Re: [Xen-devel] [PATCH] libxl: fix cleanup of tap devices in libxl__device_destroy

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-08-02 at 15:41 +0100, Ian Jackson wrote:
> Ian Campbell writes ("[PATCH] libxl: fix cleanup of tap devices in 
> libxl__device_destroy"):
> > libxl: fix cleanup of tap devices in libxl__device_destroy
> > 
> > We pass be_path to tapdisk_destroy but we've already deleted it so it fails 
> > to
> > read tapdisk-params. However it appears that we need to destroy the tap 
> > device
> > after tearing down xenstore, to avoid the leak reported by Greg Wettstein in
> > <201207312141.q6VLfJje012656@xxxxxxxxxxxxxxxxx>.
> > 
> > So read the tapdisk-params in the cleanup transaction, before the remove, 
> > and
> > pass that down to destroy_tapdisk instead. tapdisk-params may of course be 
> > NULL
> > if the device isn't a tap device.
> > 
> > There is no need to tear down the tap device from 
> > libxl__initiate_device_remove
> > since this ultimately calls libxl__device_destroy.
> > 
> > Propagate and log errors from libxl__device_destroy_tapdisk.
> 
> Can you please wrap your commit messages to 70ish rather than 80 ?
> Here is a screenshot of my email client:
>   http://www.chiark.greenend.org.uk/~ijackson/volatile/2012/wrap-damage.png
> 
> The code all looks good.  Just one comment:
> 
> >  int libxl__device_destroy(libxl__gc *gc, libxl__device *dev)
> >  {
> ...
> > @@ -531,6 +533,9 @@ int libxl__device_destroy(libxl__gc *gc,
> >          rc = libxl__xs_transaction_start(gc, &t);
> >          if (rc) goto out;
> >  
> > +        /* May not exist if this is not a tap device */
> > +        tapdisk_params = libxl__xs_read(gc, t, tapdisk_path);
> 
> You can still use libxl__xs_read_checked.  It considers ENOENT a
> success (and therefore doesn't log about it).

tapdisk_params cannot be const as read_checked requires because
tapdisk_destroy modified the string. I suppose I could add a strdup
inside.


> 
> Ian.



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