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. 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. --D > > Hence Btrfs should be doing the same thing as bcachefs. The > > bdev_handle_ops structure exists precisly because it allows the > > filesystem to handle block device events in the exact manner they > > require.... > > > > > - Add a new @bdev parameter to remove_bdev() callback > > > To allow the fs to determine which device is missing, and do the > > > proper handling when needed. > > > > > > For the existing shutdown callback users, the change is minimal. > > > > Except for the change in API semantics. ->shutdown is an external > > shutdown trigger for the filesystem, not a generic "block device > > removed" notification. > > The problem is, there is no one utilizing ->shutdown() out of > fs_bdev_mark_dead(). > > If shutdown ioctl is handled through super_operations::shutdown, it will be > more meaningful to split shutdown and dev removal. > > But that's not the case, and different fses even have slightly different > handling for the shutdown flags (not all fses even utilize journal to > protect their metadata). > > Thanks, > Qu > > > > > > Hooking blk_holder_ops->mark_dead means that btrfs can also provide > > a ->shutdown implementation for when something external other than a > > block device removal needs to shut down the filesystem.... > > > > -Dave. > _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
