On 2005-04-10T19:29:31, Lars Marowsky-Bree <lmb@xxxxxxx> wrote: This has generated absolutely no comments, so I'm resending it... > On 2005-02-15T20:17:10, shahid shaikh <shahid.shaikh@xxxxxxxxx> wrote: > > Sorry about this late reply, but I just stumbled across this post. > > To recap, the issue is that we want to prevent LVM2/EVMS2 etc from > scanning (and using!) the raw physical devices if those are already > claimed/used by multipath. > > LVM2 has a special handling for md_component_detection already; what I > want to propose in the following is a bit more general, and I've > discussed it with Hannes before. > > Problem: A general solution for finding out whether another component is > using the device we're looking at. > > Proposed solution: Introduce sub-devices into the sysfs tree. (And, > automatically, backlink those to parent devices, but that's just so the > tree can be traversed in any order.) > > For example, /sys/block/sda would have a sub/ directory with "dm-0" in > there, pointing at /sys/block/dm-0 (surprise). The > /sys/block/dm-0/parent/sd{a,b} entries would do a very surprising > thing. > > This would also allow us to handle partitions in DM better: as all > linear mappings on top of /dev/dm-0 would show up in block/dm-0/sub/ and > vice versa. > > md could work the same: block/sys/md0/parent/ would list all the devices > (or partitions) which it consists of. > > This very simple(?) change would make a number of things much easier to > figure out. > > > Caveats: > > - This obviously only works if the devices are already active, not if > the specific user is offline; if LVM2 scans before multipath-tools has > worked its magic, it won't work. > > (But then, multipath-tools can figure out that there's already someone > else using the raw physical device and not mess with it! Woho, world > saved!) > > - This ONLY exports very rudimentary hierarchical information; it won't > tell you what the device is used for or how. However, that information > alone would be very helpful already. > > > Greg, Alasdair? List? > > Sincerely, Lars Marowsky-Brée <lmb@xxxxxxx> -- High Availability & Clustering SUSE Labs, Research and Development SUSE LINUX Products GmbH - A Novell Business