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

[Max Reitz]

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...

Signed-off-by: Max Reitz <mre...@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