Dne 3.8.2016 v 12:47 Karel Zak napsal(a):
On Tue, Aug 02, 2016 at 07:55:03PM +0200, Stanislav Brabec wrote:
Here is a patch set that is based on a "safe implementation of loop
reuse" patch set sent three weeks ago.
I think it makes sense to reuse loop device by mount(8), because the
goal is to mount FS and mount the same FS from two device may be
disaster, but I'm not sure about losetup.
Would be enough to keep it stupid and exit with error if the same
backing file is already used and require --force to create duplicate
loopdev?
if (!force && has_conflict(backing_file, ....))
err(EXIT_FAILURE, _("%s: already associated with %s"), ....);
That is why the patch is split to several parts. One adds conflict
check, another adds re-use.
But I think, that it is useful. With the patch, you just can call
"losetup --find --print loop.img" and don't care about the details. You
will (nearly) always get a loop device, new or re-used.
For example:
Imagine that you want to write a script to mount btrfs snapshot, and you
also want loopdev.
With the loop re-use feature:
#!/bin/sh
LOOPDEV=$(losetup --find --show /test.img)
fsck "$LOOPDEV"
mount -tbtrfs -osubvol=.snapshots/$1 $LOOPDEV /mnt/$1
Without the feature, r/w mount will cause data corruption,
and the correct script will require losetup --list output parsing.
I can imagine split of --force to two options:
--force: Ignore conflicts.
--new: Always allocate new loop device (the old behavior).
--
Best Regards / S pozdravem,
Stanislav Brabec
software developer
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