On Thu, Oct 15, 2015 at 06:17:06PM +0200, Arvin Schnell wrote: > On Thu, Oct 15, 2015 at 05:30:15PM +0200, Martin Vidner wrote:
> > What is a Holder? It seems to be characterized by having a source > > sid and a target sid, which still does not give me a hint. > > Its subclasses Subdevice and User are even more opaque to me. > > Technical it's the edge in the graph, so it expresses what device > is linked what device. The name I have borrowed from sysfs (but > it's not the same as in sysfs), e.g. on my system I have > (simplified) > > # ll /sys/block/sda/sda2/holders/ > lrwxrwxrwx 1 root root 0 Oct 15 17:17 dm-0 -> > ../../../../../../../../../../virtual/block/dm-0 > lrwxrwxrwx 1 root root 0 Oct 15 17:17 dm-1 -> > ../../../../../../../../../../virtual/block/dm-1 > > In the graph there are different holders. > > - Subdevice: E.g. a partition is the subdevice of a Disk and a > logical volume is the subdevice of a volume group. > > - User: E.g. a partition is used by a volume group (the case on > my system), a disk is used by a RAID, a logical volume is used > by a filesystem. > > So far the distinction is not really important so it could > change. The idea is of course to have more Holder classes that even have data. E.g. a RaidUser which has a "spare device" flag or a FilesystemUser which has a "journal/log device" flag. By keeping that data in the holders you don't need special care when manipulating the graph, e.g. removing a device or copying the graph. With extra lists in the Raid or Filesystem object such special care would be needed. ciao Arvin -- Arvin Schnell, <[email protected]> Senior Software Engineer, Research & Development SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) Maxfeldstraße 5 90409 Nürnberg Germany -- To unsubscribe, e-mail: [email protected] To contact the owner, e-mail: [email protected]
