On Mon, 2022-09-12 at 15:20 +0200, Florian Weimer wrote: > * Jeff Layton: > > > On Mon, 2022-09-12 at 14:13 +0200, Florian Weimer wrote: > > > * Jeff Layton: > > > > > > > To do this we'd need 2 64-bit fields in the on-disk and in-memory > > > > superblocks for ext4, xfs and btrfs. On the first mount after a crash, > > > > the filesystem would need to bump s_version_max by the significant > > > > increment (2^40 bits or whatever). On a "clean" mount, it wouldn't need > > > > to do that. > > > > > > > > Would there be a way to ensure that the new s_version_max value has made > > > > it to disk? Bumping it by a large value and hoping for the best might be > > > > ok for most cases, but there are always outliers, so it might be > > > > worthwhile to make an i_version increment wait on that if necessary. > > > > > > How common are unclean shutdowns in practice? Do ex64/XFS/btrfs keep > > > counters in the superblocks for journal replays that can be read easily? > > > > > > Several useful i_version applications could be negatively impacted by > > > frequent i_version invalidation. > > > > > > > One would hope "not very often", but Oopses _are_ something that happens > > occasionally, even in very stable environments, and it would be best if > > what we're building can cope with them. > > I was wondering if such unclean shutdown events are associated with SSD > “unsafe shutdowns”, as identified by the SMART counter. I think those > aren't necessarily restricted to oopses or various forms of powerless > (maybe depending on file system/devicemapper configuration)? > > I admit it's possible that the file system is shut down cleanly before > the kernel requests the power-off state from the firmware, but the > underlying SSD is not. > Yeah filesystem integrity is mostly what we're concerned with here. I think most local filesystems effectively set a flag in the superblock that is cleared when the it's cleanly unmounted. If that flag is set when you go to mount then you know there was a crash. We'd probably key off of that in some way internally. -- Jeff Layton <jlayton@xxxxxxxxxx>
