Re: [BUG] grub-install fails on devices with high minor numbers

[Tim Walberg]

On 11/06/2015 21:26 +0300, Andrei Borzenkov wrote:
>>      06.11.2015 19:08, Tim Walberg ??????????:
>>      >On some relatively large systems that are used for virtualization,
>>      >often containing upwards of 100 virtual machines, we've started running
>>      >into issues with GRUB not being able to install on a new virtual 
>> machine
>>      >(using the typical process of mounting all the VM file systems on the 
>> host
>>      >and running grub-install under chroot). We've tracked the issue down 
>> to this
>>      >code, which is clearly erroneous - device minor numbers have been more 
>> than
>>      >8 bits for quite some time now - in 
>> grub-core/osdep/devmapper/getroot.c:
>>      >
>>      >     char *
>>      >     grub_util_devmapper_part_to_disk (struct stat *st,
>>      >                                   int *is_part, const char *path)
>>      >     {
>>      >       int major, minor;
>>      >
>>      >       if (grub_util_get_dm_node_linear_info (st->st_rdev,
>>      >                                          &major, &minor, 0))
>>      >         {
>>      >           *is_part = 1;
>>      >           return grub_find_device ("/dev",
>>      >                                    (major << 8) | minor);         
>> <<<<< --------- ERROR!
>>      >         }
>>      >       *is_part = 0;
>>      >       return xstrdup (path);
>>      >     }
>>      >
>>      >When we have enough device-mapper devices (including all their 
>> partitions)
>>      >on a host that the next newly-added set of devices ends up with minor 
>> numbers
>>      >outside the 8-bit range, this code fails, with the result that 
>> grub-install
>>      >can't find the devices that it needs to complete the install.
>>      >
>>      >There might be other places in the code where similar assumptions are 
>> made.
>>      >Someone more familiar with the code would probably be better for 
>> tracking
>>      >those down. But, this one at least needs to be fixed.
>>      >
>>      
>>      
>>      Does attached patch help?

>>      From: Andrei Borzenkov <address@hidden>
>>      Subject: [PATCH] devmapper/getroot: use makedev instead of direct shift
>>      
>>      Fixes device detection with large number of devices.
>>      
>>      Reported by Tim Wallberg <address@hidden>
>>      
>>      ---
>>       grub-core/osdep/devmapper/getroot.c | 3 +--
>>       1 file changed, 1 insertion(+), 2 deletions(-)
>>      
>>      diff --git a/grub-core/osdep/devmapper/getroot.c 
>> b/grub-core/osdep/devmapper/getroot.c
>>      index 0a77a04..64419f6 100644
>>      --- a/grub-core/osdep/devmapper/getroot.c
>>      +++ b/grub-core/osdep/devmapper/getroot.c
>>      @@ -208,8 +208,7 @@ grub_util_devmapper_part_to_disk (struct stat *st,
>>                                               &major, &minor, 0))
>>           {
>>             *is_part = 1;
>>      -      return grub_find_device ("/dev",
>>      -                              (major << 8) | minor);
>>      +      return grub_find_device ("/dev", makedev (major, minor));
>>           }
>>         *is_part = 0;
>>         return xstrdup (path);
>>      -- 
>>      tg: (cd6d79c..) u/makedev (depends on: master)

End of included message


Yes, that appears to have resolved the issue. I was already testing essentially
that patch on my own, but wasn't sure if there might be similar assumptions
made elsewhere in the code. This single fix handles at least the use case we
were having issues with.

            Thanks!
                  tw


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