Re: [Qemu-devel] [RFC V3 6/7] block: Create authorizations mechanism for external snapshots.

["Benoît Canet" <benoit.canet@irqsave.net>]

Le Wednesday 04 Dec 2013 à 11:35:51 (+0800), Fam Zheng a écrit :
> On 2013年12月03日 21:26, Benoît Canet wrote:
> >---
> >  block.c                   | 64 +++++++++++++++++++++++++++++++++++++++++------
> >  block/blkverify.c         |  2 +-
> >  include/block/block.h     | 16 +++++++++---
> >  include/block/block_int.h |  9 ++++---
> >  4 files changed, 75 insertions(+), 16 deletions(-)
> >
> >diff --git a/block.c b/block.c
> >index 8016ff2..0569cb2 100644
> >--- a/block.c
> >+++ b/block.c
> >@@ -4945,21 +4945,69 @@ int bdrv_amend_options(BlockDriverState *bs, QEMUOptionParameter *options)
> >      return bs->drv->bdrv_amend_options(bs, options);
> >  }
> >
> >-ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs)
> >+/* will be used to recurse on single child block filter until first format
> >+ * (single child block filter will store their child in bs->file)
> >+ */
> >+ExtSnapshotPerm bdrv_generic_check_ext_snapshot(BlockDriverState *bs,
> >+                                                BlockDriverState *candidate)
> >  {
> >-    if (bs->drv->bdrv_check_ext_snapshot) {
> >-        return bs->drv->bdrv_check_ext_snapshot(bs);
> >+    if (!bs->drv) {
> >+        return EXT_SNAPSHOT_FORBIDDEN;
> >      }
> >
> >-    if (bs->file && bs->file->drv && bs->file->drv->bdrv_check_ext_snapshot) {
> >-        return bs->file->drv->bdrv_check_ext_snapshot(bs);
> >+    if (!bs->drv->authorizations[BS_CANT_SNAPSHOT]) {
> >+        if (bs == candidate) {
> >+             return EXT_SNAPSHOT_ALLOWED;
> >+        } else {
> >+             return EXT_SNAPSHOT_FORBIDDEN;
> >+        }
> >      }
> >
> >-    /* external snapshots are allowed by default */
> >-    return EXT_SNAPSHOT_ALLOWED;
> >+    if (!bs->drv->authorizations[BS_FILTER_PASS_DOWN]) {
> >+        return EXT_SNAPSHOT_FORBIDDEN;
> >+    }
> >+
> >+    if (!bs->file) {
> >+        return EXT_SNAPSHOT_FORBIDDEN;
> >+    }
> >+
> >+    return bdrv_recurse_check_ext_snapshot(bs->file, candidate);
> >  }
> >
> >-ExtSnapshotPerm bdrv_check_ext_snapshot_forbidden(BlockDriverState *bs)
> >+ExtSnapshotPerm bdrv_recurse_check_ext_snapshot(BlockDriverState *bs,
> >+                                                BlockDriverState *candidate)
> >  {
> >+    if (bs->drv && bs->drv->bdrv_check_ext_snapshot) {
> >+        return bs->drv->bdrv_check_ext_snapshot(bs, candidate);
> >+    }
> >+
> >+    return bdrv_generic_check_ext_snapshot(bs, candidate);
> >+}
> >+
> >+/* This function check if the candidate bs has snapshots authorized by going
> >+ * down the forest of bs, skipping filters and stopping on the the first bses
> >+ * authorizing snapshots
> >+ */
> >+ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *candidate)
> >+{
> >+    BlockDriverState *bs;
> >+
> >+    /* walk down the bs forest recursively */
> >+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
> >+        ExtSnapshotPerm perm;
> >+
> >+        if (!bs->file) {
> >+            continue;
> >+        }
> >+
> >+        perm = bdrv_recurse_check_ext_snapshot(bs->file, candidate);
> >+
> >+        /* allowed in the right subtree -> stop here */
> >+        if (perm == EXT_SNAPSHOT_ALLOWED) {
> >+            return EXT_SNAPSHOT_ALLOWED;
> >+        }
> >+    }
> >+
> >+    /* external snapshots are forbidden by default */
> >      return EXT_SNAPSHOT_FORBIDDEN;
> >  }
> >diff --git a/block/blkverify.c b/block/blkverify.c
> >index e755e4e..b93017c 100644
> >--- a/block/blkverify.c
> >+++ b/block/blkverify.c
> >@@ -313,7 +313,7 @@ static BlockDriver bdrv_blkverify = {
> >      .bdrv_aio_writev        = blkverify_aio_writev,
> >      .bdrv_aio_flush         = blkverify_aio_flush,
> >
> >-    .bdrv_check_ext_snapshot = bdrv_check_ext_snapshot_forbidden,
> >+    .authorizations         = { true, false },
> >  };
> >
> >  static void bdrv_blkverify_init(void)
> >diff --git a/include/block/block.h b/include/block/block.h
> >index 26c48e7..73c59fe 100644
> >--- a/include/block/block.h
> >+++ b/include/block/block.h
> >@@ -280,16 +280,24 @@ int bdrv_amend_options(BlockDriverState *bs_new, QEMUOptionParameter *options);
> >  /* external snapshots */
> >
> >  typedef enum {
> >-    EXT_SNAPSHOT_ALLOWED,
> >      EXT_SNAPSHOT_FORBIDDEN,
> >+    EXT_SNAPSHOT_ALLOWED,
> >  } ExtSnapshotPerm;
> >
> >+typedef enum {
> >+    BS_CANT_SNAPSHOT,
> >+    BS_FILTER_PASS_DOWN,
> >+    BS_AUTHORIZATION_COUNT,
> >+} BsAuthorization;
> >+
> >  /* return EXT_SNAPSHOT_ALLOWED if external snapshot is allowed
> >   * return EXT_SNAPSHOT_FORBIDDEN if external snapshot is forbidden
> >   */
> >-ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *bs);
> >-/* helper used to forbid external snapshots like in blkverify */
> >-ExtSnapshotPerm bdrv_check_ext_snapshot_forbidden(BlockDriverState *bs);
> >+ExtSnapshotPerm bdrv_generic_check_ext_snapshot(BlockDriverState *bs,
> >+                                                BlockDriverState *candidate);
> >+ExtSnapshotPerm bdrv_recurse_check_ext_snapshot(BlockDriverState *bs,
> >+                                                BlockDriverState *candidate);
> >+ExtSnapshotPerm bdrv_check_ext_snapshot(BlockDriverState *candidate);
> >
> >  /* async block I/O */
> >  typedef void BlockDriverDirtyHandler(BlockDriverState *bs, int64_t sector,
> >diff --git a/include/block/block_int.h b/include/block/block_int.h
> >index 9e789d2..d9704f2 100644
> >--- a/include/block/block_int.h
> >+++ b/include/block/block_int.h
> >@@ -69,10 +69,13 @@ struct BlockDriver {
> >      const char *format_name;
> >      int instance_size;
> >
> >-    /* if not defined external snapshots are allowed
> >-     * future block filters will query their children to build the response
> >+    /* this table of boolean contains authorizations for the block operations */
> >+    bool authorizations[BS_AUTHORIZATION_COUNT];
> 
> OK, I see some overlap of work here with my image fleecing patch series:
> 
> http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg03694.html
> 
> The disadvantage of using a bool array is that it can't keep track
> of multiple points in code that want to forbid the same operation.
> So I think an array of int is better here.
> 
> And what do you think of my posted interface, does it works for you?

Your is in BlockDriverState mine is in BlockDriver so there are not compatible.
I think we need to get advice from other people.

Best regards

Benoît

> 
> Fam
> 
> >+    /* future complex block filters will implement the following to query their
> >+     * children to check if snapshoting is allowed on a bs of the graph
> >       */
> >-    ExtSnapshotPerm (*bdrv_check_ext_snapshot)(BlockDriverState *bs);
> >+    ExtSnapshotPerm (*bdrv_check_ext_snapshot)(BlockDriverState *bs,
> >+                                               BlockDriverState *candidate);
> >
> >      int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
> >      int (*bdrv_probe_device)(const char *filename);
> >
> 
>