[BUG]
For a degraded RAID5, btrfs check will fail to even read the chunk root:
# mkfs.btrfs -f -m raid5 -d raid5 $dev1 $dev2 $dev3
# wipefs -fa $dev1
# btrfs check $dev2
Opening filesystem to check...
warning, device 1 is missing
bad tree block 22036480, bytenr mismatch, want=22036480, have=0
ERROR: cannot read chunk root
ERROR: cannot open file system
[CAUSE]
Although read_tree_block() function from btrfs-progs is properly
iterating the mirrors (mirror 1 is reading from the disk directly,
mirror 2 will be rebuild from parity), the raid56 recovery path is not
handling the read error correctly.
The existing code will try to read the full stripe, but any read failure
(including missing device) will immediately cause an error:
for (i = 0; i < num_stripes; i++) {
ret = btrfs_pread(multi->stripes[i].dev->fd, pointers[i],
BTRFS_STRIPE_LEN, multi->stripes[i].physical,
fs_info->zoned);
if (ret < BTRFS_STRIPE_LEN) {
ret = -EIO;
goto out;
}
}
[FIX]
To make failed_a/failed_b calculation much easier, and properly handle
too many missing devices, here this patch will introduce a new bitmap
based solution.
The new @failed_stripe_bitmap will represent all the failed stripes.
So the initial read will mark all the missing devices in the
@failed_stripe_bitmap, and later operations will all operate on that
bitmap.
Only before we call raid56_recov(), we convert the bitmap to the old
failed_a/failed_b interface and continue.
Now btrfs check can handle above case properly:
# btrfs check $dev2
Opening filesystem to check...
warning, device 1 is missing
Checking filesystem on /dev/test/scratch2
UUID: 8b2e1cb4-f35b-4856-9b11-262d39d8458b
[1/7] checking root items
[2/7] checking extents
[3/7] checking free space tree
[4/7] checking fs roots
[5/7] checking only csums items (without verifying data)
[6/7] checking root refs
[7/7] checking quota groups skipped (not enabled on this FS)
found 147456 bytes used, no error found
total csum bytes: 0
total tree bytes: 147456
total fs tree bytes: 32768
total extent tree bytes: 16384
btree space waste bytes: 139871
file data blocks allocated: 0
referenced 0
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
