> On Sun, Jan 24, 2010 at 09:37:07PM +0000, Al Viro wrote: > > On Mon, Jan 25, 2010 at 12:15:51AM +0300, Dmitry Monakhov wrote: > > > > > > It's not a solution. You get an _attempted_ remount ro making writes > > > > fail, even if it's going to be unsuccessful. No go... > > > We have two options for new writers: > > > 1) Fail it via -EROFS > > > Yes, remount may fail, but it is really unlikely. > > > 2) Defer(block) new writers on until we complete or fail remount > > > for example like follows. Do you like second solution ? > > > > Umm... I wonder what the locking implications would be... Frankly, > > I suspect that what we really want is this: > > * per-superblock write count of some kind, bumped when we decide > > that writeback is inevitable and dropped when we are done with it (the > > same thing goes for async part of unlink(), etc.) > > * fs_may_remount_ro() checking that write count > > So basically we try to push those short-term writers to completion and > > if new ones had come while we'd been doing that (or some are really > > stuck) we fail remount with -EBUSY. > > Perhaps we could utilise the filesystem freeze infrastructure - it > already has hooks for intercepting new writers and modifcations, > and filesystems have to flush any current modifications before the freeze > completes. It sounds very similar to the requirements needed here... There are filesystems (e.g. ext2 or UDF) which don't support freezing so it's not an option at least short term... Honza -- Jan Kara <jack@xxxxxxx> SuSE CR Labs -- 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
