Add raid level takeover support allowing arbitrary takeovers between
raid levels supported by md personalities (i.e. raid0, raid1/10 and
raid4/5/6):
- add rs_config_{backup|restore} function to allow for temporary
storing ctr requested layout changes and restore them for takeover
conersion decision after the superblocks got loaded and analyzed
- add members to store layout to 'struct raid_set' (not mandatory
for takeover but needed for reshape in later patch)
- add rebuild_disks bitfield to 'struct raid_set' and set bits in ctr
to use in setting up takeover (base to address a 'rebuild' related
raid_status() table line bug and needed as well for reshape in future
patch)
- add runtime flags and respective manipulation functions to be able to
control e.g. wrting of superlocks to the preresume function on
takeover and (later) reshape
- add functions to detect takeover, check it's valid (mandatory here to
avoid failing on md_run()), setup for it and use in the ctr; those
will be likely moved out once reshaping gets added to simplify the
ctr
- start raid set readonly in ctr and switch to readwrite, optionally
updating superblocks, in preresume in order to allow suspend to
quiesce any active table before (which involves superblock updates);
this ensures the proper sequence of writing the current and any new
takeover(/reshape) metadata
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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