[Qemu-devel] [RFC PATCH COLO v2 09/13] block: Parse "backing_reference" option to reference existing BDS

[Wen Congyang <wency@cn.fujitsu.com>]

Usage:
-drive file=xxx,id=Y, \
-drive file=xxxx,id=X,backing_reference.drive_id=Y,backing_reference.hidden-disk.*

It will create such backing chain:
               {virtio-blk dev 'Y'}                                      {virtio-blk dev 'X'}
                         |                                                          |
                         |                                                          |
                         v                                                          v

    [base] <- [mid] <- ( Y )  <----------------- (hidden target) <--------------- ( X )

                         v                              ^
                         v                              ^
                         v                              ^
                         v                              ^
                         >>>> drive-backup sync=none >>>>

X's backing file is hidden-disk, and hidden-disk's backing file is Y.
Disk Y may be opened or reopened in read-write mode, so A block backup
job is automatically created: source is Y and target is hidden-disk.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
---
 block.c                    | 145 ++++++++++++++++++++++++++++++++++++++++++++-
 include/block/block.h      |   1 +
 include/block/block_int.h  |   1 +
 tests/qemu-iotests/051     |  13 ++++
 tests/qemu-iotests/051.out |  13 ++++
 5 files changed, 170 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index b4d629e..bd7fa9c 100644
--- a/block.c
+++ b/block.c
@@ -1351,6 +1351,113 @@ free_exit:
     return ret;
 }
 
+static void backing_reference_completed(void *opaque, int ret)
+{
+    BlockDriverState *hidden_disk = opaque;
+
+    assert(!hidden_disk->backing_reference);
+}
+
+static int bdrv_open_backing_reference_file(BlockDriverState *bs,
+                                            QDict *options, Error **errp)
+{
+    const char *backing_name;
+    QDict *hidden_disk_options = NULL;
+    BlockDriverState *backing_hd, *hidden_disk;
+    BlockBackend *backing_blk;
+    Error *local_err = NULL;
+    int ret = 0;
+
+    backing_name = qdict_get_try_str(options, "drive_id");
+    if (!backing_name) {
+        error_setg(errp, "Backing reference needs option drive_id");
+        ret = -EINVAL;
+        goto free_exit;
+    }
+    qdict_del(options, "drive_id");
+
+    qdict_extract_subqdict(options, &hidden_disk_options, "hidden-disk.");
+    if (!qdict_size(hidden_disk_options)) {
+        error_setg(errp, "Backing reference needs option hidden-disk.*");
+        ret = -EINVAL;
+        goto free_exit;
+    }
+
+    if (qdict_size(options)) {
+        const QDictEntry *entry = qdict_first(options);
+        error_setg(errp, "Backing reference used by '%s' doesn't support "
+                   "the option '%s'", bdrv_get_device_name(bs), entry->key);
+        ret = -EINVAL;
+        goto free_exit;
+    }
+
+    backing_blk = blk_by_name(backing_name);
+    if (!backing_blk) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, backing_name);
+        ret = -ENOENT;
+        goto free_exit;
+    }
+
+    backing_hd = blk_bs(backing_blk);
+    /* Backing reference itself? */
+    if (backing_hd == bs || bdrv_find_overlay(backing_hd, bs)) {
+        error_setg(errp, "Backing reference itself");
+        ret = -EINVAL;
+        goto free_exit;
+    }
+
+    if (bdrv_op_is_blocked(backing_hd, BLOCK_OP_TYPE_BACKING_REFERENCE,
+                           errp)) {
+        ret = -EBUSY;
+        goto free_exit;
+    }
+
+    /* hidden-disk is bs's backing file */
+    ret = bdrv_open_backing_file(bs, hidden_disk_options, errp);
+    hidden_disk_options = NULL;
+    if (ret < 0) {
+        goto free_exit;
+    }
+
+    hidden_disk = bs->backing_hd;
+    if (!hidden_disk->drv || !hidden_disk->drv->supports_backing) {
+        ret = -EINVAL;
+        error_setg(errp, "Hidden disk's driver doesn't support backing files");
+        goto free_exit;
+    }
+
+    bdrv_set_backing_hd(hidden_disk, backing_hd);
+    bdrv_ref(backing_hd);
+
+    /*
+     * backing hd may be opened or reopened in read-write mode, so we
+     * should backup backing hd to hidden disk
+     */
+    bdrv_op_unblock(hidden_disk, BLOCK_OP_TYPE_BACKUP_TARGET,
+                    bs->backing_blocker);
+    bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_BACKUP_SOURCE,
+                    hidden_disk->backing_blocker);
+
+    bdrv_ref(hidden_disk);
+    backup_start(backing_hd, hidden_disk, 0, MIRROR_SYNC_MODE_NONE,
+                 BLOCKDEV_ON_ERROR_REPORT, BLOCKDEV_ON_ERROR_REPORT,
+                 backing_reference_completed, hidden_disk, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        bdrv_unref(hidden_disk);
+        /* FIXME, use which errno? */
+        ret = -EIO;
+        goto free_exit;
+    }
+
+    bs->backing_reference = true;
+
+free_exit:
+    QDECREF(hidden_disk_options);
+    QDECREF(options);
+    return ret;
+}
+
 /*
  * Opens a disk image whose options are given as BlockdevRef in another block
  * device's options.
@@ -1604,13 +1711,37 @@ int bdrv_open(BlockDriverState **pbs, const char *filename,
 
     /* If there is a backing file, use it */
     if ((flags & BDRV_O_NO_BACKING) == 0) {
-        QDict *backing_options;
+        QDict *backing_options, *backing_reference_options;
 
+        qdict_extract_subqdict(options, &backing_reference_options,
+                               "backing_reference.");
         qdict_extract_subqdict(options, &backing_options, "backing.");
-        ret = bdrv_open_backing_file(bs, backing_options, &local_err);
-        if (ret < 0) {
+
+        if (qdict_size(backing_reference_options) &&
+            qdict_size(backing_options)) {
+            error_setg(&local_err,
+                       "Option \"backing_reference.*\" and \"backing.*\""
+                       " cannot be used together");
+            ret = -EINVAL;
+            QDECREF(backing_reference_options);
+            QDECREF(backing_options);
             goto close_and_fail;
         }
+        if (qdict_size(backing_reference_options)) {
+            QDECREF(backing_options);
+            ret = bdrv_open_backing_reference_file(bs,
+                                                   backing_reference_options,
+                                                   &local_err);
+            if (ret) {
+                goto close_and_fail;
+            }
+        } else {
+            QDECREF(backing_reference_options);
+            ret = bdrv_open_backing_file(bs, backing_options, &local_err);
+            if (ret < 0) {
+                goto close_and_fail;
+            }
+        }
     }
 
     bdrv_refresh_filename(bs);
@@ -1941,6 +2072,14 @@ void bdrv_close(BlockDriverState *bs)
     if (bs->drv) {
         if (bs->backing_hd) {
             BlockDriverState *backing_hd = bs->backing_hd;
+            if (bs->backing_reference) {
+                assert(backing_hd->backing_hd);
+                if (backing_hd->backing_hd->job) {
+                    block_job_cancel(backing_hd->backing_hd->job);
+                }
+                bdrv_set_backing_hd(backing_hd, NULL);
+                bdrv_unref(backing_hd->backing_hd);
+            }
             bdrv_set_backing_hd(bs, NULL);
             bdrv_unref(backing_hd);
         }
diff --git a/include/block/block.h b/include/block/block.h
index 68f3b1a..7138e90 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -159,6 +159,7 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_RESIZE,
     BLOCK_OP_TYPE_STREAM,
     BLOCK_OP_TYPE_REPLACE,
+    BLOCK_OP_TYPE_BACKING_REFERENCE,
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 08dd8ba..624945d 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -375,6 +375,7 @@ struct BlockDriverState {
     QDict *full_open_options;
     char exact_filename[PATH_MAX];
 
+    bool backing_reference;
     BlockDriverState *backing_hd;
     BlockDriverState *file;
 
diff --git a/tests/qemu-iotests/051 b/tests/qemu-iotests/051
index 0360f37..fd67f40 100755
--- a/tests/qemu-iotests/051
+++ b/tests/qemu-iotests/051
@@ -116,6 +116,19 @@ run_qemu -drive file="$TEST_IMG",file.backing.driver=file,file.backing.filename=
 run_qemu -drive file="$TEST_IMG",file.backing.driver=qcow2,file.backing.file.filename="$TEST_IMG.orig"
 
 echo
+echo === Backing file reference ===
+echo
+
+run_qemu -drive file="$TEST_IMG",if=none,id=drive0 \
+    -drive file="$TEST_IMG",driver=qcow2,backing_reference.drive_id=drive0,backing_reference.hidden-disk.filename="$TEST_IMG.hidden"
+
+run_qemu -drive file="$TEST_IMG",if=none,id=drive0 \
+    -drive file="$TEST_IMG",driver=qcow2,backing_reference.drive_id=drive0,backing_reference.hidden-disk.filename="$TEST_IMG.hidden",backing.file.filename="$TEST_IMG.orig"
+
+run_qemu -drive file="$TEST_IMG",if=none,id=drive0 \
+    -drive file="$TEST_IMG",driver=qcow2,file.backing_reference.drive_id=drive0,file.backing_reference.hidden-disk.filename="$TEST_IMG.hidden",file.backing.file.filename="$TEST_IMG.orig"
+
+echo
 echo === Enable and disable lazy refcounting on the command line, plus some invalid values ===
 echo
 
diff --git a/tests/qemu-iotests/051.out b/tests/qemu-iotests/051.out
index 2890eac..cb8340b 100644
--- a/tests/qemu-iotests/051.out
+++ b/tests/qemu-iotests/051.out
@@ -75,6 +75,19 @@ Testing: -drive file=TEST_DIR/t.qcow2,file.backing.driver=qcow2,file.backing.fil
 QEMU_PROG: -drive file=TEST_DIR/t.qcow2,file.backing.driver=qcow2,file.backing.file.filename=TEST_DIR/t.qcow2.orig: Driver doesn't support backing files
 
 
+=== Backing file reference ===
+
+Testing: -drive file=TEST_DIR/t.qcow2,if=none,id=drive0 -drive file=TEST_DIR/t.qcow2,driver=qcow2,backing_reference.drive_id=drive0,backing_reference.hidden-disk.filename=TEST_DIR/t.qcow2.hidden
+QEMU X.Y.Z monitor - type 'help' for more information
+(qemu) q^[[K^[[Dqu^[[K^[[D^[[Dqui^[[K^[[D^[[D^[[Dquit^[[K
+
+Testing: -drive file=TEST_DIR/t.qcow2,if=none,id=drive0 -drive file=TEST_DIR/t.qcow2,driver=qcow2,backing_reference.drive_id=drive0,backing_reference.hidden-disk.filename=TEST_DIR/t.qcow2.hidden,backing.file.filename=TEST_DIR/t.qcow2.orig
+QEMU_PROG: -drive file=TEST_DIR/t.qcow2,driver=qcow2,backing=drive0,backing.file.filename=TEST_DIR/t.qcow2.orig: Option "backing_reference.*" and "backing.*" cannot be used together
+
+Testing: -drive file=TEST_DIR/t.qcow2,if=none,id=drive0 -drive file=TEST_DIR/t.qcow2,driver=qcow2,file.backing_reference.drive_id=drive0,file.backing_reference.hidden-disk.filename=TEST_DIR/t.qcow2.hidden,file.backing.file.filename=TEST_DIR/t.qcow2.orig
+QEMU_PROG: -drive file=TEST_DIR/t.qcow2,driver=qcow2,file.backing=drive0,file.backing.file.filename=TEST_DIR/t.qcow2.orig: Option "backing_reference.*" and "backing.*" cannot be used together
+
+
 === Enable and disable lazy refcounting on the command line, plus some invalid values ===
 
 Testing: -drive file=TEST_DIR/t.qcow2,format=qcow2,lazy-refcounts=on
-- 
2.1.0