAFY7gAWukPabRS7" --coZsQ656yyszpRryIBAFY7gAWukPabRS7 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 18.08.20 12:27, Kevin Wolf wrote: > Am 25.06.2020 um 17:21 hat Max Reitz geschrieben: >> Signed-off-by: Max Reitz >> --- >> block/mirror.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/block/mirror.c b/block/mirror.c >> index e8e8844afc..469acf4600 100644 >> --- a/block/mirror.c >> +++ b/block/mirror.c >> @@ -1480,6 +1480,15 @@ static int coroutine_fn bdrv_mirror_top_pdiscard(= BlockDriverState *bs, >> NULL, 0); >> } >> =20 >> +static int coroutine_fn bdrv_mirror_top_pwritev_compressed(BlockDriverS= tate *bs, >> + uint64_t off= set, >> + uint64_t byt= es, >> + QEMUIOVector= *qiov) >> +{ >> + return bdrv_mirror_top_pwritev(bs, offset, bytes, qiov, >> + BDRV_REQ_WRITE_COMPRESSED); >> +} >=20 > Hm, not sure if it's a problem, but bdrv_supports_compressed_writes() > will now return true for mirror-top. However, with an active mirror to a > target that doesn't support compression, trying to actually do a > compressed write will always return -ENOTSUP. Right. > So I guess the set of nodes patch 7 looks at still isn't quite complete. > However, it's not obvious how to make it more complete without > delegating to the driver. >=20 > Maybe we need to use bs->supported_write_flags, which is set by the > driver, instead of looking at the presence of callbacks. Hm, yes, that would work better. Not sure if it=E2=80=99s worth it for thi= s series. The only problem we=E2=80=99d have is late failure when trying to do a compressed backup to a target that=E2=80=99s running an active mirror. (La= te as in =E2=80=9Cfirst write fails without explanation=E2=80=9D, as opposed to = =E2=80=9Cjob fails during set-up=E2=80=9D.) Which I hope is not a case anyone would ever encounter, and even if they do, the failure doesn=E2=80=99t seem catastrophic to me. So I don=E2=80=99= t think it=E2=80=99s really a problem. Max --coZsQ656yyszpRryIBAFY7gAWukPabRS7-- --ZC0pcH0s56SGNIalODk46d1NfZ2hmGFdc Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl89RroACgkQ9AfbAGHV z0AHNAf/UTOanDwtcV7tT7dUW4n010mYnUX9QuwIOnuGSGU8rn2ckViDzLd6ANuN W/M8hiLdzDK4VX1PLAE5X2DQDc36DP3Ecd1tS3ZUHRUBb/sFY68/h2y8ioDD5O0a 9cPQJU6v3S3exrQlDWrCqZfribvYCvhlodKYEyeHX+WaLi4foh7pGHWjoTY5TF2C PugJP5Cn11N5lA/LWuvytl4SXxuZnsZEqQ/v9/k9sUc95XIt76sxhIH07kSuX72B vCOPI/qQjKIjPZs75OqxOFgV3FKyfxE5ln2Nzz05pGJyb6a5rE/5cTRT0eniBAjO Sc4hvmR0pb7DbgW4S4HwGpmRevJ0PA== =l/jC -----END PGP SIGNATURE----- --ZC0pcH0s56SGNIalODk46d1NfZ2hmGFdc--