Hi Tytso, I tried to do some power failure tests, but I was unable to simulate an error, as you described. I analysed code by myself, but I don't see any problem with starting a new transaction in function ext4_ext_rm_leaf. If in this function new transaction is created and system will crash in the middle of deleting the file, eh_entries in extent_header will have correct value, so it shouldn't cause any problem (eh_entries is decremented in the same transaction, as zeroing out ex->len etc.). I hope, you will understand, what I want to say. If I'm wrong, please let me know. Regards, Lubos tytso@xxxxxxx píše v Út 18. 03. 2014 v 13:14 -0400: > On Tue, Mar 18, 2014 at 04:09:30PM +0100, Lubos Uhliarik wrote: > > The main changes in patch are following: > > > > a) commented out zeroing ex->ee_len, ee->start_hi and ee->start_lo, > > because these entries are essential for undelete process > > The reason why we have to zero out ex->ee_len, etc. is because the > truncate operation can sometimes span multiple journal transactions. > So as a result, we need to keep the file system consistent if we are > interrupted (i.e., via a power fail event) while in the middle of a > truncate operation. > > It's a rare case, but it can happen if the journal is almost full at > the time when the truncate eoperation has started, such that there is > no room for to exntend the transaction handle, and so we are forced to > start a new transaction (and possibly wait for a journal checkpoint > operation). > > In theory, it would be possible to figure out in advance whether or > not we could fit the truncate in a single transaction, but it would > require making the truncate operation be a two-pass operation --- once > to determine how many blocks needs to be modified, and once to > actually do the truncate operation. > > > This patch shouldn't break ext4, I tested it with xfs_tests and tests > > were successfull. > > I'm guessing you didn't do power fail testing --- and this is very > important when messing with the design truncate/unlink code path. > > Regards, > > - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
