Re: [Qemu-devel] [PATCH v2 2/6] block: Add ImageInfoSpecific to BlockDriverInfo

[Max Reitz <mreitz@redhat.com>]

On 2013-09-10 09:50, Fam Zheng wrote:
> On Tue, 09/10 09:45, Max Reitz wrote:
>> On 2013-09-10 09:37, Fam Zheng wrote:
>>> On Tue, 09/10 09:22, Max Reitz wrote:
>>>> On 2013-09-10 05:26, Fam Zheng wrote:
>>>>> On Fri, 09/06 15:12, Max Reitz wrote:
>>>>>> Add the new ImageInfoSpecific type also to BlockDriverInfo.
>>>>>>
>>>>>> To prevent memory leaks, this field has to be initialized to NULL every
>>>>>> time before calling bdrv_get_info and qapi_free_ImageInfoSpecific has to
>>>>>> be called on it when the BlockDriverInfo object is no longer required.
>>>>>>
>>>>> I don't understand here. I think bdi is always passed into bdrv_get_info()
>>>>> uninitialized and in bdrv_get_info() there is:
>>>>>
>>>>>      memset(bdi, 0, sizeof(*bdi));
>>>>>
>>>>> before passing it on to driver, so it's always set to NULL.
>>>> Oh, you're right, I missed that. Thanks!
>>>>
>>>>> And why pointer, not a member to save a free() call?
>>>> As far as I understand it (and if I don't miss anything again),
>>>> ImageInfoSpecific is a auto-generated QAPI type, so it may contain
>>>> pointers to other types anyway (as it does in the case of QCow2,
>>>> which is the only driver where I have implemented this new field at
>>>> all; in that case, the compatiblity level is a string), therefore we
>>>> always need some function to clean up the data referenced by
>>>> ImageInfoSpecific; qapi_free_ImageInfoSpecific is the perfect one
>>>> for this, but it takes a heap pointer.
>>>>
>>>> Hence, I think using a pointer (to a heap-allocated object) is
>>>> easier in this case, since the QAPI clean-up function assumes this
>>>> case.
>>>>
>>> OK, learning this from you. Since this is allocated in bdrv_get_info() (from
>>> the caller PoV), and, the info requires releasing after use, a bdrv_put_info()
>>> may be a good function to do it, instead of directly operate on the field
>>> everywhere.
>> You mean a function for filling the ImageInfoSpecific field? Hm, we
>> can't really use parameters, since every driver would then require
>> its own function (which, imo, would defeat the purpose); the only
>> thing I can imagine right now is a function which converts a JSON
>> description to the object; however, this would again require proper
>> escaping for strings and conversion to strings for non-string types,
>> so I doubt whether this would really help...
>>
> No, I mean freeing it. Maybe I should suggest bdrv_free_info() or something
> else. It's just that too many
>
>      qapi_free_ImageInfoSpecific(bdi.format_specific);
>
> lines after all the bdrv_get_info() calls don't look very clean.
Sounds nice. I'll do it; thanks for the suggestion.

>>>>>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>>>>>> ---
>>>>>>   block.c               | 3 ++-
>>>>>>   block/mirror.c        | 6 ++++--
>>>>>>   block/qapi.c          | 6 +++++-
>>>>>>   include/block/block.h | 2 ++
>>>>>>   qemu-img.c            | 3 ++-
>>>>>>   qemu-io-cmds.c        | 6 +++++-
>>>>>>   6 files changed, 20 insertions(+), 6 deletions(-)
>>>>>>
>>>>>> diff --git a/block.c b/block.c
>>>>>> index 26639e8..1a5d2a4 100644
>>>>>> --- a/block.c
>>>>>> +++ b/block.c
>>>>>> @@ -1921,7 +1921,7 @@ void bdrv_round_to_clusters(BlockDriverState *bs,
>>>>>>                               int64_t *cluster_sector_num,
>>>>>>                               int *cluster_nb_sectors)
>>>>>>   {
>>>>>> -    BlockDriverInfo bdi;
>>>>>> +    BlockDriverInfo bdi = { .format_specific = NULL };
>>>>>>       if (bdrv_get_info(bs, &bdi) < 0 || bdi.cluster_size == 0) {
>>>>>>           *cluster_sector_num = sector_num;
>>>>>> @@ -1932,6 +1932,7 @@ void bdrv_round_to_clusters(BlockDriverState *bs,
>>>>>>           *cluster_nb_sectors = QEMU_ALIGN_UP(sector_num - *cluster_sector_num +
>>>>>>                                               nb_sectors, c);
>>>>>>       }
>>>>>> +    qapi_free_ImageInfoSpecific(bdi.format_specific);
>>>>>>   }
>>>>>>   static bool tracked_request_overlaps(BdrvTrackedRequest *req,
>>>>>> diff --git a/block/mirror.c b/block/mirror.c
>>>>>> index 86de458..cfef7e9 100644
>>>>>> --- a/block/mirror.c
>>>>>> +++ b/block/mirror.c
>>>>>> @@ -295,7 +295,7 @@ static void coroutine_fn mirror_run(void *opaque)
>>>>>>       BlockDriverState *bs = s->common.bs;
>>>>>>       int64_t sector_num, end, sectors_per_chunk, length;
>>>>>>       uint64_t last_pause_ns;
>>>>>> -    BlockDriverInfo bdi;
>>>>>> +    BlockDriverInfo bdi = { .format_specific = NULL };
>>>>>>       char backing_filename[1024];
>>>>>>       int ret = 0;
>>>>>>       int n;
>>>>>> @@ -325,6 +325,7 @@ static void coroutine_fn mirror_run(void *opaque)
>>>>>>               s->buf_size = MAX(s->buf_size, bdi.cluster_size);
>>>>>>               s->cow_bitmap = bitmap_new(length);
>>>>>>           }
>>>>>> +        qapi_free_ImageInfoSpecific(bdi.format_specific);
>>>>>>       }
>>>>>>       end = s->common.len >> BDRV_SECTOR_BITS;
>>>>>> @@ -544,13 +545,14 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
>>>>>>       if (granularity == 0) {
>>>>>>           /* Choose the default granularity based on the target file's cluster
>>>>>>            * size, clamped between 4k and 64k.  */
>>>>>> -        BlockDriverInfo bdi;
>>>>>> +        BlockDriverInfo bdi = { .format_specific = NULL };
>>>>>>           if (bdrv_get_info(target, &bdi) >= 0 && bdi.cluster_size != 0) {
>>>>>>               granularity = MAX(4096, bdi.cluster_size);
>>>>>>               granularity = MIN(65536, granularity);
>>>>>>           } else {
>>>>>>               granularity = 65536;
>>>>>>           }
>>>>>> +        qapi_free_ImageInfoSpecific(bdi.format_specific);
>>>>>>       }
>>>>>>       assert ((granularity & (granularity - 1)) == 0);
>>>>>> diff --git a/block/qapi.c b/block/qapi.c
>>>>>> index a4bc411..f13fbd5 100644
>>>>>> --- a/block/qapi.c
>>>>>> +++ b/block/qapi.c
>>>>>> @@ -110,7 +110,7 @@ void bdrv_query_image_info(BlockDriverState *bs,
>>>>>>       uint64_t total_sectors;
>>>>>>       const char *backing_filename;
>>>>>>       char backing_filename2[1024];
>>>>>> -    BlockDriverInfo bdi;
>>>>>> +    BlockDriverInfo bdi = { .format_specific = NULL };
>>>>>>       int ret;
>>>>>>       Error *err = NULL;
>>>>>>       ImageInfo *info = g_new0(ImageInfo, 1);
>>>>>> @@ -133,6 +133,10 @@ void bdrv_query_image_info(BlockDriverState *bs,
>>>>>>           }
>>>>>>           info->dirty_flag = bdi.is_dirty;
>>>>>>           info->has_dirty_flag = true;
>>>>>> +        if (bdi.format_specific) {
>>>>>> +            info->format_specific = bdi.format_specific;
>>>>>> +            info->has_format_specific = true;
>>>>>> +        }
>>>>>>       }
>>>>>>       backing_filename = bs->backing_file;
>>>>>>       if (backing_filename[0] != '\0') {
>>>>>> diff --git a/include/block/block.h b/include/block/block.h
>>>>>> index e6b391c..85e9703 100644
>>>>>> --- a/include/block/block.h
>>>>>> +++ b/include/block/block.h
>>>>>> @@ -18,6 +18,8 @@ typedef struct BlockDriverInfo {
>>>>>>       /* offset at which the VM state can be saved (0 if not possible) */
>>>>>>       int64_t vm_state_offset;
>>>>>>       bool is_dirty;
>>>>>> +    /* additional information; NULL if none */
>>>>>> +    ImageInfoSpecific *format_specific;
>>>>>>   } BlockDriverInfo;
>>>>>>   typedef struct BlockFragInfo {
>>>>>> diff --git a/qemu-img.c b/qemu-img.c
>>>>>> index b9a848d..ec1ecca 100644
>>>>>> --- a/qemu-img.c
>>>>>> +++ b/qemu-img.c
>>>>>> @@ -1125,7 +1125,7 @@ static int img_convert(int argc, char **argv)
>>>>>>       uint64_t bs_sectors;
>>>>>>       uint8_t * buf = NULL;
>>>>>>       const uint8_t *buf1;
>>>>>> -    BlockDriverInfo bdi;
>>>>>> +    BlockDriverInfo bdi = { .format_specific = NULL };
>>>>>>       QEMUOptionParameter *param = NULL, *create_options = NULL;
>>>>>>       QEMUOptionParameter *out_baseimg_param;
>>>>>>       char *options = NULL;
>>>>>> @@ -1369,6 +1369,7 @@ static int img_convert(int argc, char **argv)
>>>>>>               error_report("could not get block driver info");
>>>>>>               goto out;
>>>>>>           }
>>>>>> +        qapi_free_ImageInfoSpecific(bdi.format_specific);
>>>>>>           cluster_size = bdi.cluster_size;
>>>>>>           if (cluster_size <= 0 || cluster_size > IO_BUF_SIZE) {
>>>>>>               error_report("invalid cluster size");
>>>>>> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
>>>>>> index f91b6c4..563dd40 100644
>>>>>> --- a/qemu-io-cmds.c
>>>>>> +++ b/qemu-io-cmds.c
>>>>>> @@ -1677,7 +1677,7 @@ static const cmdinfo_t length_cmd = {
>>>>>>   static int info_f(BlockDriverState *bs, int argc, char **argv)
>>>>>>   {
>>>>>> -    BlockDriverInfo bdi;
>>>>>> +    BlockDriverInfo bdi = { .format_specific = NULL };
>>>>>>       char s1[64], s2[64];
>>>>>>       int ret;
>>>>>> @@ -1699,6 +1699,10 @@ static int info_f(BlockDriverState *bs, int argc, char **argv)
>>>>>>       printf("cluster size: %s\n", s1);
>>>>>>       printf("vm state offset: %s\n", s2);
>>>>>> +    if (bdi.format_specific) {
>>>>>> +        qapi_free_ImageInfoSpecific(bdi.format_specific);
>>>>>> +    }
>>>>>> +
>>>>>>       return 0;
>>>>>>   }
>>>>>> -- 
>>>>>> 1.8.3.1
>>>>>>
>>>>>>
>>>> Max
>> Max

Max