Re: [Help] Errors found in extent allocation tree or chunk allocation

[Michael Witten <mfwitten@gmail.com>]

On Tue, 1 Apr 2014 07:15:47 +0800, Shilong Wang wrote:

> hello, recently, i was working on btrfsck repair. i post some
> patches to make btrfsck to rebuild extent tree with snapshots.
> you can pull code from david latest branch and have a try with
> btrfsck --init-extent-tree.

Fortunately, the `btrfs balance' command solved the issue for me:

  http://mid.gmane.org/<8e4932bb29f743419660da1846c2363b-mfwitten@gmail.com>

However, I did notice `--init-extent-tree' when trying to figure
out what I might do to fix my troubles; however, I was uncertain
about exactly what it would do.

According to `man btrfsck':

  --init-csum-tree
       create a new CRC tree.

  --init-extent-tree
       create a new extent tree.

These sound potentially destructive, so I was afraid to use them;
what exactly does it mean to create a new tree? After your email,
I assume each action creates a new tree that is populated from the
data in the corresponding old tree.

Also, you wrote:

> rebuild extent tree with snapshots

Do you mean to say that your patches handle the previously unhandled
case in which both of the following are true?

  * There are snapshots in the file system.
  * The extent tree needs to be rebuilt.

Thanks!