Quoting Christian Seiler (christ...@iwakd.de):
...
> + /* Read-only bind-mounting... In older kernels, doing that
> required
> + * to do one MS_BIND mount and then MS_REMOUNT|MS_RDONLY the
> same
> + * one. According to mount(2) manpage, MS_BIND honors MS_RDONLY
> from
> + * kernel 2.6.26 onwards. However, this apparently does not
> work on
> + * kernel 3.8.
I'm still not sure what is going on for you with this. Running with the
latest 3.11 userns-enabled kernel (at ppa:ubuntu-lxc/kernel), I can
still do
sudo mkdir /tmp/{a,b}
sudo mount -t tmpfs tmpfs /tmp/a
sudo mount --bind /tmp/a /tmp/b
sudo mount -o remount,bind,ro /tmp/b
and end up with /tmp/b roand /tmp/a rw. This works for me in 3.2, 3.8,
and userns-enabled 3.11.
> Unfortunately, on that very same kernel, doing the
> + * same trick as above doesn't seem to work either, there one
> needs
> + * to ALSO specify MS_BIND for the remount, otherwise the entire
> + * fs is remounted read-only or the mount fails because it's
> busy...
That's actually understandable - there are two things which both have
a readonly.vs.readwrite state - the vfsmount, and the superblock. If
you don't add MS_BIND, then you are requesting remount of the
superblock.
-serge
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