Re: [Qemu-devel] [PATCH v2 3/4] block/dirty-bitmaps: add block_dirty_bitmap_check function

[Vladimir Sementsov-Ogievskiy]

23.02.2019 3:22, John Snow wrote:
> Instead of checking against busy, inconsistent, or read only directly,
> use a check function with permissions bits that let us streamline the
> checks without reproducing them in many places.
> 
> As a side effect, this adds consistency checks to all the QMP
> interfaces for bitmap manipulation.
> 
> Signed-off-by: John Snow <address@hidden>
> ---
>   block/dirty-bitmap.c           | 39 ++++++++++++++++++++-------
>   blockdev.c                     | 49 +++++++---------------------------
>   include/block/dirty-bitmap.h   | 13 ++++++++-
>   migration/block-dirty-bitmap.c | 12 +++------
>   nbd/server.c                   |  3 +--
>   5 files changed, 54 insertions(+), 62 deletions(-)
> 
> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
> index 4e8f931659..2e7fd81866 100644
> --- a/block/dirty-bitmap.c
> +++ b/block/dirty-bitmap.c
> @@ -174,7 +174,7 @@ bool bdrv_dirty_bitmap_has_successor(BdrvDirtyBitmap 
> *bitmap)
>       return bitmap->successor;
>   }
>   
> -bool bdrv_dirty_bitmap_busy(BdrvDirtyBitmap *bitmap) {
> +static bool bdrv_dirty_bitmap_busy(BdrvDirtyBitmap *bitmap) {
>       return bitmap->busy;
>   }
>   
> @@ -235,6 +235,33 @@ static bool bdrv_dirty_bitmap_recording(BdrvDirtyBitmap 
> *bitmap)
>                                    !bitmap->successor->disabled);
>   }
>   
> +int bdrv_dirty_bitmap_check(BdrvDirtyBitmap *bitmap, uint32_t flags,
> +                            Error **errp)
> +{
> +    if ((flags & BDRV_BITMAP_BUSY) && bdrv_dirty_bitmap_busy(bitmap)) {
> +        error_setg(errp, "Bitmap '%s' is currently in use by another"
> +                   " operation and cannot be used", bitmap->name);
> +        return -1;
> +    }
> +
> +    if ((flags & BDRV_BITMAP_RO) && bdrv_dirty_bitmap_readonly(bitmap)) {
> +        error_setg(errp, "Bitmap '%s' is readonly and cannot be modified",
> +                   bitmap->name);
> +        return -1;
> +    }
> +
> +    if ((flags & BDRV_BITMAP_INCONSISTENT) &&
> +        bdrv_dirty_bitmap_inconsistent(bitmap)) {
> +        error_setg(errp, "Bitmap '%s' is inconsistent and cannot be used",
> +                   bitmap->name);
> +        error_append_hint(errp, "Try block-dirty-bitmap-remove to delete "
> +                          "this bitmap from disk");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
>   /**
>    * Create a successor bitmap destined to replace this bitmap after an 
> operation.
>    * Requires that the bitmap is not user_locked and has no successor.
> @@ -792,15 +819,7 @@ void bdrv_merge_dirty_bitmap(BdrvDirtyBitmap *dest, 
> const BdrvDirtyBitmap *src,
>   
>       qemu_mutex_lock(dest->mutex);
>   
> -    if (bdrv_dirty_bitmap_busy(dest)) {
> -        error_setg(errp, "Bitmap '%s' is currently in use by another"
> -        " operation and cannot be modified", dest->name);
> -        goto out;
> -    }
> -
> -    if (bdrv_dirty_bitmap_readonly(dest)) {
> -        error_setg(errp, "Bitmap '%s' is readonly and cannot be modified",
> -                   dest->name);
> +    if (bdrv_dirty_bitmap_check(dest, BDRV_BITMAP_DEFAULT, errp)) {
>           goto out;
>       }
>   
> diff --git a/blockdev.c b/blockdev.c
> index cbce44877d..5d74479ba7 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -2007,11 +2007,7 @@ static void 
> block_dirty_bitmap_clear_prepare(BlkActionState *common,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(state->bitmap)) {
> -        error_setg(errp, "Cannot modify a bitmap in use by another 
> operation");
> -        return;
> -    } else if (bdrv_dirty_bitmap_readonly(state->bitmap)) {
> -        error_setg(errp, "Cannot clear a readonly bitmap");
> +    if (bdrv_dirty_bitmap_check(state->bitmap, BDRV_BITMAP_DEFAULT, errp)) {
>           return;
>       }
>   
> @@ -2056,10 +2052,7 @@ static void 
> block_dirty_bitmap_enable_prepare(BlkActionState *common,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(state->bitmap)) {
> -        error_setg(errp,
> -                   "Bitmap '%s' is currently in use by another operation"
> -                   " and cannot be enabled", action->name);
> +    if (bdrv_dirty_bitmap_check(state->bitmap, BDRV_BITMAP_ALLOW_RO, errp)) {
>           return;
>       }

hmm, preexisting, but seems a very bad idea to enable readonly bitmap.

>   
> @@ -2097,10 +2090,7 @@ static void 
> block_dirty_bitmap_disable_prepare(BlkActionState *common,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(state->bitmap)) {
> -        error_setg(errp,
> -                   "Bitmap '%s' is currently in use by another operation"
> -                   " and cannot be disabled", action->name);
> +    if (bdrv_dirty_bitmap_check(state->bitmap, BDRV_BITMAP_ALLOW_RO, errp)) {
>           return;
>       }

as well as disable too

>   
> @@ -2891,10 +2881,7 @@ void qmp_block_dirty_bitmap_remove(const char *node, 
> const char *name,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(bitmap)) {
> -        error_setg(errp,
> -                   "Bitmap '%s' is currently in use by another operation and"
> -                   " cannot be removed", name);
> +    if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_BUSY, errp)) {
>           return;
>       }

yes it's OK to remove inconsistent bitmap..

what about readonly? I don't see a problem with it, readonly just means that we 
didn't set INUSE
flag for bitmap, but if we are going to remove it, why not? But it most 
probably will fail,
as qcow2 image is most probably readonly too.

any way, it seems correct to chack only for _BUSY here.

>   
> @@ -2930,13 +2917,7 @@ void qmp_block_dirty_bitmap_clear(const char *node, 
> const char *name,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(bitmap)) {
> -        error_setg(errp,
> -                   "Bitmap '%s' is currently in use by another operation"
> -                   " and cannot be cleared", name);
> -        return;
> -    } else if (bdrv_dirty_bitmap_readonly(bitmap)) {
> -        error_setg(errp, "Bitmap '%s' is readonly and cannot be cleared", 
> name);
> +    if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_DEFAULT, errp)) {
>           return;
>       }
>   
> @@ -2954,10 +2935,7 @@ void qmp_block_dirty_bitmap_enable(const char *node, 
> const char *name,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(bitmap)) {
> -        error_setg(errp,
> -                   "Bitmap '%s' is currently in use by another operation"
> -                   " and cannot be enabled", name);
> +    if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_ALLOW_RO, errp)) {
>           return;
>       }
>   
> @@ -2975,10 +2953,7 @@ void qmp_block_dirty_bitmap_disable(const char *node, 
> const char *name,
>           return;
>       }
>   
> -    if (bdrv_dirty_bitmap_busy(bitmap)) {
> -        error_setg(errp,
> -                   "Bitmap '%s' is currently in use by another operation"
> -                   " and cannot be disabled", name);
> +    if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_ALLOW_RO, errp)) {
>           return;
>       }
>   
> @@ -3551,10 +3526,7 @@ static BlockJob *do_drive_backup(DriveBackup *backup, 
> JobTxn *txn,
>               bdrv_unref(target_bs);
>               goto out;
>           }
> -        if (bdrv_dirty_bitmap_busy(bmap)) {
> -            error_setg(errp,
> -                       "Bitmap '%s' is currently in use by another operation"
> -                       " and cannot be used for backup", backup->bitmap);
> +        if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_ALLOW_RO, errp)) {
>               goto out;
>           }
>       }
> @@ -3664,10 +3636,7 @@ BlockJob *do_blockdev_backup(BlockdevBackup *backup, 
> JobTxn *txn,
>               error_setg(errp, "Bitmap '%s' could not be found", 
> backup->bitmap);
>               goto out;
>           }
> -        if (bdrv_dirty_bitmap_busy(bmap)) {
> -            error_setg(errp,
> -                       "Bitmap '%s' is currently in use by another operation"
> -                       " and cannot be used for backup", backup->bitmap);
> +        if (bdrv_dirty_bitmap_check(bmap, BDRV_BITMAP_ALLOW_RO, errp)) {
>               goto out;
>           }
>       }

hmm, and doing backup on RO bitmap is questionable thing. On one hand - why 
not, we can.

But we will not be able to abdicate, as we can't modify bitmap.

So, it seems better to restrict it too. If use needs to do an incremental 
backup from
read-only image, not modifying a bitmap, he should either copy this bitmap 
(through
merge for example) to a not-persistent one, or he need a way to skip 
bitmap_abdicate.

> diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
> index b270773f7e..ee98b5014b 100644
> --- a/include/block/dirty-bitmap.h
> +++ b/include/block/dirty-bitmap.h
> @@ -5,6 +5,16 @@
>   #include "qapi/qapi-types-block-core.h"
>   #include "qemu/hbitmap.h"
>   
> +typedef enum BitmapCheckFlags {
> +    BDRV_BITMAP_BUSY = 1,
> +    BDRV_BITMAP_RO = 2,
> +    BDRV_BITMAP_INCONSISTENT = 4,
> +} BitmapCheckFlags;
> +
> +#define BDRV_BITMAP_DEFAULT (BDRV_BITMAP_BUSY | BDRV_BITMAP_RO |        \
> +                             BDRV_BITMAP_INCONSISTENT)
> +#define BDRV_BITMAP_ALLOW_RO (BDRV_BITMAP_BUSY | BDRV_BITMAP_INCONSISTENT)
> +
>   BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
>                                             uint32_t granularity,
>                                             const char *name,
> @@ -24,6 +34,8 @@ BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap(BlockDriverState 
> *bs,
>   void bdrv_dirty_bitmap_enable_successor(BdrvDirtyBitmap *bitmap);
>   BdrvDirtyBitmap *bdrv_find_dirty_bitmap(BlockDriverState *bs,
>                                           const char *name);
> +int bdrv_dirty_bitmap_check(BdrvDirtyBitmap *bitmap, uint32_t flags,
> +                            Error **errp);
>   void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap 
> *bitmap);
>   void bdrv_release_named_dirty_bitmaps(BlockDriverState *bs);
>   void bdrv_remove_persistent_dirty_bitmap(BlockDriverState *bs,
> @@ -93,7 +105,6 @@ bool bdrv_has_readonly_bitmaps(BlockDriverState *bs);
>   bool bdrv_dirty_bitmap_get_autoload(const BdrvDirtyBitmap *bitmap);
>   bool bdrv_dirty_bitmap_get_persistance(BdrvDirtyBitmap *bitmap);
>   bool bdrv_dirty_bitmap_inconsistent(BdrvDirtyBitmap *bitmap);
> -bool bdrv_dirty_bitmap_busy(BdrvDirtyBitmap *bitmap);
>   bool bdrv_has_changed_persistent_bitmaps(BlockDriverState *bs);
>   BdrvDirtyBitmap *bdrv_dirty_bitmap_next(BlockDriverState *bs,
>                                           BdrvDirtyBitmap *bitmap);
> diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
> index 7057fff242..0fcf897f32 100644
> --- a/migration/block-dirty-bitmap.c
> +++ b/migration/block-dirty-bitmap.c
> @@ -274,6 +274,7 @@ static int init_dirty_bitmap_migration(void)
>       BdrvDirtyBitmap *bitmap;
>       DirtyBitmapMigBitmapState *dbms;
>       BdrvNextIterator it;
> +    Error *local_err = NULL;
>   
>       dirty_bitmap_mig_state.bulk_completed = false;
>       dirty_bitmap_mig_state.prev_bs = NULL;
> @@ -301,15 +302,8 @@ static int init_dirty_bitmap_migration(void)
>                   goto fail;
>               }
>   
> -            if (bdrv_dirty_bitmap_busy(bitmap)) {
> -                error_report("Can't migrate a bitmap that is in use by 
> another operation: '%s'",
> -                             bdrv_dirty_bitmap_name(bitmap));
> -                goto fail;
> -            }
> -
> -            if (bdrv_dirty_bitmap_readonly(bitmap)) {
> -                error_report("Can't migrate read-only dirty bitmap: '%s",
> -                             bdrv_dirty_bitmap_name(bitmap));
> +            if (bdrv_dirty_bitmap_check(bitmap, BDRV_BITMAP_DEFAULT, 
> &local_err)) {
> +                error_report_err(local_err);
>                   goto fail;
>               }
>   
> diff --git a/nbd/server.c b/nbd/server.c
> index 02773e2836..9b87c7f243 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -1510,8 +1510,7 @@ NBDExport *nbd_export_new(BlockDriverState *bs, 
> uint64_t dev_offset,
>               goto fail;
>           }
>   
> -        if (bdrv_dirty_bitmap_busy(bm)) {
> -            error_setg(errp, "Bitmap '%s' is in use", bitmap);
> +        if (bdrv_dirty_bitmap_check(bm, BDRV_BITMAP_ALLOW_RO, errp)) {
>               goto fail;
>           }
>   
> 

and it is the only correct usage of ALLOW_RO, I think.

hmm, doesn't this mean that we should move to "int flags" in BdrvDirtyBitmap?

-- 
Best regards,
Vladimir