On Wed, Jul 09, 2025 at 08:37:05AM +0930, Qu Wenruo wrote: > 在 2025/7/9 08:29, Dave Chinner 写道: > > On Tue, Jul 08, 2025 at 09:55:14AM +0200, Christian Brauner wrote: > > > On Mon, Jul 07, 2025 at 05:45:32PM -0700, Darrick J. Wong wrote: > > > > On Tue, Jul 08, 2025 at 08:52:47AM +0930, Qu Wenruo wrote: > > > > > > > > > > > > > > > 在 2025/7/8 08:32, Dave Chinner 写道: > > > > > > On Fri, Jul 04, 2025 at 10:12:29AM +0930, Qu Wenruo wrote: > > > > > > > Currently all the filesystems implementing the > > > > > > > super_opearations::shutdown() callback can not afford losing a > > > > > > > device. > > > > > > > > > > > > > > Thus fs_bdev_mark_dead() will just call the shutdown() callback > > > > > > > for the > > > > > > > involved filesystem. > > > > > > > > > > > > > > But it will no longer be the case, with multi-device filesystems > > > > > > > like > > > > > > > btrfs and bcachefs the filesystem can handle certain device loss > > > > > > > without > > > > > > > shutting down the whole filesystem. > > > > > > > > > > > > > > To allow those multi-device filesystems to be integrated to use > > > > > > > fs_holder_ops: > > > > > > > > > > > > > > - Replace super_opearation::shutdown() with > > > > > > > super_opearations::remove_bdev() > > > > > > > To better describe when the callback is called. > > > > > > > > > > > > This conflates cause with action. > > > > > > > > > > > > The shutdown callout is an action that the filesystem must execute, > > > > > > whilst "remove bdev" is a cause notification that might require an > > > > > > action to be take. > > > > > > > > > > > > Yes, the cause could be someone doing hot-unplug of the block > > > > > > device, but it could also be something going wrong in software > > > > > > layers below the filesystem. e.g. dm-thinp having an unrecoverable > > > > > > corruption or ENOSPC errors. > > > > > > > > > > > > We already have a "cause" notification: blk_holder_ops->mark_dead(). > > > > > > > > > > > > The generic fs action that is taken by this notification is > > > > > > fs_bdev_mark_dead(). That action is to invalidate caches and shut > > > > > > down the filesystem. > > > > > > > > > > > > btrfs needs to do something different to a blk_holder_ops->mark_dead > > > > > > notification. i.e. it needs an action that is different to > > > > > > fs_bdev_mark_dead(). > > > > > > > > > > > > Indeed, this is how bcachefs already handles "single device > > > > > > died" events for multi-device filesystems - see > > > > > > bch2_fs_bdev_mark_dead(). > > > > > > > > > > I do not think it's the correct way to go, especially when there is > > > > > already > > > > > fs_holder_ops. > > > > > > > > > > We're always going towards a more generic solution, other than > > > > > letting the > > > > > individual fs to do the same thing slightly differently. > > > > > > > > On second thought -- it's weird that you'd flush the filesystem and > > > > shrink the inode/dentry caches in a "your device went away" handler. > > > > Fancy filesystems like bcachefs and btrfs would likely just shift IO to > > > > a different bdev, right? And there's no good reason to run shrinkers on > > > > either of those fses, right? > > > > > > > > > Yes, the naming is not perfect and mixing cause and action, but the > > > > > end > > > > > result is still a more generic and less duplicated code base. > > > > > > > > I think dchinner makes a good point that if your filesystem can do > > > > something clever on device removal, it should provide its own block > > > > device holder ops instead of using fs_holder_ops. I don't understand > > > > why you need a "generic" solution for btrfs when it's not going to do > > > > what the others do anyway. > > > > > > I think letting filesystems implement their own holder ops should be > > > avoided if we can. Christoph may chime in here. I have no appettite for > > > exporting stuff like get_bdev_super() unless absolutely necessary. We > > > tried to move all that handling into the VFS to eliminate a slew of > > > deadlocks we detected and fixed. I have no appetite to repeat that > > > cycle. > > > > Except it isn't actually necessary. > > > > Everyone here seems to be assuming that the filesystem *must* take > > an active superblock reference to process a device removal event, > > and that is *simply not true*. > > > > bcachefs does not use get_bdev_super() or an active superblock > > reference to process ->mark_dead events. > > Yes, bcachefs doesn't go this path, but the reason is more important. > > Is it just because there is no such callback so that Kent has to come up his > own solution, or something else? > > If the former case, all your argument here makes no sense. > > Adding Kent here to see if he wants a more generic s_op->remove_bdev() > solution or the current each fs doing its own mark_dead() callback.
Consider that the thing that has a block device open might not even be a filesystem, or at least a VFS filesystem. It could be a stacking block device driver - md or md - and those absolutely should be implementing .mark_dead() (likely passing it through on up the stack), or something else entirely. In bcachefs's case, we might not even have created the VFS super_block yet: we don't do that until after recovery finishes, and indeed we can't because creating a super_block and leaving it in !SB_BORN will cause such fun as sync calls to hang for the entire system... _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
