[qemu-xen staging-4.13] block/snapshot: Restrict set of snapshot nodes

[patchbot@xxxxxxx]

commit 7a8aa6c734bb1c2927ad0cc1d10bcacb53cf4ae3
Author:     Kevin Wolf <kwolf@xxxxxxxxxx>
AuthorDate: Tue Sep 17 12:26:23 2019 +0200
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Nov 4 08:06:36 2019 -0600

    block/snapshot: Restrict set of snapshot nodes
    
    Nodes involved in internal snapshots were those that were returned by
    bdrv_next(), inserted and not read-only. bdrv_next() in turn returns all
    nodes that are either the root node of a BlockBackend or monitor-owned
    nodes.
    
    With the typical -drive use, this worked well enough. However, in the
    typical -blockdev case, the user defines one node per option, making all
    nodes monitor-owned nodes. This includes protocol nodes etc. which often
    are not snapshottable, so "savevm" only returns an error.
    
    Change the conditions so that internal snapshot still include all nodes
    that have a BlockBackend attached (we definitely want to snapshot
    anything attached to a guest device and probably also the built-in NBD
    server; snapshotting block job BlockBackends is more of an accident, but
    a preexisting one), but other monitor-owned nodes are only included if
    they have no parents.
    
    This makes internal snapshots usable again with typical -blockdev
    configurations.
    
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx>
    Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
    Reviewed-by: Peter Krempa <pkrempa@xxxxxxxxxx>
    Tested-by: Peter Krempa <pkrempa@xxxxxxxxxx>
    (cherry picked from commit 05f4aced658a02b02d3e89a6c7a2281008fcf26c)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 block/snapshot.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index f2f48f926a..8081616ae9 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -31,6 +31,7 @@
 #include "qapi/qmp/qerror.h"
 #include "qapi/qmp/qstring.h"
 #include "qemu/option.h"
+#include "sysemu/block-backend.h"
 
 QemuOptsList internal_snapshot_opts = {
     .name = "snapshot",
@@ -384,6 +385,16 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState 
*bs,
     return ret;
 }
 
+static bool bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
+{
+    if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
+        return false;
+    }
+
+    /* Include all nodes that are either in use by a BlockBackend, or that
+     * aren't attached to any node, but owned by the monitor. */
+    return bdrv_has_blk(bs) || QLIST_EMPTY(&bs->parents);
+}
 
 /* Group operations. All block drivers are involved.
  * These functions will properly handle dataplane (take aio_context_acquire
@@ -399,7 +410,7 @@ bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
-        if (bdrv_is_inserted(bs) && !bdrv_is_read_only(bs)) {
+        if (bdrv_all_snapshots_includes_bs(bs)) {
             ok = bdrv_can_snapshot(bs);
         }
         aio_context_release(ctx);
@@ -426,8 +437,9 @@ int bdrv_all_delete_snapshot(const char *name, 
BlockDriverState **first_bad_bs,
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
-        if (bdrv_can_snapshot(bs) &&
-                bdrv_snapshot_find(bs, snapshot, name) >= 0) {
+        if (bdrv_all_snapshots_includes_bs(bs) &&
+            bdrv_snapshot_find(bs, snapshot, name) >= 0)
+        {
             ret = bdrv_snapshot_delete(bs, snapshot->id_str,
                                        snapshot->name, err);
         }
@@ -455,7 +467,7 @@ int bdrv_all_goto_snapshot(const char *name, 
BlockDriverState **first_bad_bs,
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
-        if (bdrv_can_snapshot(bs)) {
+        if (bdrv_all_snapshots_includes_bs(bs)) {
             ret = bdrv_snapshot_goto(bs, name, errp);
         }
         aio_context_release(ctx);
@@ -481,7 +493,7 @@ int bdrv_all_find_snapshot(const char *name, 
BlockDriverState **first_bad_bs)
         AioContext *ctx = bdrv_get_aio_context(bs);
 
         aio_context_acquire(ctx);
-        if (bdrv_can_snapshot(bs)) {
+        if (bdrv_all_snapshots_includes_bs(bs)) {
             err = bdrv_snapshot_find(bs, &sn, name);
         }
         aio_context_release(ctx);
@@ -512,7 +524,7 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
         if (bs == vm_state_bs) {
             sn->vm_state_size = vm_state_size;
             err = bdrv_snapshot_create(bs, sn);
-        } else if (bdrv_can_snapshot(bs)) {
+        } else if (bdrv_all_snapshots_includes_bs(bs)) {
             sn->vm_state_size = 0;
             err = bdrv_snapshot_create(bs, sn);
         }
@@ -538,7 +550,7 @@ BlockDriverState *bdrv_all_find_vmstate_bs(void)
         bool found;
 
         aio_context_acquire(ctx);
-        found = bdrv_can_snapshot(bs);
+        found = bdrv_all_snapshots_includes_bs(bs) && bdrv_can_snapshot(bs);
         aio_context_release(ctx);
 
         if (found) {
--
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