block: add ability to specify list of blockdevs during snapshot

When running snapshot operations, there are various rules for which
blockdevs are included/excluded. While this provides reasonable default
behaviour, there are scenarios that are not well handled by the default
logic. Some of the conditions do not have a single correct answer.

Thus there needs to be a way for the mgmt app to provide an explicit
list of blockdevs to perform snapshots across. This can be achieved
by passing a list of node names that should be used.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210204124834.774401-5-berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 129 insertions, 43 deletions

diff --git a/block/snapshot.c b/block/snapshot.c
index 482e3fc7b7..220173deae 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -447,6 +447,41 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
     return ret;
 }
 
+
+static int bdrv_all_get_snapshot_devices(bool has_devices, strList *devices,
+                                         GList **all_bdrvs,
+                                         Error **errp)
+{
+    g_autoptr(GList) bdrvs = NULL;
+
+    if (has_devices) {
+        if (!devices) {
+            error_setg(errp, "At least one device is required for snapshot");
+            return -1;
+        }
+
+        while (devices) {
+            BlockDriverState *bs = bdrv_find_node(devices->value);
+            if (!bs) {
+                error_setg(errp, "No block device node '%s'", devices->value);
+                return -1;
+            }
+            bdrvs = g_list_append(bdrvs, bs);
+            devices = devices->next;
+        }
+    } else {
+        BlockDriverState *bs;
+        BdrvNextIterator it;
+        for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+            bdrvs = g_list_append(bdrvs, bs);
+        }
+    }
+
+    *all_bdrvs = g_steal_pointer(&bdrvs);
+    return 0;
+}
+
+
 static bool bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
 {
     if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
@@ -462,43 +497,59 @@ static bool bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
  * These functions will properly handle dataplane (take aio_context_acquire
  * when appropriate for appropriate block drivers) */
 
-bool bdrv_all_can_snapshot(Error **errp)
+bool bdrv_all_can_snapshot(bool has_devices, strList *devices,
+                           Error **errp)
 {
-    BlockDriverState *bs;
-    BdrvNextIterator it;
+    g_autoptr(GList) bdrvs = NULL;
+    GList *iterbdrvs;
 
-    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+    if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
+        return false;
+    }
+
+    iterbdrvs = bdrvs;
+    while (iterbdrvs) {
+        BlockDriverState *bs = iterbdrvs->data;
         AioContext *ctx = bdrv_get_aio_context(bs);
         bool ok = true;
 
         aio_context_acquire(ctx);
-        if (bdrv_all_snapshots_includes_bs(bs)) {
+        if (devices || bdrv_all_snapshots_includes_bs(bs)) {
             ok = bdrv_can_snapshot(bs);
         }
         aio_context_release(ctx);
         if (!ok) {
             error_setg(errp, "Device '%s' is writable but does not support "
                        "snapshots", bdrv_get_device_or_node_name(bs));
-            bdrv_next_cleanup(&it);
             return false;
         }
+
+        iterbdrvs = iterbdrvs->next;
     }
 
     return true;
 }
 
-int bdrv_all_delete_snapshot(const char *name, Error **errp)
+int bdrv_all_delete_snapshot(const char *name,
+                             bool has_devices, strList *devices,
+                             Error **errp)
 {
-    BlockDriverState *bs;
-    BdrvNextIterator it;
-    QEMUSnapshotInfo sn1, *snapshot = &sn1;
+    g_autoptr(GList) bdrvs = NULL;
+    GList *iterbdrvs;
+
+    if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
+        return -1;
+    }
 
-    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+    iterbdrvs = bdrvs;
+    while (iterbdrvs) {
+        BlockDriverState *bs = iterbdrvs->data;
         AioContext *ctx = bdrv_get_aio_context(bs);
+        QEMUSnapshotInfo sn1, *snapshot = &sn1;
         int ret = 0;
 
         aio_context_acquire(ctx);
-        if (bdrv_all_snapshots_includes_bs(bs) &&
+        if ((devices || bdrv_all_snapshots_includes_bs(bs)) &&
             bdrv_snapshot_find(bs, snapshot, name) >= 0)
         {
             ret = bdrv_snapshot_delete(bs, snapshot->id_str,
@@ -508,61 +559,80 @@ int bdrv_all_delete_snapshot(const char *name, Error **errp)
         if (ret < 0) {
             error_prepend(errp, "Could not delete snapshot '%s' on '%s': ",
                           name, bdrv_get_device_or_node_name(bs));
-            bdrv_next_cleanup(&it);
             return -1;
         }
+
+        iterbdrvs = iterbdrvs->next;
     }
 
     return 0;
 }
 
 
-int bdrv_all_goto_snapshot(const char *name, Error **errp)
+int bdrv_all_goto_snapshot(const char *name,
+                           bool has_devices, strList *devices,
+                           Error **errp)
 {
-    BlockDriverState *bs;
-    BdrvNextIterator it;
+    g_autoptr(GList) bdrvs = NULL;
+    GList *iterbdrvs;
 
-    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+    if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
+        return -1;
+    }
+
+    iterbdrvs = bdrvs;
+    while (iterbdrvs) {
+        BlockDriverState *bs = iterbdrvs->data;
         AioContext *ctx = bdrv_get_aio_context(bs);
         int ret = 0;
 
         aio_context_acquire(ctx);
-        if (bdrv_all_snapshots_includes_bs(bs)) {
+        if (devices || bdrv_all_snapshots_includes_bs(bs)) {
             ret = bdrv_snapshot_goto(bs, name, errp);
         }
         aio_context_release(ctx);
         if (ret < 0) {
             error_prepend(errp, "Could not load snapshot '%s' on '%s': ",
                           name, bdrv_get_device_or_node_name(bs));
-            bdrv_next_cleanup(&it);
             return -1;
         }
+
+        iterbdrvs = iterbdrvs->next;
     }
 
     return 0;
 }
 
-int bdrv_all_find_snapshot(const char *name, Error **errp)
+int bdrv_all_find_snapshot(const char *name,
+                           bool has_devices, strList *devices,
+                           Error **errp)
 {
-    QEMUSnapshotInfo sn;
-    BlockDriverState *bs;
-    BdrvNextIterator it;
+    g_autoptr(GList) bdrvs = NULL;
+    GList *iterbdrvs;
+
+    if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
+        return -1;
+    }
 
-    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+    iterbdrvs = bdrvs;
+    while (iterbdrvs) {
+        BlockDriverState *bs = iterbdrvs->data;
         AioContext *ctx = bdrv_get_aio_context(bs);
+        QEMUSnapshotInfo sn;
         int ret = 0;
 
         aio_context_acquire(ctx);
-        if (bdrv_all_snapshots_includes_bs(bs)) {
+        if (devices || bdrv_all_snapshots_includes_bs(bs)) {
             ret = bdrv_snapshot_find(bs, &sn, name);
         }
         aio_context_release(ctx);
         if (ret < 0) {
             error_setg(errp, "Could not find snapshot '%s' on '%s'",
                        name, bdrv_get_device_or_node_name(bs));
-            bdrv_next_cleanup(&it);
             return -1;
         }
+
+        iterbdrvs = iterbdrvs->next;
     }
 
     return 0;
@@ -571,12 +641,19 @@ int bdrv_all_find_snapshot(const char *name, Error **errp)
 int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
                              BlockDriverState *vm_state_bs,
                              uint64_t vm_state_size,
+                             bool has_devices, strList *devices,
                              Error **errp)
 {
-    BlockDriverState *bs;
-    BdrvNextIterator it;
+    g_autoptr(GList) bdrvs = NULL;
+    GList *iterbdrvs;
+
+    if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
+        return -1;
+    }
 
-    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+    iterbdrvs = bdrvs;
+    while (iterbdrvs) {
+        BlockDriverState *bs = iterbdrvs->data;
         AioContext *ctx = bdrv_get_aio_context(bs);
         int ret = 0;
 
@@ -584,7 +661,7 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
         if (bs == vm_state_bs) {
             sn->vm_state_size = vm_state_size;
             ret = bdrv_snapshot_create(bs, sn);
-        } else if (bdrv_all_snapshots_includes_bs(bs)) {
+        } else if (devices || bdrv_all_snapshots_includes_bs(bs)) {
             sn->vm_state_size = 0;
             ret = bdrv_snapshot_create(bs, sn);
         }
@@ -592,34 +669,43 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
         if (ret < 0) {
             error_setg(errp, "Could not create snapshot '%s' on '%s'",
                        sn->name, bdrv_get_device_or_node_name(bs));
-            bdrv_next_cleanup(&it);
             return -1;
         }
+
+        iterbdrvs = iterbdrvs->next;
     }
 
     return 0;
 }
 
-BlockDriverState *bdrv_all_find_vmstate_bs(Error **errp)
+BlockDriverState *bdrv_all_find_vmstate_bs(bool has_devices, strList *devices,
+                                           Error **errp)
 {
-    BlockDriverState *bs;
-    BdrvNextIterator it;
+    g_autoptr(GList) bdrvs = NULL;
+    GList *iterbdrvs;
 
-    for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
+    if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
+        return NULL;
+    }
+
+    iterbdrvs = bdrvs;
+    while (iterbdrvs) {
+        BlockDriverState *bs = iterbdrvs->data;
         AioContext *ctx = bdrv_get_aio_context(bs);
-        bool found;
+        bool found = false;
 
         aio_context_acquire(ctx);
-        found = bdrv_all_snapshots_includes_bs(bs) && bdrv_can_snapshot(bs);
+        found = (devices || bdrv_all_snapshots_includes_bs(bs)) &&
+            bdrv_can_snapshot(bs);
         aio_context_release(ctx);
 
         if (found) {
-            bdrv_next_cleanup(&it);
-            break;
+            return bs;
         }
+
+        iterbdrvs = iterbdrvs->next;
     }
-    if (!bs) {
-        error_setg(errp, "No block device supports snapshots");
-    }
-    return bs;
+
+    error_setg(errp, "No block device supports snapshots");
+    return NULL;
 }