Re: [Qemu-devel] [PATCH] Avoid divide by zero when there is no block device to migrate

[Pierre Riteau]

On 11 janv. 2011, at 12:54, Kevin Wolf wrote:

> Am 25.12.2010 21:52, schrieb Pierre Riteau:
>> When block migration is requested and no read-write block device is
>> present, a divide by zero exception is triggered because
>> total_sector_sum equals zero.
>> 
>> Signed-off-by: Pierre Riteau <address@hidden>
> 
> Maybe in this case we should generate an error before actually starting
> with block migration. If you bothered to request block migration you
> certainly didn't have in mind to do nothing.

I had in mind a scenario where a management system would use block migration 
all the time, regardless of what kind of devices were plugged in the VM.
If we throw an error, should it be a fatal error? Or just a migration failed 
result given to the monitor?

>> ---
>> block-migration.c |    6 +++++-
>> 1 files changed, 5 insertions(+), 1 deletions(-)
>> 
>> diff --git a/block-migration.c b/block-migration.c
>> index 1475325..d62d63e 100644
>> --- a/block-migration.c
>> +++ b/block-migration.c
>> @@ -350,7 +350,11 @@ static int blk_mig_save_bulked_block(Monitor *mon, 
>> QEMUFile *f)
>>         }
>>     }
>> 
>> -    progress = completed_sector_sum * 100 / 
>> block_mig_state.total_sector_sum;
>> +    if (block_mig_state.total_sector_sum != 0) {
>> +        progress = completed_sector_sum * 100 / 
>> block_mig_state.total_sector_sum;
> 
> This exceeds 80 characters per line.
> 
>> +    } else {
>> +        progress = 100;
>> +    }
>>     if (progress != block_mig_state.prev_progress) {
>>         block_mig_state.prev_progress = progress;
>>         qemu_put_be64(f, (progress << BDRV_SECTOR_BITS)
> 
> Kevin

-- 
Pierre Riteau -- PhD student, Myriads team, IRISA, Rennes, France
http://perso.univ-rennes1.fr/pierre.riteau/