Re: mount: "nofail" and already mounted devices?

[Stanislav Brabec <sbrabec@suse.cz>]

Karel Zak wrote:
> On Wed, Jan 08, 2014 at 06:55:41PM +0100, Stanislav Brabec wrote:
> > Attempting to mount of already mounted devices is a common situation in
> > many scripts.
> 
> What about to fix the scripts? :-)
> 
> All you need is to call
> 
>     findmnt --source <dev> --target <mountpoint>

Yes, it is an option.

The new behavior could simplify common situation and also prevent a
race:
if the device is not yet mounted
   mount it
do the work

> > Would be acceptable a patch that adds "already mounted" to "nofail"?
> 
> Maybe.

Well, It could be a straightforward solution (~2 lines change). But it
could break following script (theoretical, a bit dumb and fragile, but
still depending only on documented behavior):

... do some actions that will initiate delayed $DEVICE creation ...
while mount -o nofail $DEVICE /opt ; do
  if test -d /opt/myvendor ; then
    break
  fi
  sleep 1
done

Now imagine, that somebody previously called:
mount $DEVICE /opt

What will happen with the current mount?
The script will fail as expected.

What will happen after such patch?
The script will enter to a dead loop.

> > - Make possible to use "-a" with further arguments.
> 
>   mount -a /foo /bar [...]
> 
> Right? 

Well, it sounds interesting as well, but I was thinking about
(conflicting):
mount -a /dev/device /mountpoint

It can be done both:

mount -a /foo /bar [...]
mount -A /dev/device /mountpoint

-A Do not report errors if the mount point is already used or device is
   already mounted.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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