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

[Max Reitz <mreitz@redhat.com>]

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.

>> 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