Am 18.02.2011 schrieb Miklos Szeredi:
>> The docs say (man 2 umount):
>> MNT_FORCE (since Linux 2.1.116)
>> Force unmount even if busy. This can cause data loss. (Only
>> for NFS mounts.)
>>
>> So the -f flag should only make a difference if a filesystem is busy,
>> and even then it should not affect other mount points.
>
> That's your interpretation, but the fact is, Linux doesn't work that
> way.
>
>> I'm not unmounting the original mount and complain that the bind mount
>> no longer works (that would in fact make sense with umount -f). It's the
>> other way around: I'm unmounting something that happens to bind mount a
>> directory lying on an sshfs file system to somewhere else and it causes
>> the underlying mount to break ("mount" still lists the mount to be
>> active, and so does "/proc/mounts").
>
> There's no distinction between original mount and bind mount in Linux.
> From the kernel's point of view they are completely equal.
If this is true and the way it is supposed to be, why don't we see the
same behaviour with an ext4 mount, for example:
---
/mnt# dd if=/dev/zero of=bigfile count=10240 bs=1024
/mnt# mkfs.ext4 bigfile
/mnt# mkdir -p mp1 mp2
/mnt# mount -o loop -t ext4 bigfile mp1
/mnt# mount -o bind mp1 mp2
/mnt# touch mp1/x
/mnt# ls mp2
lost+found x
/mnt# ls mp1
lost+found x
/mnt# umount -f mp2
/mnt# ls mp1
lost+found x
---
Regards
Johannes
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