[Xen-devel] multiple mount protection

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

Through my own absent mindedness, I keep getting bitten with mounting
filesystems more than once and breaking them. Xen is good in that it
won't start a domain if it detects that one of its filesystems is
already mounted, but only on that physical machine - there are many
other ways I can go wrong!

Are there any filesystems which natively support protection for multiple
mounts? I can't quite imagine how such a thing might work... probably
via a 'scratch pad' where if the filesystem appears to be mounted, the
new mountee would set a flag there and wait for a pre-determined time
(say, 10 seconds), in which time the current mountee (if one existed)
would have reset the flag. If the flag remains set for the
pre-determined time, the new mountee can assume that there was an
unclean unmount (eg crash) and that journal recovery can be commenced.
Block device caching would have to be taken into account, which may be
the bit that makes it unworkable. But even if the possibility of a race
condition exists, it would still probably save me most of the time :)

James

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