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. The shutdown method is implemented only by block-based filesystems and arguably shutdown was always a misnomer because it assumed that the filesystem needs to actually shut down when it is called. IOW, we made it so that it is a call to action but that doesn't have to be the case. Calling it ->remove_bdev() is imo the correct thing because it gives block based filesystem the ability to handle device events how they see fit. Once we will have non-block based filesystems that need a method to always shut down the filesystem itself we might have to revisit this design anyway but no one had that use-case yet. > > Awkward naming is often a sign that further thought (or at least > separation of code) is needed. > > As an aside: > 'twould be nice if we could lift the *FS_IOC_SHUTDOWN dispatch out of > everyone's ioctl functions into the VFS, and then move the "I am dead" > state into super_block so that you could actually shut down any > filesystem, not just the seven that currently implement it. That goes back to my earlier point. Fwiw, I think that's valuable work. _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
