Summary of the question:
Should the topmost mount be visible, or should the most recent
mount be visible?
consider the following command sequence
(1) cd /mnt
(2) mount --bind /usr /mnt
(3) mount --bind /bin /mnt
(4) mount --bind /var .
after step 1, the pwd of the process is
Here is a scenario with shared subtree. Sorry it is complex.
mount --bind /mnt /mnt
mount --make-shared /mnt
mkdir -p /mnt/p
mount --bind /usr /mnt/1
mount --bind /mnt /mnt/2
At this stage the mount at /mnt/2 and /mnt belong to the same pnode
which means mounts under them propogate
On Thu, 2005-07-28 at 04:56, Miklos Szeredi wrote:
Here is a scenario with shared subtree. Sorry it is complex.
mount --bind /mnt /mnt
mount --make-shared /mnt
mkdir -p /mnt/p
mount --bind /usr /mnt/1
mount --bind /mnt /mnt/2
At this stage the mount at /mnt/2 and /mnt
step 1: mount --bind /mnt /mnt
a new mount 'A' is created at /mnt
step 2: mount --make-shared /mnt
mounts under 'A' are made shared. But in this case
there are no other mounts. So only 'A' will be made shared.
step 3: mkdir -p /mnt/1
I don't know enough about shared subtrees to have an opinion on what
should happen with those, but you fundamentally asked about a perceived
weirdness in existing Linux code, and I do have an opinion on that (which
is that there's no weirdness).
On analysis it turns out the culprit is the
I think the issue is what does mount F over directory D mean?
Does it mean to mount F immediately over D, in spite of anything that
might be stacked above D right now? Or does it mean to throw F onto the
stack which is currently sitting over D? Your analysis assumes it's the
former,
On Thu, 2005-07-28 at 12:30, Miklos Szeredi wrote:
no. there is no asymmetry as such. the propogations are working the way
they are meant to. But the confusion arises because of the mount lookup
symantics. The reason Avantika(who is doing shared subtree testing),
had this exact confusion
On Thu, 2005-07-28 at 13:35, Bryan Henderson wrote:
It wouldn't surprise me if someone is depending on mount over .. But
I'd be surprised if someone is doing it to a directory that's already been
mounted over (such that the stacking behavior is relevant). That seems
really eccentric.
I am not surprised when mounts on /mnt/1 do not propogate to /mnt/2/1
This is expected, and I am perfectly happy. Because the mount is
attempted on 'B' and 'B' has nobody to propogate to.
when mount on /mnt/2/1 (i.e on C at dentry 1) is attempted, I expect
to see a new mount 'E' at that
Does it mean to mount F immediately over D, in spite of anything that
might be stacked above D right now? Or does it mean to throw F onto
the
stack which is currently sitting over D? Your analysis assumes it's
the
former, whereas what Linux does is consistent with the latter.
Bryan, what would you expect the behavior to be when somebody mounts on
a directory what is already mounted over?
Well, I've tried to beg the question. I said I don't think it's
meaningful to mount over a directory; that one actually mounts at a name.
And that Linux's peculiar mount over '.'
One problem with 1) [mounting into the middle of a mount stack]
is that it breaks the assumption that an 'mount X;
umount X' pair is a no-op.
A very good point. Since unmounts are always from the top of the stack,
for symmetry mounts should be there too.
Here's another tidbit of information I
On Thu, 2005-07-28 at 15:27, Bryan Henderson wrote:
Bryan, what would you expect the behavior to be when somebody mounts on
a directory what is already mounted over?
Well, I've tried to beg the question. I said I don't think it's
meaningful to mount over a directory; that one actually
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