On 01/09/04 01:34, H. Peter Anvin wrote:
In many ways this returns to the simplicity of the autofs v3 design where the atomicity constraints where guaranteed by the VFS itself, *as long as* mount traps can be atomically destroyed with umounting the underlying filesystem.
Do we need to revive Tigran's forced unmount patch 'badfs' ala FreeBSD's deadfs? Although it doesn't guarantee atomic unmount, it could help a lot with the tendancy to get stuck autofs mounts.
http://tinyurl.com/2hto8
I've been long waiting for this functionality in mainline.
This is an interesting approach to killing off a mountpoint. However, the problem in question is not the destruction of the mountpoints, but rather being able to check_activity_of_a_hierarchy_of_mountpoints/unmount_them_together atomically. This cannot be done cleanly in userspace even when given an interface to do the check, someone can race in before userspace initiates the unmounts. The alternative is to have userspace detach the hierarchy of mountpoints using the '-l' option to umount(8), but then we may still unneccesarily unmount the filesystem will someone is in it.
I think that both HPA and I agree that this capability is needed in order to support lazy mounting of multimounts properly. The issue that remains is *how* to do it.
The time required to unmount something is constant if we detach the mountpoint using a lazy umount.
I wonder if binding badfs over the mountpoint at the beginning of the potentially lengthy unmount process would improve the atomicity to userspace. ie although the unmount would proceed in the background, badfs would have been mounted at that point at the start of the process - mounts are atomic no?
~mc
-- Mike Waychison Sun Microsystems, Inc. 1 (650) 352-5299 voice 1 (416) 202-8336 voice mailto: [EMAIL PROTECTED] http://www.sun.com
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