Add 'blockdev-snapshot' command

The 'snapshot-node-name' parameter of blockdev-snapshot-sync allows setting the node name of the image that is going to be created.

Before creating the image, external_snapshot_prepare() checks that the name is not already being used. The check is however incomplete since it only considers existing node names, but node names must not clash with device IDs either because they share the same namespace.

If the user attempts to create a snapshot using the name of an existing device for the 'snapshot-node-name' parameter the operation will eventually fail, but only after the new image has been created.

This patch replaces bdrv_find_node() with bdrv_lookup_bs() to extend the check to existing device IDs, and thus detect possible name clashes before the new image is created.

Signed-off-by Alberto Garcia <[email protected]>

---
 blockdev.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

One of the limitations of the 'blockdev-snapshot-sync' command is that it does not allow passing BlockdevOptions to the newly created snapshots, so they are always opened using the default values.

Extending the command to allow passing options is not a practical solution because there is overlap between those options and some of the existing parameters of the command.

This patch introduces a new 'blockdev-snapshot' command with a simpler
interface: it just takes two references to existing block devices that will be used as the source and target for the snapshot.

Since the main difference between the two commands is that one of them creates and opens the target image, while the other uses an already opened one, the bulk of the implementation is shared.

Signed-off-by Alberto Garcia <[email protected]>

Cc Eric Blake <[email protected]>

Reviewed-by Max Reitz <[email protected]>

---
 blockdev.c           | 165 ++++++++++++++++++++++++++++++++-------------------
 qapi-schema.json     |   2 +
 qapi/block-core.json |  28 +++++++++
 qmp-commands.hx      |  38 ++++++++++++
 4 files changed, 172 insertions(+), 61 deletions(-)

blockdev.c +0 -0

index 12741a0..b5470c9 100644

blockdev.c +0 -0

@@ -1521,58 +1533,48 @@ typedef struct ExternalSnapshotState {

     }
 
     /* start processing */

blockdev.c +0 -6

-    state->old_bs = bdrv_lookup_bs(has_device ? device : NULL,
-                                   has_node_name ? node_name : NULL,
-                                   &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
-        return;

blockdev.c +10 -9

+    state->old_bs = bdrv_lookup_bs(device, node_name, errp);
+    if (!state->old_bs) {
         return;
     }

@@ -1602,35 +1604,70 @@ static void external_snapshot_prepare(BlkTransactionState *common,
         return;
     }
 
-    flags = state->old_bs->open_flags;
+    if (action->kind == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) {
+        BlockdevSnapshotSync *s = action->blockdev_snapshot_sync;
+        const char *format = s->has_format ? s->format : "qcow2";
+        enum NewImageMode mode;
+        const char *snapshot_node_name =
+            s->has_snapshot_node_name ? s->snapshot_node_name : NULL;
 
-    /* create new image w/backing file */
-    if (mode != NEW_IMAGE_MODE_EXISTING) {
-        bdrv_img_create(new_image_file, format,
-                        state->old_bs->filename,
-                        state->old_bs->drv->format_name,
-                        NULL, -1, flags, &local_err, false);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        if (node_name && !snapshot_node_name) {
+            error_setg(errp, "New snapshot node name missing");
             return;

blockdev.c +35 -6

+            return;
+        }
+
+        flags = state->old_bs->open_flags;
+
+        /* create new image w/backing file */
+        mode = s->has_mode ? s->mode : NEW_IMAGE_MODE_ABSOLUTE_PATHS;
+        if (mode != NEW_IMAGE_MODE_EXISTING) {
+            bdrv_img_create(new_image_file, format,
+                            state->old_bs->filename,
+                            state->old_bs->drv->format_name,
+                            NULL, -1, flags, &local_err, false);
+            if (local_err) {
+                error_propagate(errp, local_err);
+                return;
+            }
+        }
+
+        options = qdict_new();
+        if (s->has_snapshot_node_name) {
+            qdict_put(options, "node-name",
+                      qstring_from_str(snapshot_node_name));
+        }
+        qdict_put(options, "driver", qstring_from_str(format));
+
+        flags |= BDRV_O_NO_BACKING;
     }
-    qdict_put(options, "driver", qstring_from_str(format));
 
-    /* TODO Inherit bs->options or only take explicit options with an
-     * extended QMP command? */
     assert(state->new_bs == NULL);
-    ret = bdrv_open(&state->new_bs, new_image_file, NULL, options,
-                    flags | BDRV_O_NO_BACKING, &local_err);
+    ret = bdrv_open(&state->new_bs, new_image_file, snapshot_ref, options,
+                    flags, errp);
     /* We will manually add the backing_hd field to the bs later */
     if (ret != 0) {
-        error_propagate(errp, local_err);
+        return;
+    }
+
+    if (state->new_bs->blk != NULL) {
+        error_setg(errp, "The snapshot is already in use by %s",
+                   blk_name(state->new_bs->blk));
+        return;

blockdev.c +0 -0

 }
 

blockdev.c typedef struct ExternalSnapshotState { · line 1575

Quoted 3 lines

blockdev.c +0 -3

-    if (has_snapshot_node_name &&
-        bdrv_lookup_bs(snapshot_node_name, snapshot_node_name, NULL)) {
-        error_setg(errp, "New snapshot node name already in use");

There's a difference from v6 here...

blockdev.c static void external_snapshot_prepare(BlkTransactionState *common, · line 1621

Quoted 7 lines

blockdev.c +3 -4

-    options = qdict_new();
-    if (has_snapshot_node_name) {
-        qdict_put(options, "node-name",
-                  qstring_from_str(snapshot_node_name));
+        if (snapshot_node_name &&
+            bdrv_lookup_bs(snapshot_node_name, snapshot_node_name, NULL)) {
+            error_setg(errp, "New snapshot node name already in use");

...and here, but how to resolve the conflict resulting from the newly added patch 1 was obvious, so my R-b stands, of course.

blockdev.c static void external_snapshot_prepare(BlkTransactionState *common, · line 1671

Quoted 3 lines

blockdev.c +2 -0

+    if (state->new_bs->backing_hd != NULL) {
+        error_setg(errp, "The snapshot already has a backing image");
     }

It's here: In case Kevin's series is applied before this one (which I'm assuming since you were brave enough to base this series on my BB series), this needs to be s/backing_hd/backing/. I'm just saying this so you know you can keep my R-b then.

The 'snapshot-node-name' parameter of blockdev-snapshot-sync allows setting the node name of the image that is going to be created.

Before creating the image, external_snapshot_prepare() checks that the name is not already being used. The check is however incomplete since it only considers existing node names, but node names must not clash with device IDs either because they share the same namespace.

If the user attempts to create a snapshot using the name of an existing device for the 'snapshot-node-name' parameter the operation will eventually fail, but only after the new image has been created.

This patch replaces bdrv_find_node() with bdrv_lookup_bs() to extend the check to existing device IDs, and thus detect possible name clashes before the new image is created.

Signed-off-by Alberto Garcia <[email protected]>

---
 blockdev.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

blockdev.c +3 -2

index 4731843..0898d1f 100644
@@ -1570,8 +1570,9 @@ static void external_snapshot_prepare(BlkTransactionState *common,
         return;
     }
 
-    if (has_snapshot_node_name && bdrv_find_node(snapshot_node_name)) {
-        error_setg(errp, "New snapshot node name already existing");
+    if (has_snapshot_node_name &&
+        bdrv_lookup_bs(snapshot_node_name, snapshot_node_name, NULL)) {
+        error_setg(errp, "New snapshot node name already in use");
         return;
     }
 

Signature · 1 line

2.6.1

We will introduce the 'blockdev-snapshot' command that will require its own struct for the parameters, so we need to rename this one in order to avoid name clashes.

Signed-off-by Alberto Garcia <[email protected]>

Reviewed-by Eric Blake <[email protected]>

Reviewed-by Max Reitz <[email protected]>

Reviewed-by Kevin Wolf <[email protected]>

---
 blockdev.c           | 2 +-
 qapi-schema.json     | 2 +-
 qapi/block-core.json | 8 ++++----
 3 files changed, 6 insertions(+), 6 deletions(-)

blockdev.c +1 -1

index 0898d1f..12741a0 100644
@@ -1166,7 +1166,7 @@ void qmp_blockdev_snapshot_sync(bool has_device, const char *device,
                                 bool has_format, const char *format,
                                 bool has_mode, NewImageMode mode, Error **errp)
 {
-    BlockdevSnapshot snapshot = {
+    BlockdevSnapshotSync snapshot = {
         .has_device = has_device,
         .device = (char *) device,
         .has_node_name = has_node_name,

qapi-schema.json +1 -1

index a05794e..65701dc 100644
@@ -1534,7 +1534,7 @@
 ##
 { 'union': 'TransactionAction',
   'data': {
-       'blockdev-snapshot-sync': 'BlockdevSnapshot',
+       'blockdev-snapshot-sync': 'BlockdevSnapshotSync',
        'drive-backup': 'DriveBackup',
        'blockdev-backup': 'BlockdevBackup',
        'abort': 'Abort',

qapi/block-core.json +4 -4

index 5f12af7..6b5ac02 100644
@@ -682,7 +682,7 @@
   'data': [ 'existing', 'absolute-paths' ] }
 
 ##
-# @BlockdevSnapshot
+# @BlockdevSnapshotSync
 #
 # Either @device or @node-name must be set but not both.
 #

@@ -699,7 +699,7 @@
 # @mode: #optional whether and how QEMU should create a new image, default is
 #        'absolute-paths'.
 ##
-{ 'struct': 'BlockdevSnapshot',
+{ 'struct': 'BlockdevSnapshotSync',
   'data': { '*device': 'str', '*node-name': 'str',
             'snapshot-file': 'str', '*snapshot-node-name': 'str',
             '*format': 'str', '*mode': 'NewImageMode' } }

@@ -790,7 +790,7 @@
 #
 # Generates a synchronous snapshot of a block device.
 #
-# For the arguments, see the documentation of BlockdevSnapshot.
+# For the arguments, see the documentation of BlockdevSnapshotSync.
 #
 # Returns: nothing on success
 #          If @device is not a valid block device, DeviceNotFound

@@ -798,7 +798,7 @@
 # Since 0.14.0
 ##
 { 'command': 'blockdev-snapshot-sync',
-  'data': 'BlockdevSnapshot' }
+  'data': 'BlockdevSnapshotSync' }
 
 ##
 # @change-backing-file

Signature · 1 line

2.6.1

Passing an empty string allows opening an image but not its backing file. This was already described in the API documentation, only the implementation was missing.

This is useful for creating snapshots using images opened with blockdev-add, since they are not supposed to have a backing image before the operation.

Signed-off-by Alberto Garcia <[email protected]>

Reviewed-by Max Reitz <[email protected]>

Reviewed-by Eric Blake <[email protected]>

Reviewed-by Kevin Wolf <[email protected]>

---
 block.c | 7 +++++++
 1 file changed, 7 insertions(+)

block.c +7 -0

index c9e3c6c..31d1b6e 100644
@@ -1406,6 +1406,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename,
     BlockDriverState *file = NULL, *bs;
     BlockDriver *drv = NULL;
     const char *drvname;
+    const char *backing;
     Error *local_err = NULL;
     int snapshot_flags = 0;
 

@@ -1473,6 +1474,12 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename,
 
     assert(drvname || !(flags & BDRV_O_PROTOCOL));
 
+    backing = qdict_get_try_str(options, "backing");
+    if (backing && *backing == '\0') {
+        flags |= BDRV_O_NO_BACKING;
+        qdict_del(options, "backing");
+    }
+
     bs->open_flags = flags;
     bs->options = options;
     options = qdict_clone_shallow(options);

Signature · 1 line

2.6.1

Signed-off-by Alberto Garcia <[email protected]>

Reviewed-by Max Reitz <[email protected]>

---
 tests/qemu-iotests/085     | 102 ++++++++++++++++++++++++++++++++++++++++++---
 tests/qemu-iotests/085.out |  34 ++++++++++++++-
 2 files changed, 128 insertions(+), 8 deletions(-)

tests/qemu-iotests/085 +96 -6

index 56cd6f8..9484117 100755
@@ -7,6 +7,7 @@
 # snapshots are performed.
 #
 # Copyright (C) 2014 Red Hat, Inc.
+# Copyright (C) 2015 Igalia, S.L.
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by

@@ -34,17 +35,17 @@ status=1	# failure is the default!
 snapshot_virt0="snapshot-v0.qcow2"
 snapshot_virt1="snapshot-v1.qcow2"
 
-MAX_SNAPSHOTS=10
+SNAPSHOTS=10
 
 _cleanup()
 {
     _cleanup_qemu
-    for i in $(seq 1 ${MAX_SNAPSHOTS})
+    for i in $(seq 1 ${SNAPSHOTS})
     do
         rm -f "${TEST_DIR}/${i}-${snapshot_virt0}"
         rm -f "${TEST_DIR}/${i}-${snapshot_virt1}"
     done
-	_cleanup_test_img
+    rm -f "${TEST_IMG}.1" "${TEST_IMG}.2"
 
 }
 trap "_cleanup; exit \$status" 0 1 2 3 15

@@ -85,18 +86,50 @@ function create_group_snapshot()
     _send_qemu_cmd $h "${cmd}" "return"
 }
 
+# ${1}: unique identifier for the snapshot filename
+# ${2}: true: open backing images; false: don't open them (default)
+function add_snapshot_image()
+{
+    if [ "${2}" = "true" ]; then
+        extra_params=""
+    else
+        extra_params="'backing': '', "
+    fi
+    base_image="${TEST_DIR}/$((${1}-1))-${snapshot_virt0}"
+    snapshot_file="${TEST_DIR}/${1}-${snapshot_virt0}"
+    _make_test_img -b "${base_image}" "$size"
+    mv "${TEST_IMG}" "${snapshot_file}"
+    cmd="{ 'execute': 'blockdev-add', 'arguments':
+           { 'options':
+             { 'driver': 'qcow2', 'node-name': 'snap_"${1}"', "${extra_params}"
+               'file':
+               { 'driver': 'file', 'filename': '"${snapshot_file}"' } } } }"
+    _send_qemu_cmd $h "${cmd}" "return"
+}
+
+# ${1}: unique identifier for the snapshot filename
+# ${2}: expected response, defaults to 'return'
+function blockdev_snapshot()
+{
+    cmd="{ 'execute': 'blockdev-snapshot',
+                      'arguments': { 'node': 'virtio0',
+                                     'overlay':'snap_"${1}"' } }"
+    _send_qemu_cmd $h "${cmd}" "${2:-return}"
+}
+
 size=128M
 
 _make_test_img $size
-mv "${TEST_IMG}" "${TEST_IMG}.orig"
+mv "${TEST_IMG}" "${TEST_IMG}.1"
 _make_test_img $size
+mv "${TEST_IMG}" "${TEST_IMG}.2"
 
 echo
 echo === Running QEMU ===
 echo
 
 qemu_comm_method="qmp"
-_launch_qemu -drive file="${TEST_IMG}.orig",if=virtio -drive file="${TEST_IMG}",if=virtio
+_launch_qemu -drive file="${TEST_IMG}.1",if=virtio -drive file="${TEST_IMG}.2",if=virtio
 h=$QEMU_HANDLE
 
 echo

@@ -105,6 +138,8 @@ echo
 
 _send_qemu_cmd $h "{ 'execute': 'qmp_capabilities' }" "return"
 
+# Tests for the blockdev-snapshot-sync command
+
 echo
 echo === Create a single snapshot on virtio0 ===
 echo

@@ -132,11 +167,66 @@ echo
 echo === Create several transactional group snapshots ===
 echo
 
-for i in $(seq 2 ${MAX_SNAPSHOTS})
+for i in $(seq 2 ${SNAPSHOTS})
 do
     create_group_snapshot ${i}
 done
 
+# Tests for the blockdev-snapshot command
+
+echo
+echo === Create a couple of snapshots using blockdev-snapshot ===
+echo
+
+SNAPSHOTS=$((${SNAPSHOTS}+1))
+add_snapshot_image ${SNAPSHOTS}
+blockdev_snapshot ${SNAPSHOTS}
+
+SNAPSHOTS=$((${SNAPSHOTS}+1))
+add_snapshot_image ${SNAPSHOTS}
+blockdev_snapshot ${SNAPSHOTS}
+
+echo
+echo === Invalid command - snapshot node used as active layer ===
+echo
+
+blockdev_snapshot ${SNAPSHOTS} error
+
+_send_qemu_cmd $h "{ 'execute': 'blockdev-snapshot',
+                     'arguments': { 'node':'virtio0',
+                                    'overlay':'virtio0' }
+                   }" "error"
+
+_send_qemu_cmd $h "{ 'execute': 'blockdev-snapshot',
+                     'arguments': { 'node':'virtio0',
+                                    'overlay':'virtio1' }
+                   }" "error"
+
+echo
+echo === Invalid command - snapshot node used as backing hd ===
+echo
+
+blockdev_snapshot $((${SNAPSHOTS}-1)) error
+
+echo
+echo === Invalid command - snapshot node has a backing image ===
+echo
+
+SNAPSHOTS=$((${SNAPSHOTS}+1))
+add_snapshot_image ${SNAPSHOTS} true
+blockdev_snapshot ${SNAPSHOTS} error
+
+echo
+echo === Invalid command - The node does not exist ===
+echo
+
+blockdev_snapshot $((${SNAPSHOTS}+1)) error
+
+_send_qemu_cmd $h "{ 'execute': 'blockdev-snapshot',
+                     'arguments': { 'node':'nodevice',
+                                    'overlay':'snap_"${SNAPSHOTS}"' }
+                   }" "error"
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/085.out +32 -2

index a6cf19e..52292ea 100644
@@ -11,7 +11,7 @@ Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
 
 === Create a single snapshot on virtio0 ===
 
-Formatting 'TEST_DIR/1-snapshot-v0.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/t.qcow2.orig backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/1-snapshot-v0.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/t.qcow2.1 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
 {"return": {}}
 
 === Invalid command - missing device and nodename ===

@@ -26,7 +26,7 @@ Formatting 'TEST_DIR/1-snapshot-v0.qcow2', fmt=qcow2 size=134217728 backing_file
 === Create several transactional group snapshots ===
 
 Formatting 'TEST_DIR/2-snapshot-v0.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/1-snapshot-v0.qcow2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
-Formatting 'TEST_DIR/2-snapshot-v1.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/t.qcow2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
+Formatting 'TEST_DIR/2-snapshot-v1.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/t.qcow2.2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
 {"return": {}}
 Formatting 'TEST_DIR/3-snapshot-v0.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/2-snapshot-v0.qcow2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
 Formatting 'TEST_DIR/3-snapshot-v1.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/2-snapshot-v1.qcow2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16

@@ -52,4 +52,34 @@ Formatting 'TEST_DIR/9-snapshot-v1.qcow2', fmt=qcow2 size=134217728 backing_file
 Formatting 'TEST_DIR/10-snapshot-v0.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/9-snapshot-v0.qcow2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
 Formatting 'TEST_DIR/10-snapshot-v1.qcow2', fmt=qcow2 size=134217728 backing_file=TEST_DIR/9-snapshot-v1.qcow2 backing_fmt=qcow2 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
 {"return": {}}
+
+=== Create a couple of snapshots using blockdev-snapshot ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/10-snapshot-v0.IMGFMT
+{"return": {}}
+{"return": {}}
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/11-snapshot-v0.IMGFMT
+{"return": {}}
+{"return": {}}
+
+=== Invalid command - snapshot node used as active layer ===
+
+{"error": {"class": "GenericError", "desc": "The snapshot is already in use by virtio0"}}
+{"error": {"class": "GenericError", "desc": "The snapshot is already in use by virtio0"}}
+{"error": {"class": "GenericError", "desc": "The snapshot is already in use by virtio1"}}
+
+=== Invalid command - snapshot node used as backing hd ===
+
+{"error": {"class": "GenericError", "desc": "Node 'snap_11' is busy: node is used as backing hd of 'virtio0'"}}
+
+=== Invalid command - snapshot node has a backing image ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/12-snapshot-v0.IMGFMT
+{"return": {}}
+{"error": {"class": "GenericError", "desc": "The snapshot already has a backing image"}}
+
+=== Invalid command - The node does not exist ===
+
+{"error": {"class": "GenericError", "desc": "Cannot find device=snap_14 nor node_name=snap_14"}}
+{"error": {"class": "GenericError", "desc": "Cannot find device=nodevice nor node_name=nodevice"}}
 *** done

Signature · 1 line

2.6.1