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Re: [Xen-devel] [PATCH v4 3/4] libxl: call hotplug scripts from libxl for vbd

Roger Pau Monne writes ("Re: [Xen-devel] [PATCH v4 3/4] libxl: call hotplug 
scripts from libxl for vbd"):
> Ian Jackson escribió:
> > Wouldn't it be better to have an env var set by libxl to mean "_not_
> > called from udev?".  That would mean that if the udev rules weren't
> > updated for some reason it would all still work.  On many setups these
> > are config files which may require the user to merge changes, etc., so
> > this is a real concern.
> Since the 4.2 release already implies updating udev rules (due to the 
> change from tap* to *emu), I think it's better to set the var on udev, 
> that way when udev is dropped we won't need to perform any change to libxl.

Ah.  (The change to libxl is not an essential one so we won't "need"
to make it, but OK.)

> >> +if [ -n "${UDEV_CALL}" ]&&  \
> >> +   `xenstore-read "libxl/disable_udev">/dev/null 2>&1`; then
> >
> > This reads something from xenstore and executes it as a shell command!
> > (Also it will go wrong if the value read is empty eg becaue the key
> > doesn't exist.)
> Are you sure about this? This command never returns anything, because it 
> is redirected to /dev/null, so we only evaluate if it is able to read 
> libxl/disable_udev. If libxl/disable_udev exists this test is passed.

Uh, so it does.  Why are you using `` at all then ?  This is a very
odd construction.


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