From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Dachary Subject: Re: /sys/block and /dev and partitions Date: Sun, 16 Aug 2015 00:10:22 +0200 Message-ID: <55CFB8CE.10508@dachary.org> References: <55CF1F99.5050807@dachary.org> <55CF5C4B.2010406@dachary.org> <55CFA778.6030703@dachary.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="It4gP2dxqjproxFtrEhPkw8LhAXJR9E6g" Return-path: Received: from mail2.dachary.org ([91.121.57.175]:38670 "EHLO smtp.dmail.dachary.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751103AbbHOWK0 (ORCPT ); Sat, 15 Aug 2015 18:10:26 -0400 In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Ilya Dryomov Cc: Ceph Development This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --It4gP2dxqjproxFtrEhPkw8LhAXJR9E6g Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 16/08/2015 00:00, Ilya Dryomov wrote: > On Sat, Aug 15, 2015 at 11:56 PM, Loic Dachary wrote= : >> Hi Ilya, >> >> On 15/08/2015 19:42, Ilya Dryomov wrote: >>> On Sat, Aug 15, 2015 at 6:35 PM, Loic Dachary wrot= e: >>>> Hi Sage, >>>> >>>> On 15/08/2015 16:28, Sage Weil wrote: >>>>> On Sat, 15 Aug 2015, Loic Dachary wrote: >>>>>> Hi, >>>>>> >>>>>> Is there a portable and consistent way to figure out if a given /d= ev/XXX >>>>>> path (for instance /dev/dm-1) is a partition of a whole device ? >>>>>> Although checking /sys/block/dm-1/dm/name for a number at the end = (like >>>>>> mpatha1 or mpatha2) would probably work, it feels like a fragile h= ack. >>>>>> Looking into /sys/block/dm-1/slaves will lead to >>>>>> /sys/block/dm-1/slaves/dm-0 and we can check that >>>>>> /sys/block/dm-*/subsystem is class/block. But that does not necess= arily >>>>>> mean dm-1 is a partition of dm-0, just that it's a slave of dm-0. >>>>> >>>>> Take a look at is_partition in ceph-disk, whih is the best I came u= p with. >>>>> Basically it checks if the device name appears as /sys/block/*/$foo= =2E.. >>> >>> For regular devices, you can access() /sys/dev/block/maj:min/partitio= n. >>> If it's there, it's a partition - no need to iterate over /sys/block.= >> >> I added http://tracker.ceph.com/issues/12706 for when someone has time= to rework that part of the code. >> >>> >>>> >>>> That is consistently updated for /dev/sdb or /dev/vdb but things are= different when using multipath. I'll rely on /sys/block/dm-?/dm/name ins= tead until a better solution is found. >>> >>> A better way might be to rely on the fact that a dm partition will >>> necessarily have its uuid prefixed by "part". In that case, it shoul= d >>> be safe to assume that the thing in slaves is a whole disk - I think >>> that's what various util-linux tools do. However, IIRC the dm uuid i= s >>> optional, so that won't work on a dm device without a uuid. >> >> It looks like multipath on both CentOS 7 and Ubuntu 14.04 set the uuid= in this way. >> >> Is it also safe to assume that if the uuid is: >> >> $ cat /sys/dev/block/253:?/dm/uuid >> mpath-353333330000007d0 >> part1-mpath-353333330000007d0 >> part2-mpath-353333330000007d0 >> >> it means these were created by multipath because of the mpath ? When a= sking dmsetup with: >=20 > Yes, I think so. I'm pretty sure these "part-" and "mpath-" > prefixes were devised for exactly this purpose. >=20 Excellent ! > Thanks, >=20 > Ilya >=20 --=20 Lo=C3=AFc Dachary, Artisan Logiciel Libre --It4gP2dxqjproxFtrEhPkw8LhAXJR9E6g Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iEYEARECAAYFAlXPuM4ACgkQ8dLMyEl6F20EKQCfed683EVgBNZQ+RVcHPi4eigk aUEAn21cvAcfNmxMnPisVouw83iVmvMi =9aSW -----END PGP SIGNATURE----- --It4gP2dxqjproxFtrEhPkw8LhAXJR9E6g--