On 10/1/14 5:43 PM, Theodore Ts'o wrote: > On Wed, Oct 01, 2014 at 03:37:17PM -0500, Eric Sandeen wrote: >> >> Ok. I guess this is only an issue for ext4 - well, at least this specific >> issue. Delalloc makes it much different than ext2 & ext3, which reserve quite a >> lot more. Whether there's a corner case over there which breaks, I dunno... >> >> So it seems like the simplest test is simply: Are we RW mounted with delalloc? >> And if so, update the feature. Seems simpler than mucking with "which features >> are unique to ext4" > > I'd do "are we RW mounted with the extents feature". That way we > don't need to worry about someone accidentally mounting a partition > meant for Hurd using ext4, which would imply delalloc, and then > causing Hurd to no longer be able to deal with the file system. That > *shouldn't* happen, but if someone accidentally mounts the file system > with -t ext4, but it seems safer to gate it on the existence of the > extents feature. Problem is, we can hit the same problem with an ext3 filesystem (no extents) mounted with -t ext4 (enabling delalloc). Ugh. Can't we just bump the da write reservation to 2 and be done with it? ;) (AFAICT the non-delalloc reservations can be wildly overestimated). Or maybe ext4_journal_extend() when we try to update the superblock? It could fail, but it wouldn't be catastrophic if it did, fsck would find that the feature is missing... -Eric -- 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
