On Thursday 02 November 2006 5:07 am, Ian Kent wrote:
> On Sat, 28 Oct 2006, Rob Landley wrote:
>
> > I'm trying to implement a df command that works based on /proc/mounts and
> > statvfs. To make this work, I need to be able to detect duplicate mounts
> > (including --bind mounts), and I need to be able to detect overmounted
> > filesystems.
>
> I need to do quite a bit with mount tables in autofs.
> You may wish to look at lib/mounts.c in autofs version 5.
I've fiddled with this area before (I wrote the current BusyBox mount
command), and after a day or so of banging on it I did eventually get it to
work.
It turns out that statvfs.f_fsid is completely useless. What you need to do
is a normal stat() on each path from /proc/mounts and look at the st_dev
member, which turns out to be unique for each mounted filesystem (including
tmpfs and /proc and /sys). So this lets you identify unique filesystems, and
then detecting --bind mounts and overmounts is just a question or matching up
the st_dev values.
The remaining question was, when there are multiple mount points statting to
the same st_dev, which one's path should df display for that filesystem when
you do a normal "df"? What I did is for each unique st_dev, look at the last
entry in /proc/mounts, find its block device string (returned by getmntent()
as mnt_fsname), and then back up to find the first entry with both the same
st_dev and the same block device string. Display that one, dump the rest.
(If it had a different block device it was an overmounted filesystem. If it
had the same block device but wasn't the first occurence, it was either a
duplicate mount or a --bind mounts.)
> Current state of play can be found in files located at
> http://www.kernel.org/pub/linux/daemons/autofs/v5.
In my case "http://landley.net/code/toybox/download/toybox-0.0.1.tar.bz2";,
which is at best "embryonic" but if you do "make && mv toybox df && ./df"
that one command should work. (It's got a loooooooong way to go, I know...)
Rob
--
"Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away." - Antoine de Saint-Exupery
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