[PATCH] Add metadata writing and hot spare processing to hostraid driver in dmraid

[Darrick J. Wong]

Hi all,

Now that dmraid supports Adaptec HostRAID, I've turned my attention to 
enabling support for writing metadata back to the disks, and 
implementing rudimentary spare handling in RAID1 configurations.

The attached patch (which is admittedly very rough) does two key things. 
  First, it implements asr_write in a more meaningful manner than what's 
in rc10 right now; with that part of the patch, dmraid gains the ability 
to reconfigure an array while the system is running and save the changes 
out to disk.  To do this, I had to change a struct to a pointer to a 
struct in asr_reservedblock to to get write_metadata to work properly. 
Also, it turns out that a few more things in asr_write had to happen 
(and in the correct order) for writes to succeed.  If we fail to write 
the metadata correctly, the HostRAID BIOS wipes the entire sector during 
the next reboot.

The second part of the patch stores spare devices in a dummy .asr_spares 
array.  When an I/O error is noticed (via event_io), a suitable spare 
drive is pulled from the spare pool and inserted into the failing array.
I haven't had a chance to test this code rigorously yet, because the 
dmeventd portions of dmraid aren't implemented yet.

So, there are two things that I'd like to see added: online 
reconfiguration support in dmraid (which I can now test via asr_write) 
and online spare handling.  Heinz, are you working on either of these 
features, or should I start writing them?

--D
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