[LU-433] remove jbd2-jcberr patch from kernel

Related — Wed, 3 Dec 2014 19:33:46 +0000

In the upstream ext4 code there is a new functionality to allow a per-commit callback to be set
(j_commit_callback), which is used by the mballoc code to manage free space bitmaps after deleted
blocks have been released. It should be fairly straight forward to allow the j_commit_callback and
t_private_list to be multiplexed, by creating a new ext4_commit_callback() function that just walks
a list of function+data pointers attached to t_private_list, much like the jbd2-jcberr code
currently walks the callback list, and passes is_journal_aborted() as the callback error parameter.

A new ext4_journal_callback_set() function, using the same API as the existing
jbd2_journal_callback_set(), will maintain a list of function+data pointers on t_private_list, and
the current code that manipulates t_private_list directly would now call
ext4_journal_callback_set() with a modified release_blocks_on_commit() as the callback function
(taking a pointer to struct ext4_delete_entry as data, and only freeing one structure at a time).

Within the existing code, ext4_mb_free_metadata() is manually removing existing entries from the
callback list if they can be merged. This functionality doesn't currently exist, but it shouldn't
be hard to add an ext4_journal_callback_del() function to remove the entry from the list, if passed
the journal_callback struct, which would now be embedded into struct ext4_delete_entry instead of
just the list_head "list".

Whamcloud Community JIRA

[LU-433] remove jbd2-jcberr patch from kernel