Re: [Qemu-devel] [PATCH 1/7] block: correctly set the keep_read_only flag

[Kevin Wolf <kwolf@redhat.com>]

Am 05.09.2012 15:08, schrieb Jeff Cody:
> On 09/05/2012 08:47 AM, Kevin Wolf wrote:
>> Am 30.08.2012 20:47, schrieb Jeff Cody:
>>> I believe the bs->keep_read_only flag is supposed to reflect
>>> the initial open state of the device. If the device is initially
>>> opened R/O, then commit operations, or reopen operations changing
>>> to R/W, are prohibited.
>>>
>>> Currently, the keep_read_only flag is only accurate for the active
>>> layer, and its backing file. Subsequent images end up always having
>>> the keep_read_only flag set.
>>>
>>> For instance, what happens now:
>>>
>>> [  base  ]  kro = 1, ro = 1
>>>     |
>>>     v
>>> [ snap-1 ]  kro = 1, ro = 1
>>>     |
>>>     v
>>> [ snap-2 ]  kro = 0, ro = 1
>>>     |
>>>     v
>>> [ active ]  kro = 0, ro = 0
>>>
>>> What we want:
>>>
>>> [  base  ]  kro = 0, ro = 1
>>>     |
>>>     v
>>> [ snap-1 ]  kro = 0, ro = 1
>>>     |
>>>     v
>>> [ snap-2 ]  kro = 0, ro = 1
>>>     |
>>>     v
>>> [ active ]  kro = 0, ro = 0
>>>
>>> Signed-off-by: Jeff Cody <jcody@redhat.com>
>>> ---
>>>  block.c | 16 +++++++---------
>>>  block.h |  1 +
>>>  2 files changed, 8 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/block.c b/block.c
>>> index 470bdcc..e31b76f 100644
>>> --- a/block.c
>>> +++ b/block.c
>>> @@ -655,7 +655,7 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
>>>       * Clear flags that are internal to the block layer before opening the
>>>       * image.
>>>       */
>>> -    open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
>>> +    open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_ALLOW_RDWR);
>>>  
>>>      /*
>>>       * Snapshots should be writable.
>>> @@ -664,8 +664,6 @@ static int bdrv_open_common(BlockDriverState *bs, const char *filename,
>>>          open_flags |= BDRV_O_RDWR;
>>>      }
>>>  
>>> -    bs->keep_read_only = bs->read_only = !(open_flags & BDRV_O_RDWR);
>>> -
>>>      /* Open the image, either directly or using a protocol */
>>>      if (drv->bdrv_file_open) {
>>>          ret = drv->bdrv_file_open(bs, filename, open_flags);
>>> @@ -804,6 +802,12 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
>>>          goto unlink_and_fail;
>>>      }
>>>  
>>> +    if (flags & BDRV_O_RDWR) {
>>> +        flags |= BDRV_O_ALLOW_RDWR;
>>> +    }
>>> +
>>> +    bs->keep_read_only = !(flags & BDRV_O_ALLOW_RDWR);
>>
>> Do we still need bs->keep_read_only or is it duplicated in
>> bs->open_flags now? We can convert all users in a follow-up patch.
>>
> 
> I think we can ditch keep_read_only, and just use BDRV_O_ALLOW_RDWR.  The
> only other user of keep_read_only is the original bdrv_commit(), in
> block.c.  And, the natural way to convert that function would be to have
> it use bdrv_reopen(), to change from r/o->r/w.

Ah, yes, makes sense. So just using it in patch 2 and then converting
bdrv_commit() should be enough.

Kevin