[PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided

[PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided

[Michal Novotny]

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Hello everybody,
I have created a patch for pygrub and I am sending it as an attachment. 
This patch mainly solves the issue of invalid default boot option in 
VM's configuration. If the entry doesn't exist, it doesn't exit with 
IndexError python exception but it uses first entry there to boot up the 
machine - same way like standard (real) grub does...

Signed-off-by: Michal Novotny <minovotn@redhat.com>

[-- Attachment #2: xen-pygrub-invalid-default-configuration.patch --]
[-- Type: text/plain, Size: 532 bytes --]

diff -r e1562a36094e tools/pygrub/src/pygrub
--- a/tools/pygrub/src/pygrub	Thu Mar 19 17:04:06 2009 +0000
+++ b/tools/pygrub/src/pygrub	Fri Mar 20 15:09:31 2009 +0100
@@ -530,7 +530,11 @@
         print "No kernel image selected!"
         sys.exit(1)
 
-    img = g.cf.images[sel]
+    try:
+        img = g.cf.images[sel]
+    except:
+        log.debug("PyGrub: Default selection is not valid, using first boot configuration...")
+        img = g.cf.images[0]
 
     grubcfg = { "kernel": None, "ramdisk": None, "args": None }
 

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Re: [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided

[Ian Jackson]

Michal Novotny writes ("[Xen-devel] [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided"):
> -    img = g.cf.images[sel]
> +    try:
> +        img = g.cf.images[sel]
> +    except:

It is not correct to do this on all exceptions.  (This is a common
mistake in Python.)  I assume that in your error case the images array
doesn't have the relevant entry and that your code should read:
  +        img = g.cf.images[sel]
  +    except KeyError:

Ian.

Re: [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided

[Michal Novotny]

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Hi,
thanks for advice. Here's new and corrected version of the patch. Well, 
the error here is IndexError, when an error occurs so the IndexError is 
catched and not KeyError. I have also tried it with KeyError but it was 
not working so IndexError is catched here.

Michal

Ian Jackson wrote:
> Michal Novotny writes ("[Xen-devel] [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided"):
>   
>> -    img = g.cf.images[sel]
>> +    try:
>> +        img = g.cf.images[sel]
>> +    except:
>>     
>
> It is not correct to do this on all exceptions.  (This is a common
> mistake in Python.)  I assume that in your error case the images array
> doesn't have the relevant entry and that your code should read:
>   +        img = g.cf.images[sel]
>   +    except KeyError:
>
> Ian.
>   


[-- Attachment #2: xen-pygrub-invalid-default-configuration.patch --]
[-- Type: text/plain, Size: 449 bytes --]

diff -r e1562a36094e tools/pygrub/src/pygrub
--- a/tools/pygrub/src/pygrub	Thu Mar 19 17:04:06 2009 +0000
+++ b/tools/pygrub/src/pygrub	Fri Mar 20 15:09:31 2009 +0100
@@ -530,7 +530,11 @@
         print "No kernel image selected!"
         sys.exit(1)
 
-    img = g.cf.images[sel]
+    try:
+        img = g.cf.images[sel]
+    except IndexError:
+        img = g.cf.images[0]
+
 
     grubcfg = { "kernel": None, "ramdisk": None, "args": None }
 

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Re: [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided

[Ian Jackson]

Michal Novotny writes ("Re: [Xen-devel] [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided"):
> thanks for advice. Here's new and corrected version of the patch. Well, 
> the error here is IndexError, when an error occurs so the IndexError is 
> catched and not KeyError. I have also tried it with KeyError but it was 
> not working so IndexError is catched here.

Err, yes, I didn't double-check with the docs or the rest of the
code.  Your version is very likely correct.

Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

Ian.