On Wed 08-01-14 00:31:05, Ted Tso wrote: > The simplest implementation of this design does not require making any > on-disk format changes. We simply suppress the writeback of the dirty > metadata block to the file system. Instead we keep a journal map in > memory, which maps metadata block numbers (or data block numbers if data > journalling is enabled) to a block number in the journal. > > The journal is not truncated when the file system is unmounted, and so > there is no difference between mounting a file system which has been > cleanly unmounted or after a system crash. In both case, the ext4 file > system will scan the journal, and create an in-memory data structure > which maps metadata block locations to their location in the journal. > When a metadata block (or a data block, if data journalling is enabled) > needs to be read, if the block number is found in the journal map, the > block is read from the journal instead of from its "real" location on > disk. So when I was thinking about this (already couple of years ago) the thing which stopped me was the question at which layer we should do the translation. Ideally we would need something at submit_bh() level but just wrapping submit_bh() calls inside ext4 isn't enough for stuff like symlinks or journalled data... Do you have any thoughts on that? Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
