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

[Fam Zheng <famz@redhat.com>]

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.

> >>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