Mailinglist Archive: yast-devel (211 mails)

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Re: [yast-devel] Some notes about new storage API: classes
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, <aschnell@xxxxxxxx>
Senior Software Engineer, Research & Development
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
Maxfeldstraße 5
90409 Nürnberg
Germany
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