[systemd-devel] [PATCH] rules: block - add dm devices to whitelist

[Tomasz Torcz]

On Mon, Jul 10, 2017 at 10:38:38AM +0200, Lennart Poettering wrote:
> On Wed, 05.07.17 13:01, David Disseldorp (ddiss at suse.de) wrote:
> 
> > Ceph relies on by-partuuid symlinks, in order to locate the journal
> > partition from a given OSD partition. For details, see
> > http://tracker.ceph.com/issues/19489.
> 
> This appears way too broad, as it would apply to all LVM and all other
> devices.
> 
> It appears to me Ceph should do the same as LVM does for this, and
> ship its own set of rules, and be careful to only match against the
> actual devices it creates.

 Ceph does not create any devices (except /dev/rbd/* but it's not the case here).
Ceph block storage uses any kind of block device for its operation, be it plain
partition, LUKS encrypted storage, LVM, dm-multipath devices and so on.

  Ceph block storage contains few parts - actual storage, write-ahead log,
journal etc. Any of those parts can utilize block devices, so ceph
uses symlinks to point to proper block device:

# ls -l /var/lib/ceph/osd/ceph-11/block
lrwxrwxrwx. 1 root root 33 Jul 10 10:51 /var/lib/ceph/osd/ceph-11/block -> /dev/disk/by-partuuid/43bdcb85-06


 Nb. ceph already ships rules for autodetecting if given partition belongs
to ceph (discriminating by partition type, see
https://github.com/ceph/ceph/blob/master/udev/95-ceph-osd.rules ), but 'by-partuuid'
links should be created by earlier udev rules - like they are for some whitelisted
set of device nodes names.

-- 
Tomasz Torcz               "Never underestimate the bandwidth of a station
xmpp: zdzichubg at chrome.pl    wagon filled with backup tapes." -- Jim Gray