[PATCH V2] Add support for BTRFS raid5/6 to GRUB

[Goffredo Baroncelli]

Hi All,

the aim of this patches set is to provide support for a BTRFS raid5/6
 filesystem in GRUB.

The first patch, implements the basic support for raid5/6. I.e this works when
 all the disks
are present.

The next 4 patches, are preparatory ones.

The last two implements the support for raid5/6 recovery. It allow to read
from the filesystem even when 1 or 2 (for raid 6) disk(s) are missing.

The last one is the more controversial. The code for the raid6 recovery is
copied from the GRUB file reaid6_recovery.c . I preferred this approach,
because the original code assumes that the read is GRUB_DISK_SECTOR_SIZE
bytes based (512 bytes). Instead the GRUB BTRFS implementation need to
read the disk with a granularity of the byte.
I tried to update the code (and the function which the code calls), but
the change was quite invasive. So for now I preferred to duplicating the
code, to get some feedback.

I tested the code in grub-emu, and it works (for me) both with all the disks,
 and with some disks missing. I checked the sh1sums calculated from grub and
from linux and these matched.

Comments are welcome.

BR
G.Baroncelli


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