[v3,03/25] block: Add BDS.backing_overridden
diff mbox

Message ID 20161130011851.24696-4-mreitz@redhat.com
State New
Headers show

Commit Message

Max Reitz Nov. 30, 2016, 1:18 a.m. UTC
If the backing file is overridden, this most probably does change the
guest-visible data of a BDS. Therefore, we will need to consider this in
bdrv_refresh_filename().

Adding a new field to the BDS is not nice, but it is very simple and
exactly keeps track of whether the backing file has been overridden.

This commit adds a FIXME which will be remedied by a follow-up commit.
Until then, the respective piece of code will not result in any behavior
that is worse than what we currently have.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block.c                   | 13 +++++++++++++
 block/mirror.c            |  4 ++++
 blockdev.c                | 16 ++++++++++++++++
 include/block/block_int.h |  1 +
 4 files changed, 34 insertions(+)

Comments

Eric Blake Jan. 11, 2017, 7 p.m. UTC | #1
On 11/29/2016 07:18 PM, Max Reitz wrote:
> If the backing file is overridden, this most probably does change the
> guest-visible data of a BDS. Therefore, we will need to consider this in
> bdrv_refresh_filename().
> 
> Adding a new field to the BDS is not nice, but it is very simple and
> exactly keeps track of whether the backing file has been overridden.
> 
> This commit adds a FIXME which will be remedied by a follow-up commit.
> Until then, the respective piece of code will not result in any behavior
> that is worse than what we currently have.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---

> +++ b/include/block/block_int.h
> @@ -461,6 +461,7 @@ struct BlockDriverState {
>      char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
>                                      this file image */
>      char backing_format[16]; /* if non-zero and backing_file exists */
> +    bool backing_overridden; /* backing file has been specified by the user */

Should we group all of the bool in this struct so as to reduce its size
and improve cache locality?  But it's already clunky, so that may be
appropriate as a separate patch.

Reviewed-by: Eric Blake <eblake@redhat.com>
Max Reitz Jan. 11, 2017, 7:06 p.m. UTC | #2
On 11.01.2017 20:00, Eric Blake wrote:
> On 11/29/2016 07:18 PM, Max Reitz wrote:
>> If the backing file is overridden, this most probably does change the
>> guest-visible data of a BDS. Therefore, we will need to consider this in
>> bdrv_refresh_filename().
>>
>> Adding a new field to the BDS is not nice, but it is very simple and
>> exactly keeps track of whether the backing file has been overridden.
>>
>> This commit adds a FIXME which will be remedied by a follow-up commit.
>> Until then, the respective piece of code will not result in any behavior
>> that is worse than what we currently have.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
> 
>> +++ b/include/block/block_int.h
>> @@ -461,6 +461,7 @@ struct BlockDriverState {
>>      char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
>>                                      this file image */
>>      char backing_format[16]; /* if non-zero and backing_file exists */
>> +    bool backing_overridden; /* backing file has been specified by the user */
> 
> Should we group all of the bool in this struct so as to reduce its size
> and improve cache locality?  But it's already clunky, so that may be
> appropriate as a separate patch.
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>

Yep, makes sense, but we should do that in a separate patch.

(Or maybe we should fix the compiler to automatically do that
reordering? O:-))

Max

Patch
diff mbox

diff --git a/block.c b/block.c
index 1615f5d..438201d 100644
--- a/block.c
+++ b/block.c
@@ -1495,6 +1495,11 @@  int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     reference = qdict_get_try_str(parent_options, bdref_key);
     if (reference || qdict_haskey(options, "file.filename")) {
         backing_filename[0] = '\0';
+
+        /* FIXME: Should also be set to true if @options contains other runtime
+         *        options which control the data that is read from the backing
+         *        BDS */
+        bs->backing_overridden = true;
     } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
         QDECREF(options);
         goto free_exit;
@@ -1659,6 +1664,9 @@  static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
     bdrv_ref(bs_snapshot);
     bdrv_append(bs_snapshot, bs);
 
+    bs_snapshot->backing_overridden = true;
+    bdrv_refresh_filename(bs_snapshot);
+
     g_free(tmp_filename);
     return bs_snapshot;
 
@@ -1786,6 +1794,7 @@  static BlockDriverState *bdrv_open_inherit(const char *filename,
     backing = qdict_get_try_str(options, "backing");
     if (backing && *backing == '\0') {
         flags |= BDRV_O_NO_BACKING;
+        bs->backing_overridden = true;
         qdict_del(options, "backing");
     }
 
@@ -3959,6 +3968,10 @@  void bdrv_refresh_filename(BlockDriverState *bs)
      * refresh those first */
     QLIST_FOREACH(child, &bs->children, next) {
         bdrv_refresh_filename(child->bs);
+
+        if (child->role == &child_backing && child->bs->backing_overridden) {
+            bs->backing_overridden = true;
+        }
     }
 
     if (drv->bdrv_refresh_filename) {
diff --git a/block/mirror.c b/block/mirror.c
index 4ece624..6cb6cbd 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -891,6 +891,10 @@  static void mirror_complete(BlockJob *job, Error **errp)
 
         assert(!target->backing);
         bdrv_set_backing_hd(target, backing);
+
+        /* The target image's file already has been created with the backing
+         * file we just set, so there is no need to set backing_overridden or
+         * call bdrv_refresh_filename(). */
     }
 
     s->should_complete = true;
diff --git a/blockdev.c b/blockdev.c
index 245e1e1..7889bab 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1771,6 +1771,8 @@  static void external_snapshot_commit(BlkActionState *common)
 {
     ExternalSnapshotState *state =
                              DO_UPCAST(ExternalSnapshotState, common, common);
+    TransactionAction *action = common->action;
+    bool image_was_existing = false;
 
     bdrv_set_aio_context(state->new_bs, state->aio_context);
 
@@ -1783,6 +1785,20 @@  static void external_snapshot_commit(BlkActionState *common)
         bdrv_reopen(state->old_bs, state->old_bs->open_flags & ~BDRV_O_RDWR,
                     NULL);
     }
+
+    if (action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) {
+        BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data;
+        if (s->has_mode && s->mode == NEW_IMAGE_MODE_EXISTING) {
+            image_was_existing = true;
+        }
+    } else {
+        image_was_existing = true;
+    }
+
+    if (image_was_existing) {
+        state->new_bs->backing_overridden = true;
+        bdrv_refresh_filename(state->new_bs);
+    }
 }
 
 static void external_snapshot_abort(BlkActionState *common)
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 83a423c..555f3c2 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -461,6 +461,7 @@  struct BlockDriverState {
     char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
                                     this file image */
     char backing_format[16]; /* if non-zero and backing_file exists */
+    bool backing_overridden; /* backing file has been specified by the user */
 
     QDict *full_open_options;
     char exact_filename[PATH_MAX];