Re: [Qemu-devel] [v2 Patch 5/9]block: qcow2 image file reopen

[Jeff Cody <jcody@redhat.com>]

On 07/30/2012 05:35 PM, Supriya Kannery wrote:
> qcow2 driver changes for bdrv_reopen_xx functions to
> safely reopen image files. Reopening of image files while
> changing hostcache dynamically is handled here.
> 
> Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>
> 
> ---
> Index: qemu/block/qcow2.c
> ===================================================================
> --- qemu.orig/block/qcow2.c
> +++ qemu/block/qcow2.c
> @@ -52,10 +52,19 @@ typedef struct {
>      uint32_t magic;
>      uint32_t len;
>  } QCowExtension;
> +
> +typedef struct BDRVQcowReopenState {
> +    BDRVReopenState reopen_state;
> +    BDRVQcowState *stash_s;
> +} BDRVQcowReopenState;
> +
>  #define  QCOW2_EXT_MAGIC_END 0
>  #define  QCOW2_EXT_MAGIC_BACKING_FORMAT 0xE2792ACA
>  #define  QCOW2_EXT_MAGIC_FEATURE_TABLE 0x6803f857
>  
> +static void qcow2_stash_state(BDRVQcowState *stashed_state, BDRVQcowState *s);
> +static void qcow2_revert_state(BDRVQcowState *s, BDRVQcowState *stashed_state);
> +
>  static int qcow2_probe(const uint8_t *buf, int buf_size, const char *filename)
>  {
>      const QCowHeader *cow_header = (const void *)buf;
> @@ -434,6 +443,169 @@ static int qcow2_open(BlockDriverState *
>      return ret;
>  }
>  
> +static int qcow2_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs,
> +                               int flags)
> +{
> +    BDRVQcowReopenState *qcow2_rs = g_malloc0(sizeof(BDRVQcowReopenState));
> +    int ret = 0;
> +    BDRVQcowState *s = bs->opaque;
> +
> +    qcow2_rs->reopen_state.bs = bs;
> +
> +    /* save state before reopen */
> +    qcow2_rs->stash_s = g_malloc0(sizeof(BDRVQcowState));
> +    qcow2_stash_state(qcow2_rs->stash_s, s);
> +    *prs = &(qcow2_rs->reopen_state);
> +
> +    /* Reopen file with new flags */
> +     ret = qcow2_open(bs, flags);
> +     return ret;
> +}
> +
> +static void qcow2_reopen_commit(BlockDriverState *bs, BDRVReopenState *rs)
> +{
> +    BDRVQcowReopenState *qcow2_rs;
> +    BDRVQcowState *stashed_s;
> +
> +    qcow2_rs = container_of(rs, BDRVQcowReopenState, reopen_state);
> +    stashed_s = qcow2_rs->stash_s;
> +
> +    qcow2_cache_flush(bs, stashed_s->l2_table_cache);
> +    qcow2_cache_flush(bs, stashed_s->refcount_block_cache);
> +
> +    qcow2_cache_destroy(bs, stashed_s->l2_table_cache);
> +    qcow2_cache_destroy(bs, stashed_s->refcount_block_cache);
> +
> +    g_free(stashed_s->unknown_header_fields);
> +    cleanup_unknown_header_ext(bs);
> +
> +    g_free(stashed_s->cluster_cache);
> +    qemu_vfree(stashed_s->cluster_data);



> +    qcow2_refcount_close(bs);
> +    qcow2_free_snapshots(bs);

I assume these are unintentional?  I believe this is what is causing your
double-free issue.

> +
> +    g_free(stashed_s);
> +    g_free(qcow2_rs);
> +}
> +
> +static void qcow2_reopen_abort(BlockDriverState *bs, BDRVReopenState *rs)
> +{
> +    BDRVQcowReopenState *qcow2_rs;
> +    BDRVQcowState *s = bs->opaque;
> +    BDRVQcowState *stashed_s;
> +
> +    qcow2_rs = container_of(rs, BDRVQcowReopenState, reopen_state);
> +
> +    /* Revert to stashed state */
> +    qcow2_revert_state(s, qcow2_rs->stash_s);
> +    stashed_s = qcow2_rs->stash_s;
> +
> +    g_free(stashed_s);
> +    g_free(qcow2_rs);
> +}
> +
> +static void qcow2_stash_state(BDRVQcowState *stashed_s, BDRVQcowState *s)
> +{
> +    stashed_s->cluster_bits = s->cluster_bits;
> +    stashed_s->cluster_size = s->cluster_size;
> +    stashed_s->cluster_sectors = s->cluster_sectors;
> +    stashed_s->l2_bits = s->l2_bits;
> +    stashed_s->l2_size = s->l2_size;
> +    stashed_s->l1_size = s->l1_size;
> +    stashed_s->l1_vm_state_index = s->l1_vm_state_index;
> +    stashed_s->csize_shift = s->csize_shift;
> +    stashed_s->csize_mask = s->csize_mask;
> +    stashed_s->cluster_offset_mask = s->cluster_offset_mask;
> +    stashed_s->l1_table_offset = s->l1_table_offset;
> +    stashed_s->l1_table = s->l1_table;
> +
> +    stashed_s->l2_table_cache = s->l2_table_cache;
> +    stashed_s->refcount_block_cache = s->refcount_block_cache;
> +
> +    stashed_s->cluster_cache = s->cluster_cache;
> +    stashed_s->cluster_data = s->cluster_data;
> +    stashed_s->cluster_cache_offset = s->cluster_cache_offset;
> +    stashed_s->cluster_allocs = s->cluster_allocs;
> +
> +    stashed_s->refcount_table = s->refcount_table;
> +    stashed_s->refcount_table_offset = s->refcount_table_offset;
> +    stashed_s->refcount_table_size = s->refcount_table_size;
> +    stashed_s->free_cluster_index = s->free_cluster_index;
> +    stashed_s->free_byte_offset = s->free_byte_offset;
> +
> +    stashed_s->lock = s->lock;
> +
> +    stashed_s->crypt_method = s->crypt_method;
> +    stashed_s->crypt_method_header = s->crypt_method_header;
> +    stashed_s->aes_encrypt_key = s->aes_encrypt_key;
> +    stashed_s->aes_decrypt_key = s->aes_decrypt_key;
> +    stashed_s->snapshots_offset = s->snapshots_offset;
> +    stashed_s->snapshots_size = s->snapshots_size;
> +    stashed_s->nb_snapshots = s->nb_snapshots;
> +    stashed_s->snapshots = s->snapshots;
> +
> +    stashed_s->flags = s->flags;
> +    stashed_s->qcow_version = s->qcow_version;
> +
> +    stashed_s->incompatible_features = s->incompatible_features;
> +    stashed_s->compatible_features = s->compatible_features;
> +
> +    stashed_s->unknown_header_fields_size = s->unknown_header_fields_size;
> +    stashed_s->unknown_header_fields = s->unknown_header_fields;
> +    stashed_s->unknown_header_ext = s->unknown_header_ext;
> +
> +}
> +
> +static void qcow2_revert_state(BDRVQcowState *s, BDRVQcowState *stashed_s)
> +{
> +   s->cluster_bits = stashed_s->cluster_bits;
> +   s->cluster_size = stashed_s->cluster_size;
> +   s->cluster_sectors = stashed_s->cluster_sectors;
> +   s->l2_bits = stashed_s->l2_bits;
> +   s->l2_size = stashed_s->l2_size;
> +   s->l1_size = stashed_s->l1_size;
> +   s->l1_vm_state_index = stashed_s->l1_vm_state_index;
> +   s->csize_shift = stashed_s->csize_shift;
> +   s->csize_mask = stashed_s->csize_mask;
> +   s->cluster_offset_mask = stashed_s->cluster_offset_mask;
> +   s->l1_table_offset = stashed_s->l1_table_offset;
> +   s->l1_table = stashed_s->l1_table;
> +   s->l2_table_cache = stashed_s->l2_table_cache;
> +   s->refcount_block_cache = stashed_s->refcount_block_cache;
> +
> +   s->cluster_cache = stashed_s->cluster_cache;
> +   s->cluster_data = stashed_s->cluster_data;
> +   s->cluster_cache_offset = stashed_s->cluster_cache_offset;
> +   s->cluster_allocs = stashed_s->cluster_allocs;
> +
> +   s->refcount_table = stashed_s->refcount_table;
> +   s->refcount_table_offset = stashed_s->refcount_table_offset;
> +   s->refcount_table_size = stashed_s->refcount_table_size;
> +   s->free_cluster_index = stashed_s->free_cluster_index;
> +   s->free_byte_offset = stashed_s->free_byte_offset;
> +
> +   s->lock = stashed_s->lock;
> +
> +   s->crypt_method = stashed_s->crypt_method;
> +   s->crypt_method_header = stashed_s->crypt_method_header;
> +   s->aes_encrypt_key = stashed_s->aes_encrypt_key;
> +   s->aes_decrypt_key = stashed_s->aes_decrypt_key;
> +   s->snapshots_offset = stashed_s->snapshots_offset;
> +   s->snapshots_size = stashed_s->snapshots_size;
> +   s->nb_snapshots = stashed_s->nb_snapshots;
> +   s->snapshots = stashed_s->snapshots;
> +
> +   s->flags = stashed_s->flags;
> +   s->qcow_version = stashed_s->qcow_version;
> +
> +   s->incompatible_features = stashed_s->incompatible_features;
> +   s->compatible_features = stashed_s->compatible_features;
> +
> +   s->unknown_header_fields_size = stashed_s->unknown_header_fields_size;
> +   s->unknown_header_fields = stashed_s->unknown_header_fields;
> +   s->unknown_header_ext = stashed_s->unknown_header_ext;
> +}
> +
>  static int qcow2_set_key(BlockDriverState *bs, const char *key)
>  {
>      BDRVQcowState *s = bs->opaque;
> @@ -1567,6 +1739,9 @@ static BlockDriver bdrv_qcow2 = {
>      .instance_size      = sizeof(BDRVQcowState),
>      .bdrv_probe         = qcow2_probe,
>      .bdrv_open          = qcow2_open,
> +    .bdrv_reopen_prepare = qcow2_reopen_prepare,
> +    .bdrv_reopen_commit = qcow2_reopen_commit,
> +    .bdrv_reopen_abort  = qcow2_reopen_abort,
>      .bdrv_close         = qcow2_close,
>      .bdrv_create        = qcow2_create,
>      .bdrv_co_is_allocated = qcow2_co_is_allocated,
> 
>