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Fri, 12 Jul 2019 11:05:28 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.208]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4B245600CD; Fri, 12 Jul 2019 11:05:24 +0000 (UTC) To: Kevin Wolf References: <20190711195804.30703-1-mreitz@redhat.com> <20190711195804.30703-4-mreitz@redhat.com> <20190712100439.GD4514@dhcp-200-226.str.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: <9a9b84db-9fed-d3a9-7adc-10220be8123b@redhat.com> Date: Fri, 12 Jul 2019 13:05:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190712100439.GD4514@dhcp-200-226.str.redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Ud8m5AGEnowiNOXGenR0IMFsg31QlcVlq" 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 [10.5.110.41]); Fri, 12 Jul 2019 11:05:28 +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] [RFC 3/5] block: Fall back to fallback truncate function 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: Stefan Hajnoczi , 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) --Ud8m5AGEnowiNOXGenR0IMFsg31QlcVlq Content-Type: multipart/mixed; boundary="OLXP2R3qCifxpFR67s2xIuirHBRlp3E1Y"; protected-headers="v1" From: Max Reitz To: Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Eric Blake , Stefan Hajnoczi Message-ID: <9a9b84db-9fed-d3a9-7adc-10220be8123b@redhat.com> Subject: Re: [RFC 3/5] block: Fall back to fallback truncate function References: <20190711195804.30703-1-mreitz@redhat.com> <20190711195804.30703-4-mreitz@redhat.com> <20190712100439.GD4514@dhcp-200-226.str.redhat.com> In-Reply-To: <20190712100439.GD4514@dhcp-200-226.str.redhat.com> --OLXP2R3qCifxpFR67s2xIuirHBRlp3E1Y Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 12.07.19 12:04, Kevin Wolf wrote: > Am 11.07.2019 um 21:58 hat Max Reitz geschrieben: >> file-posix does not need to basically duplicate our fallback truncate >> implementation; and sheepdog can fall back to it for "shrinking" files= =2E >> >> Signed-off-by: Max Reitz >> --- >> block/file-posix.c | 21 +-------------------- >> block/sheepdog.c | 2 +- >> 2 files changed, 2 insertions(+), 21 deletions(-) >> >> diff --git a/block/file-posix.c b/block/file-posix.c >> index ab05b51a66..bcddfc7fbe 100644 >> --- a/block/file-posix.c >> +++ b/block/file-posix.c >> @@ -2031,23 +2031,7 @@ static int coroutine_fn raw_co_truncate(BlockDr= iverState *bs, int64_t offset, >> return raw_regular_truncate(bs, s->fd, offset, prealloc, errp= ); >> } >=20 > The only thing that is left here is a fstat() check to see that we > really have a regular file here. But since this function is for the > 'file' driver, we can just assume this and the function can go away > altogether. >=20 > In fact, 'file' with block/character devices has been deprecated since > 3.0, so we can just remove support for it now and make it more than jus= t > an assumption. >=20 >> diff --git a/block/sheepdog.c b/block/sheepdog.c >> index 6f402e5d4d..4af4961cb7 100644 >> --- a/block/sheepdog.c >> +++ b/block/sheepdog.c >> @@ -2301,7 +2301,7 @@ static int coroutine_fn sd_co_truncate(BlockDriv= erState *bs, int64_t offset, >> max_vdi_size =3D (UINT64_C(1) << s->inode.block_size_shift) * MAX= _DATA_OBJS; >> if (offset < old_size) { >> error_setg(errp, "shrinking is not supported"); >> - return -EINVAL; >> + return -ENOTSUP; >> } else if (offset > max_vdi_size) { >> error_setg(errp, "too big image size"); >> return -EINVAL; >=20 > The image will be unchanged and the guest will keep seeing the old imag= e > size, so is there any use case where having the fallback here makes > sense? The only expected case where an image is shrunk is that the user= > explicitly sent block_resize - and in that case returning success, but > doing nothing achieves nothing except confusing the user. >=20 > file-posix has the same confusing case, but at least it also has cases > where the fake truncate actually achieves something (such a allowing to= > create images on block devices). Hm, yes, that=E2=80=99s right. It is as confusing for block devices, but= that at least gives something in return. For sheepdog (and others, like ssh), there is nothing in return. Explaining for every block driver why it needs to be a bit confusing and fall back to the fixed-size device implementation (because it doesn=E2=80= =99t implement creation) seems a bit off, too. Hm. Maybe the protocol creation fallback should just ignore failures when truncating an image and in such a case zero the first sector of the image? Maybe it should just ignore ENOTSUP errors? Max --OLXP2R3qCifxpFR67s2xIuirHBRlp3E1Y-- --Ud8m5AGEnowiNOXGenR0IMFsg31QlcVlq Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl0oaXMACgkQ9AfbAGHV z0B0PAgAxA+D6srH1Fdy2C++fs4MJqTB9OfFwTK6DTD8zx9QKsK3oypDz8A6yCl2 ATV+bSNZ3uh5ZlxNEF1QyJElnDFGwtuIqC0n+Yg8ks5eFDGwwszYU0mTT/H5y+2E /ETEJpJblMnHfw3bhQdyQp/V2sNZfJTWjppVCsaTubHwBnYjoCFb3bIX7SAdjlct OgB9LNHl8P+Up5Q6qUNQgVu7owk2Ua1IUQGBAvLoZt97+YlNY/2K0tgyda5j486C 8+k18GNNaCJLg2/oYoAzhaQQR1Cz8XZZpbx8BUy0BzQIITTL13xcLidRYUXzoDS4 rCwJRVqxRpp1m+LtkT9csisUARv4iw== =vZTS -----END PGP SIGNATURE----- --Ud8m5AGEnowiNOXGenR0IMFsg31QlcVlq--