mount --bind behaviour

[Matthias Koenig <mkoenig@xxxxxxx>]

Hi,

As far as my understanding of bind mounts is, that they get the mount
options of the source and cannot have different mount options.
This is what is stated in mount(2): 
"The filesystemtype, mountflags, and data arguments are ignored."

Lets say we have /test and bind mount it to /mnt
# mount --bind /test /mnt
# mount
/test on /mnt type none (rw,bind)

Now some people have the idea to do the bind mount read-only, of course
this is not possible since the mount syscall ignores additional options.
But:
# mount --bind -r /test /mnt
# mount
/test on /mnt type none (ro,bind)

The mount *program* thinks the mount is ro, which is opposite to
what /proc/mounts states:
# cat /proc/mounts
/dev/sda3 /mnt ext3 rw,data=ordered 0 0

We cannot just ignore additional options in mount, because the source
could have been mounted with different options (e.g. ro).
I think we will have to clone the options of the source in case
of bind mounts.

Matthias
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