Hi Ilya, For regular devices such as /dev/vdb2 or /dev/sda3, do you think it is safe to use /sys/dev/block/M:m/partition to figure out the partition number ? Or could it vary depending on the disk driver or the partition table layout ? Or the kernel version ? Cheers On 16/08/2015 00:10, Loic Dachary wrote: > > > On 16/08/2015 00:00, Ilya Dryomov wrote: >> On Sat, Aug 15, 2015 at 11:56 PM, Loic Dachary <loic@xxxxxxxxxxx> wrote: >>> Hi Ilya, >>> >>> On 15/08/2015 19:42, Ilya Dryomov wrote: >>>> On Sat, Aug 15, 2015 at 6:35 PM, Loic Dachary <loic@xxxxxxxxxxx> wrote: >>>>> 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 /dev/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 hack. >>>>>>> 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 necessarily >>>>>>> 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 up with. >>>>>> Basically it checks if the device name appears as /sys/block/*/$foo... >>>> >>>> For regular devices, you can access() /sys/dev/block/maj:min/partition. >>>> 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 instead 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 should >>>> 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 is >>>> 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 asking dmsetup with: >> >> Yes, I think so. I'm pretty sure these "part<id>-" and "mpath-" >> prefixes were devised for exactly this purpose. >> > > Excellent ! > >> Thanks, >> >> Ilya >> > -- Loïc Dachary, Artisan Logiciel Libre
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