Patchwork [V4,5/5] block: make all steps in qmp_transaction() as callback

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Submitter Wayne Xia
Date May 2, 2013, 2:26 a.m.
Message ID <1367461606-7554-6-git-send-email-xiawenc@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/240886/
State New
Headers show

Comments

Wayne Xia - May 2, 2013, 2:26 a.m.
Make it easier to add other operations to qmp_transaction() by using
callbacks, with external snapshots serving as an example implementation
of the callbacks.

Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
---
 blockdev.c |   92 ++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 71 insertions(+), 21 deletions(-)
Eric Blake - May 3, 2013, 2:46 p.m.
On 05/01/2013 08:26 PM, Wenchao Xia wrote:
> Make it easier to add other operations to qmp_transaction() by using
> callbacks, with external snapshots serving as an example implementation
> of the callbacks.
> 
> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> ---
>  blockdev.c |   92 ++++++++++++++++++++++++++++++++++++++++++++++-------------
>  1 files changed, 71 insertions(+), 21 deletions(-)
> 

> +/*
> + * This structure must be arranged as first member in parent type, assuming

To me, "parent type" seems like the wrong relationship - in C++, the
parent type is the smaller type, and the child type is the larger type
that includes the parent type as its first member.  That is,
BlkTransationStates IS the parent type, and the comment would read
better as "first member in child type".

> + * that compiler will also arrange it to the same address with parent instance.
> + * Later it will be used in free().
> + */
> +struct BlkTransactionStates {
> +    BlockdevAction *action;
> +    const BdrvActionOps *ops;
> +    QSIMPLEQ_ENTRY(BlkTransactionStates) entry;
> +};
>  

>  
>      /* Now we are going to do the actual pivot.  Everything up to this point
>       * is reversible, but we are committed at this point */

Is this comment still correct, now that things are extensible, or should
you s/pivot/commit/?

If you do respin, I agree that s/rollback/abort/ might be a nicer name
for that particular callback.  But I'm also quite okay with using the
patch as-is without a respin (while I pointed out two possible comment
wording changes, they don't make or break the patch for me).

Reviewed-by: Eric Blake <eblake@redhat.com>
Wayne Xia - May 6, 2013, 2 a.m.
于 2013-5-3 22:46, Eric Blake 写道:
> On 05/01/2013 08:26 PM, Wenchao Xia wrote:
>> Make it easier to add other operations to qmp_transaction() by using
>> callbacks, with external snapshots serving as an example implementation
>> of the callbacks.
>>
>> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
>> ---
>>   blockdev.c |   92 ++++++++++++++++++++++++++++++++++++++++++++++-------------
>>   1 files changed, 71 insertions(+), 21 deletions(-)
>>
>
>> +/*
>> + * This structure must be arranged as first member in parent type, assuming
>
> To me, "parent type" seems like the wrong relationship - in C++, the
> parent type is the smaller type, and the child type is the larger type
> that includes the parent type as its first member.  That is,
> BlkTransationStates IS the parent type, and the comment would read
> better as "first member in child type".
>
>> + * that compiler will also arrange it to the same address with parent instance.
>> + * Later it will be used in free().
>> + */
>> +struct BlkTransactionStates {
>> +    BlockdevAction *action;
>> +    const BdrvActionOps *ops;
>> +    QSIMPLEQ_ENTRY(BlkTransactionStates) entry;
>> +};
>>
>
>>
>>       /* Now we are going to do the actual pivot.  Everything up to this point
>>        * is reversible, but we are committed at this point */
>
> Is this comment still correct, now that things are extensible, or should
> you s/pivot/commit/?
>
> If you do respin, I agree that s/rollback/abort/ might be a nicer name
> for that particular callback.  But I'm also quite okay with using the
> patch as-is without a respin (while I pointed out two possible comment
> wording changes, they don't make or break the patch for me).
>
> Reviewed-by: Eric Blake <eblake@redhat.com>
>
   I'll respin to fix comments and use "abort" as v5, thanks for your
reviewing!

Patch

diff --git a/blockdev.c b/blockdev.c
index 77adec8..87ed99e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -779,14 +779,43 @@  void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
 
 
 /* New and old BlockDriverState structs for group snapshots */
-typedef struct BlkTransactionStates {
+
+typedef struct BlkTransactionStates BlkTransactionStates;
+
+/* Only prepare() may fail. In a single transaction, only one of commit() or
+   rollback() will be called, clean() will always be called if it present. */
+typedef struct BdrvActionOps {
+    /* Size of state struct, in bytes. */
+    size_t instance_size;
+    /* Prepare the work, must NOT be NULL. */
+    void (*prepare)(BlkTransactionStates *common, Error **errp);
+    /* Commit the changes, must NOT be NULL. */
+    void (*commit)(BlkTransactionStates *common);
+    /* Rollback the changes on fail, can be NULL. */
+    void (*rollback)(BlkTransactionStates *common);
+    /* Clean up resource in the end, can be NULL. */
+    void (*clean)(BlkTransactionStates *common);
+} BdrvActionOps;
+
+/*
+ * This structure must be arranged as first member in parent type, assuming
+ * that compiler will also arrange it to the same address with parent instance.
+ * Later it will be used in free().
+ */
+struct BlkTransactionStates {
+    BlockdevAction *action;
+    const BdrvActionOps *ops;
+    QSIMPLEQ_ENTRY(BlkTransactionStates) entry;
+};
+
+/* external snapshot private data */
+typedef struct ExternalSnapshotStates {
+    BlkTransactionStates common;
     BlockDriverState *old_bs;
     BlockDriverState *new_bs;
-    QSIMPLEQ_ENTRY(BlkTransactionStates) entry;
-} BlkTransactionStates;
+} ExternalSnapshotStates;
 
-static void external_snapshot_prepare(BlockdevAction *action,
-                                      BlkTransactionStates *states,
+static void external_snapshot_prepare(BlkTransactionStates *common,
                                       Error **errp)
 {
     BlockDriver *proto_drv;
@@ -797,6 +826,9 @@  static void external_snapshot_prepare(BlockdevAction *action,
     const char *new_image_file;
     const char *format = "qcow2";
     enum NewImageMode mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
+    ExternalSnapshotStates *states =
+                             DO_UPCAST(ExternalSnapshotStates, common, common);
+    BlockdevAction *action = common->action;
 
     /* get parameters */
     g_assert(action->kind == BLOCKDEV_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC);
@@ -871,8 +903,11 @@  static void external_snapshot_prepare(BlockdevAction *action,
     }
 }
 
-static void external_snapshot_commit(BlkTransactionStates *states)
+static void external_snapshot_commit(BlkTransactionStates *common)
 {
+    ExternalSnapshotStates *states =
+                             DO_UPCAST(ExternalSnapshotStates, common, common);
+
     /* This removes our old bs from the bdrv_states, and adds the new bs */
     bdrv_append(states->new_bs, states->old_bs);
     /* We don't need (or want) to use the transactional
@@ -882,13 +917,24 @@  static void external_snapshot_commit(BlkTransactionStates *states)
                 NULL);
 }
 
-static void external_snapshot_rollback(BlkTransactionStates *states)
+static void external_snapshot_rollback(BlkTransactionStates *common)
 {
+    ExternalSnapshotStates *states =
+                             DO_UPCAST(ExternalSnapshotStates, common, common);
     if (states->new_bs) {
         bdrv_delete(states->new_bs);
     }
 }
 
+static const BdrvActionOps actions[] = {
+    [BLOCKDEV_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC] = {
+        .instance_size = sizeof(ExternalSnapshotStates),
+        .prepare  = external_snapshot_prepare,
+        .commit   = external_snapshot_commit,
+        .rollback = external_snapshot_rollback,
+    },
+};
+
 /*
  * 'Atomic' group snapshots.  The snapshots are taken as a set, and if any fail
  *  then we do not pivot any of the devices in the group, and abandon the
@@ -909,32 +955,31 @@  void qmp_transaction(BlockdevActionList *dev_list, Error **errp)
     /* We don't do anything in this loop that commits us to the snapshot */
     while (NULL != dev_entry) {
         BlockdevAction *dev_info = NULL;
+        const BdrvActionOps *ops;
 
         dev_info = dev_entry->value;
         dev_entry = dev_entry->next;
 
-        states = g_malloc0(sizeof(BlkTransactionStates));
+        assert(dev_info->kind < ARRAY_SIZE(actions));
+
+        ops = &actions[dev_info->kind];
+        states = g_malloc0(ops->instance_size);
+        states->ops = ops;
+        states->action = dev_info;
         QSIMPLEQ_INSERT_TAIL(&snap_bdrv_states, states, entry);
 
-        switch (dev_info->kind) {
-        case BLOCKDEV_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC:
-            external_snapshot_prepare(dev_info, states, errp);
-            if (error_is_set(&local_err)) {
-                error_propagate(errp, local_err);
-                goto delete_and_fail;
-            }
-            break;
-        default:
-            abort();
+        states->ops->prepare(states, &local_err);
+        if (error_is_set(&local_err)) {
+            error_propagate(errp, local_err);
+            goto delete_and_fail;
         }
-
     }
 
 
     /* Now we are going to do the actual pivot.  Everything up to this point
      * is reversible, but we are committed at this point */
     QSIMPLEQ_FOREACH(states, &snap_bdrv_states, entry) {
-        external_snapshot_commit(states);
+        states->ops->commit(states);
     }
 
     /* success */
@@ -946,10 +991,15 @@  delete_and_fail:
     * the original bs for all images
     */
     QSIMPLEQ_FOREACH(states, &snap_bdrv_states, entry) {
-        external_snapshot_rollback(states);
+        if (states->ops->rollback) {
+            states->ops->rollback(states);
+        }
     }
 exit:
     QSIMPLEQ_FOREACH_SAFE(states, &snap_bdrv_states, entry, next) {
+        if (states->ops->clean) {
+            states->ops->clean(states);
+        }
         g_free(states);
     }
 }