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
