[Qemu-devel] [PATCH V4 0/4] Implement sync modes for drive-backup.

[Qemu-devel] [PATCH V4 0/4] Implement sync modes for drive-backup.

[Ian Main]

This patch adds sync modes on top of the work that Stefan Hajnoczi has done.

These patches apply on kevin/block with 
'[PATCH] block: add drive_backup HMP command' also applied.

Hopefully all is in order as this is my first QEMU patch.  Many thanks to 
Stephan and Fam Zheng for their help.

V2:

- No longer poll, instead use qemu_coroutine_yield().
- Use bdrv_co_is_allocated().
- Much better SYNC_MODE_NONE test.

V3:

- A few style fixes.
- Better commit message explaining how TOP and NONE operate.
- Verified using checkpatch.pl.

V4:

- Add patch to use the source as a backing hd during backup.
- Add patch to default sync mode none to qcow2.

Ian Main (4):
  Implement sync modes for drive-backup.
  Add tests for sync modes 'TOP' and 'NONE'
  Add backing drive while performing backup.
  Change default to qcow2 for sync mode none.

 block/backup.c                | 104 ++++++++++++++++++++++++++++++------------
 blockdev.c                    |  27 +++++++----
 include/block/block_int.h     |   4 +-
 qapi-schema.json              |   4 ++
 qmp-commands.hx               |   1 +
 tests/qemu-iotests/055        |  67 +++++++++++++++++++++++++--
 tests/qemu-iotests/055.out    |   4 +-
 tests/qemu-iotests/group      |   2 +-
 tests/qemu-iotests/iotests.py |   5 ++
 9 files changed, 171 insertions(+), 47 deletions(-)

-- 
1.8.1.4

[Qemu-devel] [PATCH V4 1/4] Implement sync modes for drive-backup.

[Ian Main]

This patch adds sync-modes to the drive-backup interface and
implements the FULL, NONE and TOP modes of synchronization.

FULL performs as before copying the entire contents of the drive
while preserving the point-in-time using CoW.
NONE only copies new writes to the target drive.
TOP copies changes to the topmost drive image and preserves the
point-in-time using CoW.

For sync mode TOP are creating a new target image using the same backing
file as the original disk image.  Then any new data that has been laid
on top of it since creation is copied in the main backup_run() loop.
There is an extra check in the 'TOP' case so that we don't bother to copy
all the data of the backing file as it already exists in the target.
This is where the bdrv_co_is_allocated() is used to determine if the
data exists in the topmost layer or below.

Also any new data being written is intercepted via the write_notifier
hook which ends up calling backup_do_cow() to copy old data out before
it gets overwritten.

For mode 'NONE' we create the new target image and only copy in the
original data from the disk image starting from the time the call was
made.  This preserves the point in time data by only copying the parts
that are *going to change* to the target image.  This way we can
reconstruct the final image by checking to see if the given block exists
in the new target image first, and if it does not, you can get it from
the original image.  This is basically an optimization allowing you to
do point-in-time snapshots with low overhead vs the 'FULL' version.

Since there is no old data to copy out the loop in backup_run() for the
NONE case just calls qemu_coroutine_yield() which only wakes up after
an event (usually cancel in this case).  The rest is handled by the
before_write notifier which again calls backup_do_cow() to write out
the old data so it can be preserved.

Signed-off-by: Ian Main <imain@redhat.com>
---
 block/backup.c            | 91 +++++++++++++++++++++++++++++++----------------
 blockdev.c                | 25 ++++++++-----
 include/block/block_int.h |  4 ++-
 qapi-schema.json          |  4 +++
 qmp-commands.hx           |  1 +
 5 files changed, 86 insertions(+), 39 deletions(-)

diff --git a/block/backup.c b/block/backup.c
index 16105d4..68abd23 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -37,6 +37,7 @@ typedef struct CowRequest {
 typedef struct BackupBlockJob {
     BlockJob common;
     BlockDriverState *target;
+    MirrorSyncMode sync_mode;
     RateLimit limit;
     BlockdevOnError on_source_error;
     BlockdevOnError on_target_error;
@@ -247,40 +248,69 @@ static void coroutine_fn backup_run(void *opaque)
 
     bdrv_add_before_write_notifier(bs, &before_write);
 
-    for (; start < end; start++) {
-        bool error_is_read;
-
-        if (block_job_is_cancelled(&job->common)) {
-            break;
+    if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {
+        while (!block_job_is_cancelled(&job->common)) {
+            /* Yield until the job is cancelled.  We just let our before_write
+             * notify callback service CoW requests. */
+            job->common.busy = false;
+            qemu_coroutine_yield();
+            job->common.busy = true;
         }
+    } else {
+        /* Both FULL and TOP SYNC_MODE's require copying.. */
+        for (; start < end; start++) {
+            bool error_is_read;
 
-        /* we need to yield so that qemu_aio_flush() returns.
-         * (without, VM does not reboot)
-         */
-        if (job->common.speed) {
-            uint64_t delay_ns = ratelimit_calculate_delay(
-                &job->limit, job->sectors_read);
-            job->sectors_read = 0;
-            block_job_sleep_ns(&job->common, rt_clock, delay_ns);
-        } else {
-            block_job_sleep_ns(&job->common, rt_clock, 0);
-        }
+            if (block_job_is_cancelled(&job->common)) {
+                break;
+            }
 
-        if (block_job_is_cancelled(&job->common)) {
-            break;
-        }
+            /* we need to yield so that qemu_aio_flush() returns.
+             * (without, VM does not reboot)
+             */
+            if (job->common.speed) {
+                uint64_t delay_ns = ratelimit_calculate_delay(
+                        &job->limit, job->sectors_read);
+                job->sectors_read = 0;
+                block_job_sleep_ns(&job->common, rt_clock, delay_ns);
+            } else {
+                block_job_sleep_ns(&job->common, rt_clock, 0);
+            }
 
-        ret = backup_do_cow(bs, start * BACKUP_SECTORS_PER_CLUSTER,
-                            BACKUP_SECTORS_PER_CLUSTER, &error_is_read);
-        if (ret < 0) {
-            /* Depending on error action, fail now or retry cluster */
-            BlockErrorAction action =
-                backup_error_action(job, error_is_read, -ret);
-            if (action == BDRV_ACTION_REPORT) {
+            if (block_job_is_cancelled(&job->common)) {
                 break;
-            } else {
-                start--;
-                continue;
+            }
+
+            if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {
+                int n, alloced;
+
+                /* Check to see if these blocks are already in the
+                 * backing file. */
+
+                alloced =
+                    bdrv_co_is_allocated(bs, start * BACKUP_SECTORS_PER_CLUSTER,
+                                         BACKUP_SECTORS_PER_CLUSTER, &n);
+                /* The above call returns true if the given sector is in the
+                 * topmost image.  If that is the case then we must copy it as
+                 * it has been modified from the original backing file.
+                 * Otherwise we skip it. */
+                if (alloced == 0) {
+                    continue;
+                }
+            }
+            /* FULL sync mode we copy the whole drive. */
+            ret = backup_do_cow(bs, start * BACKUP_SECTORS_PER_CLUSTER,
+                    BACKUP_SECTORS_PER_CLUSTER, &error_is_read);
+            if (ret < 0) {
+                /* Depending on error action, fail now or retry cluster */
+                BlockErrorAction action =
+                    backup_error_action(job, error_is_read, -ret);
+                if (action == BDRV_ACTION_REPORT) {
+                    break;
+                } else {
+                    start--;
+                    continue;
+                }
             }
         }
     }
@@ -300,7 +330,7 @@ static void coroutine_fn backup_run(void *opaque)
 }
 
 void backup_start(BlockDriverState *bs, BlockDriverState *target,
-                  int64_t speed,
+                  int64_t speed, MirrorSyncMode sync_mode,
                   BlockdevOnError on_source_error,
                   BlockdevOnError on_target_error,
                   BlockDriverCompletionFunc *cb, void *opaque,
@@ -335,6 +365,7 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
     job->on_source_error = on_source_error;
     job->on_target_error = on_target_error;
     job->target = target;
+    job->sync_mode = sync_mode;
     job->common.len = len;
     job->common.co = qemu_coroutine_create(backup_run);
     qemu_coroutine_enter(job->common.co, job);
diff --git a/blockdev.c b/blockdev.c
index c5abd65..000dea6 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1430,17 +1430,13 @@ void qmp_drive_backup(const char *device, const char *target,
                       Error **errp)
 {
     BlockDriverState *bs;
-    BlockDriverState *target_bs;
+    BlockDriverState *target_bs, *source;
     BlockDriver *drv = NULL;
     Error *local_err = NULL;
     int flags;
     int64_t size;
     int ret;
 
-    if (sync != MIRROR_SYNC_MODE_FULL) {
-        error_setg(errp, "only sync mode 'full' is currently supported");
-        return;
-    }
     if (!has_speed) {
         speed = 0;
     }
@@ -1483,6 +1479,13 @@ void qmp_drive_backup(const char *device, const char *target,
 
     flags = bs->open_flags | BDRV_O_RDWR;
 
+    /* See if we have a backing HD we can use to create our new image
+     * on top of. */
+    source = bs->backing_hd;
+    if (!source && sync == MIRROR_SYNC_MODE_TOP) {
+        sync = MIRROR_SYNC_MODE_FULL;
+    }
+
     size = bdrv_getlength(bs);
     if (size < 0) {
         error_setg_errno(errp, -size, "bdrv_getlength failed");
@@ -1491,8 +1494,14 @@ void qmp_drive_backup(const char *device, const char *target,
 
     if (mode != NEW_IMAGE_MODE_EXISTING) {
         assert(format && drv);
-        bdrv_img_create(target, format,
-                        NULL, NULL, NULL, size, flags, &local_err, false);
+        if (sync == MIRROR_SYNC_MODE_TOP) {
+            bdrv_img_create(target, format, source->filename,
+                            source->drv->format_name, NULL,
+                            size, flags, &local_err, false);
+        } else {
+            bdrv_img_create(target, format, NULL, NULL, NULL,
+                            size, flags, &local_err, false);
+        }
     }
 
     if (error_is_set(&local_err)) {
@@ -1508,7 +1517,7 @@ void qmp_drive_backup(const char *device, const char *target,
         return;
     }
 
-    backup_start(bs, target_bs, speed, on_source_error, on_target_error,
+    backup_start(bs, target_bs, speed, sync, on_source_error, on_target_error,
                  block_job_cb, bs, &local_err);
     if (local_err != NULL) {
         bdrv_delete(target_bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index c6ac871..e45f2a0 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -404,6 +404,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
  * @bs: Block device to operate on.
  * @target: Block device to write to.
  * @speed: The maximum speed, in bytes per second, or 0 for unlimited.
+ * @sync_mode: What parts of the disk image should be copied to the destination.
  * @on_source_error: The action to take upon error reading from the source.
  * @on_target_error: The action to take upon error writing to the target.
  * @cb: Completion function for the job.
@@ -413,7 +414,8 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
  * until the job is cancelled or manually completed.
  */
 void backup_start(BlockDriverState *bs, BlockDriverState *target,
-                  int64_t speed, BlockdevOnError on_source_error,
+                  int64_t speed, MirrorSyncMode sync_mode,
+                  BlockdevOnError on_source_error,
                   BlockdevOnError on_target_error,
                   BlockDriverCompletionFunc *cb, void *opaque,
                   Error **errp);
diff --git a/qapi-schema.json b/qapi-schema.json
index cdd2d6b..b3f6c2a 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1807,6 +1807,10 @@
 # @format: #optional the format of the new destination, default is to
 #          probe if @mode is 'existing', else the format of the source
 #
+# @sync: what parts of the disk image should be copied to the destination
+#        (all the disk, only the sectors allocated in the topmost image, or
+#        only new I/O).
+#
 # @mode: #optional whether and how QEMU should create a new image, default is
 #        'absolute-paths'.
 #
diff --git a/qmp-commands.hx b/qmp-commands.hx
index e075df4..f3f6b3d 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -957,6 +957,7 @@ Arguments:
 
 Example:
 -> { "execute": "drive-backup", "arguments": { "device": "drive0",
+                                               "sync": "full",
                                                "target": "backup.img" } }
 <- { "return": {} }
 EQMP
-- 
1.8.1.4

[Qemu-devel] [PATCH V4 2/4] Add tests for sync modes 'TOP' and 'NONE'

[Ian Main]

This patch adds tests for sync modes top and none.

Signed-off-by: Ian Main <imain@redhat.com>
---
 tests/qemu-iotests/055        | 67 ++++++++++++++++++++++++++++++++++++++++---
 tests/qemu-iotests/055.out    |  4 +--
 tests/qemu-iotests/group      |  2 +-
 tests/qemu-iotests/iotests.py |  5 ++++
 4 files changed, 71 insertions(+), 7 deletions(-)

diff --git a/tests/qemu-iotests/055 b/tests/qemu-iotests/055
index c66f8db..06d1f77 100755
--- a/tests/qemu-iotests/055
+++ b/tests/qemu-iotests/055
@@ -23,8 +23,9 @@
 import time
 import os
 import iotests
-from iotests import qemu_img, qemu_io
+from iotests import qemu_img, qemu_io, create_image
 
+backing_img = os.path.join(iotests.test_dir, 'backing.img')
 test_img = os.path.join(iotests.test_dir, 'test.img')
 target_img = os.path.join(iotests.test_dir, 'target.img')
 
@@ -34,7 +35,7 @@ class TestSingleDrive(iotests.QMPTestCase):
     def setUp(self):
         # Write data to the image so we can compare later
         qemu_img('create', '-f', iotests.imgfmt, test_img, str(TestSingleDrive.image_len))
-        qemu_io('-c', 'write -P0x5d 0 64k', test_img)
+        qemu_io('-c', 'write -P0x41 0 512', test_img)
         qemu_io('-c', 'write -P0xd5 1M 32k', test_img)
         qemu_io('-c', 'write -P0xdc 32M 124k', test_img)
         qemu_io('-c', 'write -P0xdc 67043328 64k', test_img)
@@ -60,6 +61,22 @@ class TestSingleDrive(iotests.QMPTestCase):
         event = self.cancel_and_wait()
         self.assert_qmp(event, 'data/type', 'backup')
 
+    def test_cancel_sync_none(self):
+        self.assert_no_active_block_jobs()
+
+        result = self.vm.qmp('drive-backup', device='drive0',
+                             sync='none', format='raw', target=target_img)
+        self.assert_qmp(result, 'return', {})
+        time.sleep(1)
+        self.vm.hmp_qemu_io('drive0', 'write -P0x5e 0 512')
+        self.vm.hmp_qemu_io('drive0', 'aio_flush')
+        time.sleep(1)
+        # Verify that the original contents exist in the target image.
+        self.assertEqual(-1, qemu_io('-c', 'read -P0x41 0 512', target_img).find("verification failed"))
+
+        event = self.cancel_and_wait()
+        self.assert_qmp(event, 'data/type', 'backup')
+
     def test_pause(self):
         self.assert_no_active_block_jobs()
 
@@ -102,6 +119,47 @@ class TestSingleDrive(iotests.QMPTestCase):
                              target=target_img, sync='full')
         self.assert_qmp(result, 'error/class', 'DeviceNotFound')
 
+class TestSyncModeTop(iotests.QMPTestCase):
+    image_len = 2 * 1024 * 1024 # MB
+
+    def setUp(self):
+        create_image(backing_img, TestSyncModeTop.image_len)
+        qemu_img('create', '-f', iotests.imgfmt, '-o', 'backing_file=%s' % backing_img, test_img)
+        qemu_io('-c', 'write -P0x5d 0 64k', test_img)
+        qemu_io('-c', 'write -P0xd5 1M 32k', test_img)
+        qemu_io('-c', 'write -P0xdc 32M 124k', test_img)
+        self.vm = iotests.VM().add_drive(test_img)
+        self.vm.launch()
+
+    def tearDown(self):
+        self.vm.shutdown()
+        os.remove(test_img)
+        os.remove(backing_img)
+        try:
+            os.remove(target_img)
+        except OSError:
+            pass
+
+    def test_complete_top(self):
+        self.assert_no_active_block_jobs()
+        result = self.vm.qmp('drive-backup', device='drive0', sync='top',
+                             target=target_img)
+        self.assert_qmp(result, 'return', {})
+
+        # Custom completed check as we are not copying all data.
+        completed = False
+        while not completed:
+            for event in self.vm.get_qmp_events(wait=True):
+                if event['event'] == 'BLOCK_JOB_COMPLETED':
+                    self.assert_qmp(event, 'data/device', 'drive0')
+                    self.assert_qmp_absent(event, 'data/error')
+                    completed = True
+
+        self.assert_no_active_block_jobs()
+        self.vm.shutdown()
+        self.assertTrue(iotests.compare_images(test_img, target_img),
+                        'target image does not match source after backup')
+
 class TestSetSpeed(iotests.QMPTestCase):
     image_len = 80 * 1024 * 1024 # MB
 
@@ -127,7 +185,8 @@ class TestSetSpeed(iotests.QMPTestCase):
         self.assert_qmp(result, 'return[0]/device', 'drive0')
         self.assert_qmp(result, 'return[0]/speed', 0)
 
-        result = self.vm.qmp('block-job-set-speed', device='drive0', speed=8 * 1024 * 1024)
+        result = self.vm.qmp('block-job-set-speed', device='drive0',
+                             speed=8 * 1024 * 1024)
         self.assert_qmp(result, 'return', {})
 
         # Ensure the speed we set was accepted
@@ -285,4 +344,4 @@ class TestSingleTransaction(iotests.QMPTestCase):
         self.assert_no_active_block_jobs()
 
 if __name__ == '__main__':
-    iotests.main(supported_fmts=['raw', 'qcow2'])
+    iotests.main(supported_fmts=['qcow2', 'qed'])
diff --git a/tests/qemu-iotests/055.out b/tests/qemu-iotests/055.out
index fa16b5c..96961ed 100644
--- a/tests/qemu-iotests/055.out
+++ b/tests/qemu-iotests/055.out
@@ -1,5 +1,5 @@
-.............
+...............
 ----------------------------------------------------------------------
-Ran 13 tests
+Ran 15 tests
 
 OK
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index fdc6ed1..d3c3f61 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -61,4 +61,4 @@
 052 rw auto backing
 053 rw auto
 054 rw auto
-055 rw auto
+055 rw auto backing
diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index b028a89..33ad0ec 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -95,6 +95,11 @@ class VM(object):
         self._num_drives += 1
         return self
 
+    def hmp_qemu_io(self, drive, cmd):
+        '''Write to a given drive using an HMP command'''
+        return self.qmp('human-monitor-command',
+                        command_line='qemu-io %s "%s"' % (drive, cmd))
+
     def add_fd(self, fd, fdset, opaque, opts=''):
         '''Pass a file descriptor to the VM'''
         options = ['fd=%d' % fd,
-- 
1.8.1.4

[Qemu-devel] [PATCH V4 3/4] Add backing drive while performing backup.

[Ian Main]

This patch adds the original source drive as a backing drive to our target
image so that the target image will appear complete during backup.  This
is especially useful for SYNC_MODE_NONE as it allows export via NBD to
have a complete point-in-time snapshot available for export.

Signed-off-by: Ian Main <imain@redhat.com>
---
 block/backup.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/block/backup.c b/block/backup.c
index 68abd23..e086e76 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -323,6 +323,10 @@ static void coroutine_fn backup_run(void *opaque)
 
     hbitmap_free(job->bitmap);
 
+    /* Set the target backing drive back to NULL before calling delete or
+     * it will also delete the underlying drive. */
+    target->backing_hd = NULL;
+
     bdrv_iostatus_disable(target);
     bdrv_delete(target);
 
@@ -362,6 +366,15 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
         return;
     }
 
+    /* Manually set the backing hd to be the backup source drive so
+     * that all reads done while we are backing up will be passed
+     * on to the original source drive.  This allows reading from the
+     * image while the backup is in progress, or in the case of
+     * SYNC_MODE_NONE allows a complete image to be present for export.
+     * Note that we do this for all modes including SYNC_MODE_TOP as
+     * even then it allows on-the-fly reading. */
+    target->backing_hd = bs;
+
     job->on_source_error = on_source_error;
     job->on_target_error = on_target_error;
     job->target = target;
-- 
1.8.1.4

[Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none.

[Ian Main]

qcow2 supports backing files so it makes sense to default to qcow2
for MIRROR_SYNC_MODE_NONE so that we can use the source as a backing
drive and export it via nbd.  Defaulting FULL and TOP to SYNC_MODE_NONE
breaks tests but that could be fixed if we wanted it.

Signed-off-by: Ian Main <imain@redhat.com>
---
 blockdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 000dea6..805b0e5 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1462,7 +1462,7 @@ void qmp_drive_backup(const char *device, const char *target,
     }
 
     if (!has_format) {
-        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
+        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2";
     }
     if (format) {
         drv = bdrv_find_format(format);
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH V4 3/4] Add backing drive while performing backup.

[Fam Zheng]

On Wed, 07/17 13:04, Ian Main wrote:
> This patch adds the original source drive as a backing drive to our target
> image so that the target image will appear complete during backup.  This
> is especially useful for SYNC_MODE_NONE as it allows export via NBD to
> have a complete point-in-time snapshot available for export.
> 
> Signed-off-by: Ian Main <imain@redhat.com>
> ---
>  block/backup.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/block/backup.c b/block/backup.c
> index 68abd23..e086e76 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -323,6 +323,10 @@ static void coroutine_fn backup_run(void *opaque)
>  
>      hbitmap_free(job->bitmap);
>  
> +    /* Set the target backing drive back to NULL before calling delete or
> +     * it will also delete the underlying drive. */
> +    target->backing_hd = NULL;
> +
>      bdrv_iostatus_disable(target);
>      bdrv_delete(target);
>  
> @@ -362,6 +366,15 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
>          return;
>      }
>  
> +    /* Manually set the backing hd to be the backup source drive so
> +     * that all reads done while we are backing up will be passed
> +     * on to the original source drive.  This allows reading from the
> +     * image while the backup is in progress, or in the case of
> +     * SYNC_MODE_NONE allows a complete image to be present for export.
> +     * Note that we do this for all modes including SYNC_MODE_TOP as
> +     * even then it allows on-the-fly reading. */
> +    target->backing_hd = bs;
> +

Also set target->backing_file and target->backing_format here? Paolo?

Thanks.

Fam

Re: [Qemu-devel] [PATCH V4 3/4] Add backing drive while performing backup.

[Paolo Bonzini]

Il 18/07/2013 08:39, Fam Zheng ha scritto:
> On Wed, 07/17 13:04, Ian Main wrote:
>> This patch adds the original source drive as a backing drive to our target
>> image so that the target image will appear complete during backup.  This
>> is especially useful for SYNC_MODE_NONE as it allows export via NBD to
>> have a complete point-in-time snapshot available for export.
>>
>> Signed-off-by: Ian Main <imain@redhat.com>
>> ---
>>  block/backup.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/block/backup.c b/block/backup.c
>> index 68abd23..e086e76 100644
>> --- a/block/backup.c
>> +++ b/block/backup.c
>> @@ -323,6 +323,10 @@ static void coroutine_fn backup_run(void *opaque)
>>  
>>      hbitmap_free(job->bitmap);
>>  
>> +    /* Set the target backing drive back to NULL before calling delete or
>> +     * it will also delete the underlying drive. */
>> +    target->backing_hd = NULL;
>> +
>>      bdrv_iostatus_disable(target);
>>      bdrv_delete(target);
>>  
>> @@ -362,6 +366,15 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
>>          return;
>>      }
>>  
>> +    /* Manually set the backing hd to be the backup source drive so
>> +     * that all reads done while we are backing up will be passed
>> +     * on to the original source drive.  This allows reading from the
>> +     * image while the backup is in progress, or in the case of
>> +     * SYNC_MODE_NONE allows a complete image to be present for export.
>> +     * Note that we do this for all modes including SYNC_MODE_TOP as
>> +     * even then it allows on-the-fly reading. */
>> +    target->backing_hd = bs;
>> +
> 
> Also set target->backing_file and target->backing_format here? Paolo?

I don't think so, it is temporary while the job runs so that the NBD
server can already return the actual data.

Paolo

Re: [Qemu-devel] [PATCH V4 1/4] Implement sync modes for drive-backup.

[Eric Blake]

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On 07/17/2013 02:04 PM, Ian Main wrote:
> This patch adds sync-modes to the drive-backup interface and
> implements the FULL, NONE and TOP modes of synchronization.
> 
> FULL performs as before copying the entire contents of the drive
> while preserving the point-in-time using CoW.
> NONE only copies new writes to the target drive.
> TOP copies changes to the topmost drive image and preserves the
> point-in-time using CoW.
> 

> +++ b/qapi-schema.json
> @@ -1807,6 +1807,10 @@
>  # @format: #optional the format of the new destination, default is to
>  #          probe if @mode is 'existing', else the format of the source
>  #
> +# @sync: what parts of the disk image should be copied to the destination
> +#        (all the disk, only the sectors allocated in the topmost image, or
> +#        only new I/O).
> +#
>  # @mode: #optional whether and how QEMU should create a new image, default is
>  #        'absolute-paths'.

This hunk looks bogus; the 'DriveBackup' type already documents @sync as
of commit b53169e, which makes me suspect this hunk got misapplied
during rebasing.

>  #
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index e075df4..f3f6b3d 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -957,6 +957,7 @@ Arguments:
>  
>  Example:
>  -> { "execute": "drive-backup", "arguments": { "device": "drive0",
> +                                               "sync": "full",
>                                                 "target": "backup.img" } }

Ouch - commit b53169e made 'sync' mandatory, but forgot to update the
example to match; perhaps this hunk ought to be applied independently?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none.

[Eric Blake]

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On 07/17/2013 02:04 PM, Ian Main wrote:
> qcow2 supports backing files so it makes sense to default to qcow2
> for MIRROR_SYNC_MODE_NONE so that we can use the source as a backing
> drive and export it via nbd.  Defaulting FULL and TOP to SYNC_MODE_NONE
> breaks tests but that could be fixed if we wanted it.
> 
> Signed-off-by: Ian Main <imain@redhat.com>
> ---
>  blockdev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 000dea6..805b0e5 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -1462,7 +1462,7 @@ void qmp_drive_backup(const char *device, const char *target,
>      }
>  
>      if (!has_format) {
> -        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
> +        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2";

Is this the right thing to do?  Or should we do:

if (!has_format) {
    if (mode == NEW_IMAGE_MODE_EXISTING) {
        format = NULL;
    } else {
        format = bs->drv->format_name ?: "qcow2";
    }
}

That is, I think we should default to doing a backup in the format given
by the original (what if the original is qed, which also supports
backing files), and only use qcow2 when there is no guidance whatsoever.

But in practice, I don't care - format probing is a security hole, so
libvirt should always be passing a format, at which point the entire
!has_format condition should be skipped when called by libvirt.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none.

[Eric Blake]

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On 07/18/2013 11:27 AM, Eric Blake wrote:

>>      if (!has_format) {
>> -        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
>> +        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2";
> 
> Is this the right thing to do?  Or should we do:
> 
> if (!has_format) {
>     if (mode == NEW_IMAGE_MODE_EXISTING) {
>         format = NULL;
>     } else {
>         format = bs->drv->format_name ?: "qcow2";
>     }
> }
> 
> That is, I think we should default to doing a backup in the format given
> by the original (what if the original is qed, which also supports
> backing files), and only use qcow2 when there is no guidance whatsoever.
> 
> But in practice, I don't care

Well, I _DO_ care about one thing - make sure that the qapi-schema.json
page accurately documents how this variable is defaulted for callers
that don't care about the implications of omitting a format.

Or we could simplify life by making 'format' mandatory for drive-backup;
it was optional for 'drive-mirror' due to incremental implementation,
but for 'drive-backup', we still have the opportunity to do things right
from the first release.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none.

[Ian Main]

On Thu, Jul 18, 2013 at 11:32:52AM -0600, Eric Blake wrote:
> On 07/18/2013 11:27 AM, Eric Blake wrote:
> 
> >>      if (!has_format) {
> >> -        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
> >> +        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2";
> > 
> > Is this the right thing to do?  Or should we do:
> > 
> > if (!has_format) {
> >     if (mode == NEW_IMAGE_MODE_EXISTING) {
> >         format = NULL;
> >     } else {
> >         format = bs->drv->format_name ?: "qcow2";
> >     }
> > }
> > 
> > That is, I think we should default to doing a backup in the format given
> > by the original (what if the original is qed, which also supports
> > backing files), and only use qcow2 when there is no guidance whatsoever.
> > 
> > But in practice, I don't care
> 
> Well, I _DO_ care about one thing - make sure that the qapi-schema.json
> page accurately documents how this variable is defaulted for callers
> that don't care about the implications of omitting a format.
> 
> Or we could simplify life by making 'format' mandatory for drive-backup;
> it was optional for 'drive-mirror' due to incremental implementation,
> but for 'drive-backup', we still have the opportunity to do things right
> from the first release.

Ah, I did make a doc change, I must have forgotten to add it.

I'm all for making format mandatory if that is ok with everyone.  Maybe
that is the best solution.

	Ian

Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none.

[Ian Main]

On Thu, Jul 18, 2013 at 11:27:21AM -0600, Eric Blake wrote:
> On 07/17/2013 02:04 PM, Ian Main wrote:
> > qcow2 supports backing files so it makes sense to default to qcow2
> > for MIRROR_SYNC_MODE_NONE so that we can use the source as a backing
> > drive and export it via nbd.  Defaulting FULL and TOP to SYNC_MODE_NONE
> > breaks tests but that could be fixed if we wanted it.
> > 
> > Signed-off-by: Ian Main <imain@redhat.com>
> > ---
> >  blockdev.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/blockdev.c b/blockdev.c
> > index 000dea6..805b0e5 100644
> > --- a/blockdev.c
> > +++ b/blockdev.c
> > @@ -1462,7 +1462,7 @@ void qmp_drive_backup(const char *device, const char *target,
> >      }
> >  
> >      if (!has_format) {
> > -        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
> > +        format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : "qcow2";
> 
> Is this the right thing to do?  Or should we do:
> 
> if (!has_format) {
>     if (mode == NEW_IMAGE_MODE_EXISTING) {
>         format = NULL;
>     } else {
>         format = bs->drv->format_name ?: "qcow2";
>     }
> }
> 
> That is, I think we should default to doing a backup in the format given
> by the original (what if the original is qed, which also supports
> backing files), and only use qcow2 when there is no guidance whatsoever.
> 
> But in practice, I don't care - format probing is a security hole, so
> libvirt should always be passing a format, at which point the entire
> !has_format condition should be skipped when called by libvirt.

Heh, actually that is basically what I have now, as with the doc change
I forgot to git add it.  Doh!  I'll repost.. I'm also not opposed to
format being non-optional.

	Ian

Re: [Qemu-devel] [PATCH V4 4/4] Change default to qcow2 for sync mode none.

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1166 bytes --]

On 07/18/2013 12:03 PM, Ian Main wrote:
>>
>> Or we could simplify life by making 'format' mandatory for drive-backup;
>> it was optional for 'drive-mirror' due to incremental implementation,
>> but for 'drive-backup', we still have the opportunity to do things right
>> from the first release.
> 
> Ah, I did make a doc change, I must have forgotten to add it.
> 
> I'm all for making format mandatory if that is ok with everyone.  Maybe
> that is the best solution.

We can always change our mind in 1.7 to make it optional if we change
our minds, but I'd definitely like to see patches that make 'format'
mandatory for DriveBackup for 1.6 - simpler all around.  Converting
mandatory to optional is discoverable via introspection; while
converting optional to mandatory is an API break.  And since we can
argue that optional formats is relatively risky, it's better to have our
initial release be conservative by requiring the field until (and
unless) someone comes up with a use case why leaving it unspecified
makes a difference.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH V4 1/4] Implement sync modes for drive-backup.

[Ian Main]

On Thu, Jul 18, 2013 at 11:19:43AM -0600, Eric Blake wrote:
> On 07/17/2013 02:04 PM, Ian Main wrote:
> > This patch adds sync-modes to the drive-backup interface and
> > implements the FULL, NONE and TOP modes of synchronization.
> > 
> > FULL performs as before copying the entire contents of the drive
> > while preserving the point-in-time using CoW.
> > NONE only copies new writes to the target drive.
> > TOP copies changes to the topmost drive image and preserves the
> > point-in-time using CoW.
> > 
> 
> > +++ b/qapi-schema.json
> > @@ -1807,6 +1807,10 @@
> >  # @format: #optional the format of the new destination, default is to
> >  #          probe if @mode is 'existing', else the format of the source
> >  #
> > +# @sync: what parts of the disk image should be copied to the destination
> > +#        (all the disk, only the sectors allocated in the topmost image, or
> > +#        only new I/O).
> > +#
> >  # @mode: #optional whether and how QEMU should create a new image, default is
> >  #        'absolute-paths'.
> 
> This hunk looks bogus; the 'DriveBackup' type already documents @sync as
> of commit b53169e, which makes me suspect this hunk got misapplied
> during rebasing.

Did you check that?  I know there was one bit of documentation missing
that I fixed here.  I also just did a clean rebase (git am) to
kevin/block and it all applied fine.
 
> >  #
> > diff --git a/qmp-commands.hx b/qmp-commands.hx
> > index e075df4..f3f6b3d 100644
> > --- a/qmp-commands.hx
> > +++ b/qmp-commands.hx
> > @@ -957,6 +957,7 @@ Arguments:
> >  
> >  Example:
> >  -> { "execute": "drive-backup", "arguments": { "device": "drive0",
> > +                                               "sync": "full",
> >                                                 "target": "backup.img" } }
> 
> Ouch - commit b53169e made 'sync' mandatory, but forgot to update the
> example to match; perhaps this hunk ought to be applied independently?

That's up to you guys, I can split it out if needed.

	Ian

Re: [Qemu-devel] [PATCH V4 1/4] Implement sync modes for drive-backup.

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 2433 bytes --]

On 07/18/2013 01:06 PM, Ian Main wrote:
> On Thu, Jul 18, 2013 at 11:19:43AM -0600, Eric Blake wrote:
>> On 07/17/2013 02:04 PM, Ian Main wrote:
>>> This patch adds sync-modes to the drive-backup interface and
>>> implements the FULL, NONE and TOP modes of synchronization.
>>>

>>> @@ -1807,6 +1807,10 @@
>>>  # @format: #optional the format of the new destination, default is to
>>>  #          probe if @mode is 'existing', else the format of the source
>>>  #
>>> +# @sync: what parts of the disk image should be copied to the destination
>>> +#        (all the disk, only the sectors allocated in the topmost image, or
>>> +#        only new I/O).
>>> +#
>>>  # @mode: #optional whether and how QEMU should create a new image, default is
>>>  #        'absolute-paths'.
>>
>> This hunk looks bogus; the 'DriveBackup' type already documents @sync as
>> of commit b53169e, which makes me suspect this hunk got misapplied
>> during rebasing.
> 
> Did you check that?  I know there was one bit of documentation missing
> that I fixed here.  I also just did a clean rebase (git am) to
> kevin/block and it all applied fine.

Yes, it _applied_ fine, because of git's insistence on applying hunks
regardless of line fuzzing.  It probably applied to 'drive-mirror',
since I see this context in the section for 'drive-mirror' when reading
the unpatched file at current qemu.git head:

> # @format: #optional the format of the new destination, default is to
> #          probe if @mode is 'existing', else the format of the source
> #
> # @mode: #optional whether and how QEMU should create a new image, default is
> #        'absolute-paths'.
> #

Hence, my argument that you DON'T want this hunk.

>>>  Example:
>>>  -> { "execute": "drive-backup", "arguments": { "device": "drive0",
>>> +                                               "sync": "full",
>>>                                                 "target": "backup.img" } }
>>
>> Ouch - commit b53169e made 'sync' mandatory, but forgot to update the
>> example to match; perhaps this hunk ought to be applied independently?
> 
> That's up to you guys, I can split it out if needed.

I don't care either way as long as it gets fixed before 1.6; it all
depends on how long the review of the rest of your series takes.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH V4 3/4] Add backing drive while performing backup.

[Fam Zheng]

On Thu, 07/18 15:13, Paolo Bonzini wrote:
> Il 18/07/2013 08:39, Fam Zheng ha scritto:
> > On Wed, 07/17 13:04, Ian Main wrote:
> >> This patch adds the original source drive as a backing drive to our target
> >> image so that the target image will appear complete during backup.  This
> >> is especially useful for SYNC_MODE_NONE as it allows export via NBD to
> >> have a complete point-in-time snapshot available for export.
> >>
> >> Signed-off-by: Ian Main <imain@redhat.com>
> >> ---
> >>  block/backup.c | 13 +++++++++++++
> >>  1 file changed, 13 insertions(+)
> >>
> >> diff --git a/block/backup.c b/block/backup.c
> >> index 68abd23..e086e76 100644
> >> --- a/block/backup.c
> >> +++ b/block/backup.c
> >> @@ -323,6 +323,10 @@ static void coroutine_fn backup_run(void *opaque)
> >>  
> >>      hbitmap_free(job->bitmap);
> >>  
> >> +    /* Set the target backing drive back to NULL before calling delete or
> >> +     * it will also delete the underlying drive. */
> >> +    target->backing_hd = NULL;
> >> +
> >>      bdrv_iostatus_disable(target);
> >>      bdrv_delete(target);
> >>  
> >> @@ -362,6 +366,15 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
> >>          return;
> >>      }
> >>  
> >> +    /* Manually set the backing hd to be the backup source drive so
> >> +     * that all reads done while we are backing up will be passed
> >> +     * on to the original source drive.  This allows reading from the
> >> +     * image while the backup is in progress, or in the case of
> >> +     * SYNC_MODE_NONE allows a complete image to be present for export.
> >> +     * Note that we do this for all modes including SYNC_MODE_TOP as
> >> +     * even then it allows on-the-fly reading. */
> >> +    target->backing_hd = bs;
> >> +
> > 
> > Also set target->backing_file and target->backing_format here? Paolo?
> 
> I don't think so, it is temporary while the job runs so that the NBD
> server can already return the actual data.

OK.

For NBD export, it's also going to have a name, to be used with
nbd_server_add. So should we call bdrv_set_in_use() here to protect
target from being used elsewhere?

-- 
Fam

Re: [Qemu-devel] [PATCH V4 3/4] Add backing drive while performing backup.

[Paolo Bonzini]

Il 19/07/2013 03:13, Fam Zheng ha scritto:
>>> > > Also set target->backing_file and target->backing_format here? Paolo?
>> > 
>> > I don't think so, it is temporary while the job runs so that the NBD
>> > server can already return the actual data.
> OK.
> 
> For NBD export, it's also going to have a name, to be used with
> nbd_server_add. So should we call bdrv_set_in_use() here to protect
> target from being used elsewhere?

I think it'd still be safe, but it's probably a good idea anyway.

Paolo

Re: [Qemu-devel] [PATCH V4 1/4] Implement sync modes for drive-backup.

[Ian Main]

On Thu, Jul 18, 2013 at 01:54:45PM -0600, Eric Blake wrote:
> On 07/18/2013 01:06 PM, Ian Main wrote:
> > On Thu, Jul 18, 2013 at 11:19:43AM -0600, Eric Blake wrote:
> >> On 07/17/2013 02:04 PM, Ian Main wrote:
> >>> This patch adds sync-modes to the drive-backup interface and
> >>> implements the FULL, NONE and TOP modes of synchronization.
> >>>
> 
> >>> @@ -1807,6 +1807,10 @@
> >>>  # @format: #optional the format of the new destination, default is to
> >>>  #          probe if @mode is 'existing', else the format of the source
> >>>  #
> >>> +# @sync: what parts of the disk image should be copied to the destination
> >>> +#        (all the disk, only the sectors allocated in the topmost image, or
> >>> +#        only new I/O).
> >>> +#
> >>>  # @mode: #optional whether and how QEMU should create a new image, default is
> >>>  #        'absolute-paths'.
> >>
> >> This hunk looks bogus; the 'DriveBackup' type already documents @sync as
> >> of commit b53169e, which makes me suspect this hunk got misapplied
> >> during rebasing.
> > 
> > Did you check that?  I know there was one bit of documentation missing
> > that I fixed here.  I also just did a clean rebase (git am) to
> > kevin/block and it all applied fine.
> 
> Yes, it _applied_ fine, because of git's insistence on applying hunks
> regardless of line fuzzing.  It probably applied to 'drive-mirror',
> since I see this context in the section for 'drive-mirror' when reading
> the unpatched file at current qemu.git head:
> 
> > # @format: #optional the format of the new destination, default is to
> > #          probe if @mode is 'existing', else the format of the source
> > #
> > # @mode: #optional whether and how QEMU should create a new image, default is
> > #        'absolute-paths'.
> > #
> 
> Hence, my argument that you DON'T want this hunk.

Ah, yes you are right.  I'll fix it next rev along with other things
mentioned.

	Ian