[Qemu-devel] Re: [PATCH 1/4] Add virtio disk identification support

[john cooper <john.cooper@redhat.com>]

Anthony Liguori wrote:
> On 03/25/2010 12:32 AM, john cooper wrote:
>> Add virtio-blk device id (s/n) support via virtio request.
>> Remove artifacts of pci and ATA_IDENTIFY implementation
>> relative to prior versions.
>>
>> Signed-off-by: john cooper<john.cooper@redhat.com>
>> ---
>>
>> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
>> index 9915840..358b0af 100644
>> --- a/hw/virtio-blk.c
>> +++ b/hw/virtio-blk.c
>> @@ -19,6 +19,8 @@
>>   # include<scsi/sg.h>
>>   #endif
>>
>> +#define min(a,b) ((a)<  (b) ? (a) : (b))
>>    
> 
> We already have MIN().
> 
>> +
>>   typedef struct VirtIOBlock
>>   {
>>       VirtIODevice vdev;
>> @@ -28,6 +30,7 @@ typedef struct VirtIOBlock
>>       QEMUBH *bh;
>>       BlockConf *conf;
>>       unsigned short sector_mask;
>> +    char sn[BLOCK_SERIAL_STRLEN];
>>   } VirtIOBlock;
>>
>>   static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
>> @@ -317,6 +320,12 @@ static void
>> virtio_blk_handle_request(VirtIOBlockReq *req,
>>           virtio_blk_handle_flush(req);
>>       } else if (req->out->type&  VIRTIO_BLK_T_SCSI_CMD) {
>>           virtio_blk_handle_scsi(req);
>> +    } else if (req->out->type&  VIRTIO_BLK_T_GET_ID) {
>> +        VirtIOBlock *s = req->dev;
>> +
>> +        memcpy(req->elem.in_sg[0].iov_base, s->sn,
>> +               min(req->elem.in_sg[0].iov_len, sizeof(s->sn)));
>> +        virtio_blk_req_complete(req, VIRTIO_BLK_S_OK);
>>       } else if (req->out->type&  VIRTIO_BLK_T_OUT) {
>>           qemu_iovec_init_external(&req->qiov,&req->elem.out_sg[1],
>>                                    req->elem.out_num - 1);
>> @@ -496,6 +505,8 @@ VirtIODevice *virtio_blk_init(DeviceState *dev,
>> BlockConf *conf)
>>       bdrv_guess_geometry(s->bs,&cylinders,&heads,&secs);
>>       bdrv_set_geometry_hint(s->bs, cylinders, heads, secs);
>>
>> +    strncpy(s->sn, drive_get_serial(s->bs), sizeof (s->sn));
>> +
>>    
> 
> Friends don't let friends use strncpy().
> 
> This actually will result in a non-NULL terminated string if
> drive_get_serial() returns a string larger than s->sn.  Use snprintf()
> instead.

That actually is the desired behavior here as a serial
string is of BLOCK_SERIAL_STRLEN bytes length maximum
and not assured to be nul terminated (legacy ATA convention).
snprintf() would cause us to lose the last string character
in the case the full BLOCK_SERIAL_STRLEN bytes were in use.

There are existing storage allocations of BLOCK_SERIAL_STRLEN + 1
in some cases but this appears as an internal convenience
and is not part of the serial string data.

-john

-- 
john.cooper@redhat.com