[BUG]
Command `btrfs scrub start -B` and `btrfs scrub status` are reporting
very different results for "Total to scrub":
$ sudo btrfs scrub start -B /mnt/btrfs/
scrub done for c107ef62-0a5d-4fd7-a119-b88f38b8e084
Scrub started: Mon Jun 5 07:54:07 2023
Status: finished
Duration: 0:00:00
Total to scrub: 1.52GiB
Rate: 0.00B/s
Error summary: no errors found
$ sudo btrfs scrub status /mnt/btrfs/
UUID: c107ef62-0a5d-4fd7-a119-b88f38b8e084
Scrub started: Mon Jun 5 07:54:07 2023
Status: finished
Duration: 0:00:00
Total to scrub: 12.00MiB
Rate: 0.00B/s
Error summary: no errors found
This can be very confusing for end users.
[CAUSE]
It's the function print_fs_stat() handling the "Total to scrub" output.
For `btrfs scrub start` command, we use the used bytes (aka, the total
used dev extents of a device) for output.
This is not really accurate, as the chunks may be mostly empty just like
the following:
$ btrfs fi df /mnt/btrfs/
Data, single: total=1.01GiB, used=9.06MiB
System, DUP: total=40.00MiB, used=64.00KiB
Metadata, DUP: total=256.00MiB, used=1.38MiB
GlobalReserve, single: total=22.00MiB, used=0.00B
Thus we're reporting 1.5GiB to scrub (1.01GiB + 40MiB * 2 + 256MiB * 2).
But in reality, we only scrubbed 12MiB
(9.06MiB + 64KiB * 2 + 1.38MiB * 2).
[FIX]
Instead of using the used dev-extent bytes of a device, go with proper
scrubbed bytes for each device.
This involves print_fs_stat() and print_scrub_dev() called inside
scrub_start().
Now the output should match each other.
Issue: #636
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
c88ac0170b