btrfs.mkfs reports incorrect minimum size

[WesleyAC]

If I run mkfs.btrfs on a disk that is less than 41943040 bytes, I get:

ERROR: 'test.img' is too small to make a usable filesystem
ERROR: minimum size for each btrfs device is 41943040

However, the actual minimum size seems to be much higher. Disks of up to 80MB in size report:

ERROR: not enough free space to allocate chunk

It seems like it would be more useful to report the size needed to successfully complete in the first message.

Checked on mkfs.btrfs, part of btrfs-progs v4.12.1.

[adam900710]

Are you using --rootdir option?

In that case, it will need extra space for the content.
The minimal size reported is just to make an empty, mountable fs with some spare space.

[WesleyAC]

No, I wasn't using the --rootdir flag. The command was mkfs.btrfs filesystem.img.

[adam900710]

OK, this is a regression.

v4.0 btrfs-progs is still OK, I assume it's chunk allocator causing the problem.
Bisect under way.

[adam900710]

commit c11e36a
Author: Chandan Rajendra chandan@linux.vnet.ibm.com
Date: Wed Oct 14 23:09:37 2015 +0530

Btrfs-progs: Do not force mixed block group creation unless '-M' option is specified

OK, that's because we're no longer forcing mixed block group for small filesystem.
While the minimal size calculation is still based on mixed block group.

I'll update the minimal size calculator to handle both mixed block group and current separate profiles.

[adam900710]

@WesleyAC
Patch sent. You could help review/ test the patch.
(Sorry, I just sent it to mail list)

https://patchwork.kernel.org/patch/10001161/
https://patchwork.kernel.org/patch/10001159/

[cmurf]

Possible related/dup bug.
https://bugzilla.kernel.org/show_bug.cgi?id=112461

[adam900710]

Will be addressed by pull request #66

[kdave]

The mkfs and minimal size fixes have been merged to devel branch, this was an independent part of the #66 pull.