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requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C6D5C19067E0; Tue, 28 Jul 2020 14:10:08 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-112-145.ams2.redhat.com [10.36.112.145]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 842AD73023; Tue, 28 Jul 2020 14:10:07 +0000 (UTC) Subject: Re: [PATCH v7 41/47] block: Leave BDS.backing_file constant To: Andrey Shinkevich , qemu-block@nongnu.org References: <20200625152215.941773-1-mreitz@redhat.com> <20200625152215.941773-42-mreitz@redhat.com> <17ef88da-15fc-57ae-801e-a5374e87743f@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 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Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 27.07.20 14:27, Andrey Shinkevich wrote: > On 25.06.2020 18:22, Max Reitz wrote: >> Parts of the block layer treat BDS.backing_file as if it were whatever >> the image header says (i.e., if it is a relative path, it is relative to >> the overlay), other parts treat it like a cache for >> bs->backing->bs->filename (relative paths are relative to the CWD). >> Considering bs->backing->bs->filename exists, let us make it mean the >> former. >> >> Among other things, this now allows the user to specify a base when >> using qemu-img to commit an image file in a directory that is not the >> CWD (assuming, everything uses relative filenames). >> >> Before this patch: >> >> $ ./qemu-img create -f qcow2 foo/bot.qcow2 1M >> $ ./qemu-img create -f qcow2 -b bot.qcow2 foo/mid.qcow2 >> $ ./qemu-img create -f qcow2 -b mid.qcow2 foo/top.qcow2 >> $ ./qemu-img commit -b mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find 'mid.qcow2' in the backing chain of >> 'foo/top.qcow2' >> $ ./qemu-img commit -b foo/mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find 'foo/mid.qcow2' in the backing chain of >> 'foo/top.qcow2' >> $ ./qemu-img commit -b $PWD/foo/mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find '[...]/foo/mid.qcow2' in the backing chain of >> 'foo/top.qcow2' >> >> After this patch: >> >> $ ./qemu-img commit -b mid.qcow2 foo/top.qcow2 >> Image committed. >> $ ./qemu-img commit -b foo/mid.qcow2 foo/top.qcow2 >> qemu-img: Did not find 'foo/mid.qcow2' in the backing chain of >> 'foo/top.qcow2' >> $ ./qemu-img commit -b $PWD/foo/mid.qcow2 foo/top.qcow2 >> Image committed. >> >> With this change, bdrv_find_backing_image() must look at whether the >> user has overridden a BDS's backing file.=C2=A0 If so, it can no longer = use >> bs->backing_file, but must instead compare the given filename against >> the backing node's filename directly. >> >> Note that this changes the QAPI output for a node's backing_file.=C2=A0 = We >> had very inconsistent output there (sometimes what the image header >> said, sometimes the actual filename of the backing image).=C2=A0 This >> inconsistent output was effectively useless, so we have to decide one >> way or the other.=C2=A0 Considering that bs->backing_file usually at run= time >> contained the path to the image relative to qemu's CWD (or absolute), >> this patch changes QAPI's backing_file to always report the >> bs->backing->bs->filename from now on.=C2=A0 If you want to receive the = image >> header information, you have to refer to full-backing-filename. >> >> This necessitates a change to iotest 228.=C2=A0 The interesting informat= ion >> it really wanted is the image header, and it can get that now, but it >> has to use full-backing-filename instead of backing_file.=C2=A0 Because = of >> this patch's changes to bs->backing_file's behavior, we also need some >> reference output changes. >> >> Along with the changes to bs->backing_file, stop updating >> BDS.backing_format in bdrv_backing_attach() as well.=C2=A0 In order not = to >> change our externally visible behavior (incompatibly), we have to let >> bdrv_query_image_info() try to get the image format from bs->backing if >> bs->backing_format is unset.=C2=A0 (The QAPI schema describes >> backing-filename-format as "the format of the backing file", so it is >> not necessarily what the image header says, but just the format of the >> file referenced by backing-filename (if known).) >> >> iotest 245 changes in behavior: With the backing node no longer >> overriding the parent node's backing_file string, you can now omit the >> @backing option when reopening a node with neither a default nor a >> current backing file even if it used to have a backing node at some >> point. >> >> Signed-off-by: Max Reitz >> --- >> =C2=A0 include/block/block_int.h=C2=A0 | 21 ++++++++++++++++----- >> =C2=A0 block.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 35 ++++++++++++= +++++++++++++++-------- >> =C2=A0 block/qapi.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 17 +++++++++++++---- >> =C2=A0 tests/qemu-iotests/228=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 6 +++--- >> =C2=A0 tests/qemu-iotests/228.out |=C2=A0 6 +++--- >> =C2=A0 tests/qemu-iotests/245=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 4 +++- >> =C2=A0 6 files changed, 65 insertions(+), 24 deletions(-) >> > ... >> diff --git a/block/qapi.c b/block/qapi.c >> index 2628323b63..5da6d7e6e0 100644 >> --- a/block/qapi.c >> +++ b/block/qapi.c >> @@ -47,7 +47,7 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend >> *blk, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0 Error **errp) >> =C2=A0 { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ImageInfo **p_image_info; >> -=C2=A0=C2=A0=C2=A0 BlockDriverState *bs0; >> +=C2=A0=C2=A0=C2=A0 BlockDriverState *bs0, *backing; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BlockDeviceInfo *info; >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!bs->drv) { >> @@ -76,9 +76,10 @@ BlockDeviceInfo >> *bdrv_block_device_info(BlockBackend *blk, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info->node_name = =3D g_strdup(bs->node_name); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 -=C2=A0=C2=A0=C2=A0 if (bs->backing_file[0]) { >> +=C2=A0=C2=A0=C2=A0 backing =3D bdrv_cow_bs(bs); >> +=C2=A0=C2=A0=C2=A0 if (backing) { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info->has_backing= _file =3D true; >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info->backing_file =3D g_str= dup(bs->backing_file); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info->backing_file =3D g_str= dup(backing->filename); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!QLIST_EMPTY(&bs->dirty_bitmap= s)) { >> @@ -314,6 +315,8 @@ void bdrv_query_image_info(BlockDriverState *bs, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 backing_filename =3D bs->backing_file; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (backing_filename[0] !=3D '\0') { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 char *backing_fil= ename2; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const char *backing_format = =3D NULL; >> + >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info->backing_fil= ename =3D g_strdup(backing_filename); >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info->has_backing= _filename =3D true; >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 backing_filename2= =3D bdrv_get_full_backing_filename(bs, NULL); >> @@ -326,7 +329,13 @@ void bdrv_query_image_info(BlockDriverState *bs, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >> =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bs->ba= cking_format[0]) { >> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 info= ->backing_filename_format =3D >> g_strdup(bs->backing_format); >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 back= ing_format =3D bs->backing_format; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } else if (bs->backing && bs= ->backing->bs->drv && >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 !bdrv_backing_overridden(bs)) { >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 back= ing_format =3D bs->backing->bs->drv->format_name; >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >=20 >=20 > In case bdrv_backing_overridden() returns true , should we invoke > bdrv_refresh_filename() and assign the format_name then? I don=E2=80=99t think so. The format we return in info->backing_filename_f= ormat should be the format of the file returned in info->backing_filename. The latter is bs->backing_file, which (as of this patch), is the backing file as reported by the image header. Therefore, if the backing file was overridden, we cannot assume that bs->backing->bs refers to the same file as bs->backing_file, and so we cannot assume bs->backing->bs->drv->format_name to be info->backing_filename=E2=80=99s fo= rmat. Max --ILtv09RkOz8qvWazmUPTBVauMTVaLxloh-- --LeFPUrHmVCPpXx3ACIBaHXyVWhTfScNCT Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl8gMb0ACgkQ9AfbAGHV z0B0fAgAkDgfKtWlJ2kH2ZFRfgEPgend+gnHiGw79+JfnbIFyz7YmatDBOqgKJLI 7/o3K1KURJ4CUTH3SQH5xgZcgaDK4HFyipjxzJB0CnkuhXNH3TPcfaM2wXIwwXV8 KdTSPiGpm712WRxYJHbUUccHCxAYsT5hEVxvYJ+n1dHnKM5UmlfrMjX76o1VQckn KocrQVDW9DfGBSjBMKvRztkoPDE0hw9R6AotVGR6Z0deSEnjC6/vHv72E682+jk8 qOMs6T2ha7GHhXTuqNbN6LWUGAfGqENE46zDg7vqNclp+dwhdnrsOZIHDG+vOgQs 88CXYifsK2Ku8ib9P2q1CJpJ74PDcQ== =iqn4 -----END PGP SIGNATURE----- --LeFPUrHmVCPpXx3ACIBaHXyVWhTfScNCT--