[Qemu-devel] [PATCH V2] disable blkverify external snapshot creation

[Qemu-devel] [PATCH V2] disable blkverify external snapshot creation

[Benoît Canet]

Hello,

Here is V2 of the external snapshot disabling patch.
The result is hopefully smaller and don't impact all BlockDriver anymore.
Only the blkverify Driver is modified.

v2:
   Use NULL fields to avoid having to fill the new field in every BlockDriver
       [Jeff]
   Rename the field [Kevin]

Benoît Canet (1):
  block: Add BlockDriver.bdrv_check_ext_snapshot.

 block.c                   | 14 ++++++++++++++
 block/blkverify.c         |  2 ++
 blockdev.c                |  5 +++++
 include/block/block.h     |  7 +++++++
 include/block/block_int.h |  8 ++++++++
 5 files changed, 36 insertions(+)

-- 
1.8.1.2

[Qemu-devel] [PATCH V2] block: Add BlockDriver.bdrv_check_ext_snapshot.

[Benoît Canet]

This field is used by blkverify to disable external snapshots creation.
I will also be used by block filters like quorum to disable external snapshots
creation.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 block.c                   | 14 ++++++++++++++
 block/blkverify.c         |  2 ++
 blockdev.c                |  5 +++++
 include/block/block.h     |  7 +++++++
 include/block/block_int.h |  8 ++++++++
 5 files changed, 36 insertions(+)

diff --git a/block.c b/block.c
index 4833b37..4da6fd9 100644
--- a/block.c
+++ b/block.c
@@ -4632,3 +4632,17 @@ int bdrv_amend_options(BlockDriverState *bs, QEMUOptionParameter *options)
     }
     return bs->drv->bdrv_amend_options(bs, options);
 }
+
+bool bdrv_check_ext_snapshot(BlockDriverState *bs)
+{
+    /* external snashots are enabled by defaults */
+    if (!bs->drv->bdrv_check_ext_snapshot) {
+        return true;
+    }
+    return bs->drv->bdrv_check_ext_snapshot(bs);
+}
+
+bool bdrv_forbid_ext_snapshot(BlockDriverState *bs)
+{
+    return false;
+}
diff --git a/block/blkverify.c b/block/blkverify.c
index 2077d8a..c548923 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -313,6 +313,8 @@ static BlockDriver bdrv_blkverify = {
     .bdrv_aio_readv         = blkverify_aio_readv,
     .bdrv_aio_writev        = blkverify_aio_writev,
     .bdrv_aio_flush         = blkverify_aio_flush,
+
+    .bdrv_check_ext_snapshot = bdrv_forbid_ext_snapshot,
 };
 
 static void bdrv_blkverify_init(void)
diff --git a/blockdev.c b/blockdev.c
index 8aa66a9..5c16f1b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1131,6 +1131,11 @@ static void external_snapshot_prepare(BlkTransactionState *common,
         }
     }
 
+    if (!bdrv_check_ext_snapshot(state->old_bs)) {
+        error_set(errp, QERR_FEATURE_DISABLED, "snapshot");
+        return;
+    }
+
     flags = state->old_bs->open_flags;
 
     /* create new image w/backing file */
diff --git a/include/block/block.h b/include/block/block.h
index f808550..df19610 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -244,6 +244,13 @@ int bdrv_check(BlockDriverState *bs, BdrvCheckResult *res, BdrvCheckMode fix);
 
 int bdrv_amend_options(BlockDriverState *bs_new, QEMUOptionParameter *options);
 
+/* external snapshots */
+
+/* return true if external snapshot is allowed, false if not */
+bool bdrv_check_ext_snapshot(BlockDriverState *bs);
+/* helper used to forbid external snapshots like in blkverify */
+bool bdrv_forbid_ext_snapshot(BlockDriverState *bs);
+
 /* async block I/O */
 typedef void BlockDriverDirtyHandler(BlockDriverState *bs, int64_t sector,
                                      int sector_num);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 211087a..cb92355 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -67,6 +67,14 @@ typedef struct BdrvTrackedRequest {
 struct BlockDriver {
     const char *format_name;
     int instance_size;
+
+    /* if not defined external snapshots are allowed
+     * if return true external snapshots are allowed
+     * if return false external snapshots are not allowed
+     * future block filters will query their children to build the response
+     */
+    bool (*bdrv_check_ext_snapshot)(BlockDriverState *bs);
+
     int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
     int (*bdrv_probe_device)(const char *filename);
 
-- 
1.8.1.2

Re: [Qemu-devel] [PATCH V2] block: Add BlockDriver.bdrv_check_ext_snapshot.

[Jeff Cody]

On Thu, Sep 26, 2013 at 04:33:49PM +0200, Benoît Canet wrote:
> This field is used by blkverify to disable external snapshots creation.
> I will also be used by block filters like quorum to disable external snapshots
> creation.
> 
> Signed-off-by: Benoit Canet <benoit@irqsave.net>
> ---
>  block.c                   | 14 ++++++++++++++
>  block/blkverify.c         |  2 ++
>  blockdev.c                |  5 +++++
>  include/block/block.h     |  7 +++++++
>  include/block/block_int.h |  8 ++++++++
>  5 files changed, 36 insertions(+)
> 
> diff --git a/block.c b/block.c
> index 4833b37..4da6fd9 100644
> --- a/block.c
> +++ b/block.c
> @@ -4632,3 +4632,17 @@ int bdrv_amend_options(BlockDriverState *bs, QEMUOptionParameter *options)
>      }
>      return bs->drv->bdrv_amend_options(bs, options);
>  }
> +
> +bool bdrv_check_ext_snapshot(BlockDriverState *bs)
> +{
> +    /* external snashots are enabled by defaults */
> +    if (!bs->drv->bdrv_check_ext_snapshot) {
> +        return true;
> +    }
> +    return bs->drv->bdrv_check_ext_snapshot(bs);
> +}
> +
> +bool bdrv_forbid_ext_snapshot(BlockDriverState *bs)
> +{
> +    return false;
> +}

The only problem I have with this now, is that
"bdrv_forbid_ext_snapshot()" returns false, to indicate that "forbid
ext snapshot" is true.  Looking at the function above, I would come to
the opposite conclusion as to what it does.

I understand why - you want the function name assigned to
.bdrv_check_ext_snapshot to reflect the action, but then that causes
the boolean return to be misleading.  Maybe returning an enum would be
more natural?

I apologize if this seems too pedantic.  :)

Thanks,
Jeff
> diff --git a/block/blkverify.c b/block/blkverify.c
> index 2077d8a..c548923 100644
> --- a/block/blkverify.c
> +++ b/block/blkverify.c
> @@ -313,6 +313,8 @@ static BlockDriver bdrv_blkverify = {
>      .bdrv_aio_readv         = blkverify_aio_readv,
>      .bdrv_aio_writev        = blkverify_aio_writev,
>      .bdrv_aio_flush         = blkverify_aio_flush,
> +
> +    .bdrv_check_ext_snapshot = bdrv_forbid_ext_snapshot,
>  };
>  
>  static void bdrv_blkverify_init(void)
> diff --git a/blockdev.c b/blockdev.c
> index 8aa66a9..5c16f1b 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1131,6 +1131,11 @@ static void external_snapshot_prepare(BlkTransactionState *common,
>          }
>      }
>  
> +    if (!bdrv_check_ext_snapshot(state->old_bs)) {
> +        error_set(errp, QERR_FEATURE_DISABLED, "snapshot");
> +        return;
> +    }
> +
>      flags = state->old_bs->open_flags;
>  
>      /* create new image w/backing file */
> diff --git a/include/block/block.h b/include/block/block.h
> index f808550..df19610 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -244,6 +244,13 @@ int bdrv_check(BlockDriverState *bs, BdrvCheckResult *res, BdrvCheckMode fix);
>  
>  int bdrv_amend_options(BlockDriverState *bs_new, QEMUOptionParameter *options);
>  
> +/* external snapshots */
> +
> +/* return true if external snapshot is allowed, false if not */
> +bool bdrv_check_ext_snapshot(BlockDriverState *bs);
> +/* helper used to forbid external snapshots like in blkverify */
> +bool bdrv_forbid_ext_snapshot(BlockDriverState *bs);
> +
>  /* async block I/O */
>  typedef void BlockDriverDirtyHandler(BlockDriverState *bs, int64_t sector,
>                                       int sector_num);
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 211087a..cb92355 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -67,6 +67,14 @@ typedef struct BdrvTrackedRequest {
>  struct BlockDriver {
>      const char *format_name;
>      int instance_size;
> +
> +    /* if not defined external snapshots are allowed
> +     * if return true external snapshots are allowed
> +     * if return false external snapshots are not allowed
> +     * future block filters will query their children to build the response
> +     */
> +    bool (*bdrv_check_ext_snapshot)(BlockDriverState *bs);
> +
>      int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
>      int (*bdrv_probe_device)(const char *filename);
>  
> -- 
> 1.8.1.2
> 
> 

Re: [Qemu-devel] [PATCH V2] block: Add BlockDriver.bdrv_check_ext_snapshot.

[Kevin Wolf]

Am 26.09.2013 um 18:48 hat Jeff Cody geschrieben:
> On Thu, Sep 26, 2013 at 04:33:49PM +0200, Benoît Canet wrote:
> > This field is used by blkverify to disable external snapshots creation.
> > I will also be used by block filters like quorum to disable external snapshots
> > creation.
> > 
> > Signed-off-by: Benoit Canet <benoit@irqsave.net>
> > ---
> >  block.c                   | 14 ++++++++++++++
> >  block/blkverify.c         |  2 ++
> >  blockdev.c                |  5 +++++
> >  include/block/block.h     |  7 +++++++
> >  include/block/block_int.h |  8 ++++++++
> >  5 files changed, 36 insertions(+)
> > 
> > diff --git a/block.c b/block.c
> > index 4833b37..4da6fd9 100644
> > --- a/block.c
> > +++ b/block.c
> > @@ -4632,3 +4632,17 @@ int bdrv_amend_options(BlockDriverState *bs, QEMUOptionParameter *options)
> >      }
> >      return bs->drv->bdrv_amend_options(bs, options);
> >  }
> > +
> > +bool bdrv_check_ext_snapshot(BlockDriverState *bs)
> > +{
> > +    /* external snashots are enabled by defaults */
> > +    if (!bs->drv->bdrv_check_ext_snapshot) {
> > +        return true;
> > +    }
> > +    return bs->drv->bdrv_check_ext_snapshot(bs);
> > +}
> > +
> > +bool bdrv_forbid_ext_snapshot(BlockDriverState *bs)
> > +{
> > +    return false;
> > +}
> 
> The only problem I have with this now, is that
> "bdrv_forbid_ext_snapshot()" returns false, to indicate that "forbid
> ext snapshot" is true.  Looking at the function above, I would come to
> the opposite conclusion as to what it does.
> 
> I understand why - you want the function name assigned to
> .bdrv_check_ext_snapshot to reflect the action, but then that causes
> the boolean return to be misleading.  Maybe returning an enum would be
> more natural?
> 
> I apologize if this seems too pedantic.  :)

Perhaps rename the function to bdrv_check_ext_snapshot_forbidden() or
something like that?

Kevin