On 10/07/2011 11:35 AM, Darrick J. Wong wrote:
Um.... I don't think ext4 should be accessing journal internals. At a bare minimum the stuff that mucks around with jbd2 ought to be in fs/jbd2 and the ext4 parts stuffed in a wrapper in ext4_jbd2.[ch], since ocfs2 also uses jbd2.
I agree.
I'm also wondering -- this logical<-> journal block mapping doesn't seem to be committed to disk anywhere. What happens if jbd2 crashes before we get to zeroing journal blocks? Specifically, would the journal recovery code know that a given journal block also needs secure deletion? Here's a counterproposal: What if ext4 told jbd2 which blocks need to be securely deleted while ext4 is creating the transactions? jbd2 could then set a JBD2_FLAG_SECURE_DELETE flag in journal_block_tag_t.t_flags (the descriptor block), which would tell the recovery and commit code that the associated journal block needs secure deletion when processing is complete. I _think_ you could just extend the functions called by ext4_jbd2.c to take a flags parameter. Does this sound better? Or even sane? :) (Not sure if ocfs2 cares about secure delete at all.)
It looks like a useful feature. Though I would be wary of wiring this in the journaling layer. Mainly for performance reasons. In ocfs2, we log the truncated bits to a node specific system file called truncate_log. These bits are flushed to the global bitmap periodically by a queued task. We do this because taking a cluster lock on the global bitmap is very expensive. If I were doing this, I would extend this scheme to handle secure deletes. The queued task would zero out the clusters before clearing the bits in the global bitmap. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
