[Qemu-devel] [PATCH v2 0/3] block devices record/replay update

[Qemu-devel] [PATCH v2 0/3] block devices record/replay update

[Pavel Dovgalyuk]

This set of patches includes several fixes for preserving
the state of the block device images while recording and replaying
virtual machine execution.

blkreplay driver now creates temporary overlay for underlaying devices
This patch implicitly enables '-snapshot' behavior in record/replay mode.
blkreplay layer creates temporary overlays on top of underlaying
disk images. It is needed, because creating an overlay over blkreplay
with explicit '-snapshot' option breaks the determinism.

v2 changes:
 - removed useless bdrv_ref/unref calls (as suggested by Kevin Wolf)
 - updated commit messages
 - minor changes

---

Pavel Dovgalyuk (3):
      block: implement bdrv_snapshot_goto for blkreplay
      blkreplay: create temporary overlay for underlaying devices
      replay: disable default snapshot for record/replay


 block/blkreplay.c |   73 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 stubs/replay.c    |    1 +
 vl.c              |   10 ++++++-
 3 files changed, 82 insertions(+), 2 deletions(-)

-- 
Pavel Dovgalyuk

[Qemu-devel] [PATCH v2 1/3] block: implement bdrv_snapshot_goto for blkreplay

[Pavel Dovgalyuk]

This patch enables making snapshots with blkreplay used in
block devices.
This function is required to make bdrv_snapshot_goto without
calling .bdrv_open which is not implemented.

v2: updated commit message

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
---
 block/blkreplay.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/blkreplay.c b/block/blkreplay.c
index cfc8c5b..ddcf344 100644
--- a/block/blkreplay.c
+++ b/block/blkreplay.c
@@ -130,6 +130,12 @@ static int coroutine_fn blkreplay_co_flush(BlockDriverState *bs)
     return ret;
 }
 
+static int blkreplay_snapshot_goto(BlockDriverState *bs,
+                                   const char *snapshot_id)
+{
+    return bdrv_snapshot_goto(bs->file->bs, snapshot_id);
+}
+
 static BlockDriver bdrv_blkreplay = {
     .format_name            = "blkreplay",
     .protocol_name          = "blkreplay",
@@ -145,6 +151,8 @@ static BlockDriver bdrv_blkreplay = {
     .bdrv_co_pwrite_zeroes  = blkreplay_co_pwrite_zeroes,
     .bdrv_co_pdiscard       = blkreplay_co_pdiscard,
     .bdrv_co_flush          = blkreplay_co_flush,
+
+    .bdrv_snapshot_goto     = blkreplay_snapshot_goto,
 };
 
 static void bdrv_blkreplay_init(void)

Re: [Qemu-devel] [PATCH v2 1/3] block: implement bdrv_snapshot_goto for blkreplay

[Eric Blake]

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On 02/28/2017 04:55 AM, Pavel Dovgalyuk wrote:

[meta-comment]

> This patch enables making snapshots with blkreplay used in
> block devices.
> This function is required to make bdrv_snapshot_goto without
> calling .bdrv_open which is not implemented.
> 
> v2: updated commit message

The v2 information...

> 
> Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
> ---

...fits best here. Anything after the --- is stripped by 'git am',
making it ideal for information that is useful to the reviewers but not
important to a long-term reader (a year from now, we won't care if it
was v2 or v10 that was committed, because git only stores the version
that was checked in, and not the iterations prior to it).

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


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[Qemu-devel] [PATCH v2 2/3] blkreplay: create temporary overlay for underlaying devices

[Pavel Dovgalyuk]

This patch allows using '-snapshot' behavior in record/replay mode.
blkreplay layer creates temporary overlays on top of underlaying
disk images. It is needed, because creating an overlay over blkreplay
breaks the determinism.
This patch creates similar temporary overlay (when it is needed)
under the blkreplay driver. Therefore all block operations are controlled
by blkreplay.

v2: removed useless ref/unref (as suggested by Kevin Wolf)

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
---
 block/blkreplay.c |   65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 stubs/replay.c    |    1 +
 vl.c              |    2 +-
 3 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/block/blkreplay.c b/block/blkreplay.c
index ddcf344..de91def 100644
--- a/block/blkreplay.c
+++ b/block/blkreplay.c
@@ -14,12 +14,69 @@
 #include "block/block_int.h"
 #include "sysemu/replay.h"
 #include "qapi/error.h"
+#include "qapi/qmp/qstring.h"
 
 typedef struct Request {
     Coroutine *co;
     QEMUBH *bh;
 } Request;
 
+static BlockDriverState *blkreplay_append_snapshot(BlockDriverState *bs,
+                                                   Error **errp)
+{
+    int ret;
+    BlockDriverState *bs_snapshot;
+    int64_t total_size;
+    QemuOpts *opts = NULL;
+    char tmp_filename[PATH_MAX + 1];
+    QDict *snapshot_options = qdict_new();
+
+    /* Prepare options QDict for the overlay file */
+    qdict_put(snapshot_options, "file.driver", qstring_from_str("file"));
+    qdict_put(snapshot_options, "driver", qstring_from_str("qcow2"));
+
+    /* Create temporary file */
+    ret = get_tmp_filename(tmp_filename, PATH_MAX + 1);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Could not get temporary filename");
+        goto out;
+    }
+    qdict_put(snapshot_options, "file.filename",
+              qstring_from_str(tmp_filename));
+
+    /* Get the required size from the image */
+    total_size = bdrv_getlength(bs);
+    if (total_size < 0) {
+        error_setg_errno(errp, -total_size, "Could not get image size");
+        goto out;
+    }
+
+    opts = qemu_opts_create(bdrv_qcow2.create_opts, NULL, 0, &error_abort);
+    qemu_opt_set_number(opts, BLOCK_OPT_SIZE, total_size, &error_abort);
+    ret = bdrv_create(&bdrv_qcow2, tmp_filename, opts, errp);
+    qemu_opts_del(opts);
+    if (ret < 0) {
+        error_prepend(errp, "Could not create temporary overlay '%s': ",
+                      tmp_filename);
+        goto out;
+    }
+
+    bs_snapshot = bdrv_open(NULL, NULL, snapshot_options,
+                            BDRV_O_RDWR | BDRV_O_TEMPORARY, errp);
+    snapshot_options = NULL;
+    if (!bs_snapshot) {
+        goto out;
+    }
+
+    bdrv_append(bs_snapshot, bs);
+
+    return bs_snapshot;
+
+out:
+    QDECREF(snapshot_options);
+    return NULL;
+}
+
 static int blkreplay_open(BlockDriverState *bs, QDict *options, int flags,
                           Error **errp)
 {
@@ -35,6 +92,14 @@ static int blkreplay_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    /* Add temporary snapshot to preserve the image */
+    if (!replay_snapshot
+        && !blkreplay_append_snapshot(bs->file->bs, &local_err)) {
+        ret = -EINVAL;
+        error_propagate(errp, local_err);
+        goto fail;
+    }
+
     ret = 0;
 fail:
     if (ret < 0) {
diff --git a/stubs/replay.c b/stubs/replay.c
index 9c8aa48..9991ee5 100644
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -3,6 +3,7 @@
 #include "sysemu/sysemu.h"
 
 ReplayMode replay_mode;
+char *replay_snapshot;
 
 int64_t replay_save_clock(unsigned int kind, int64_t clock)
 {
diff --git a/vl.c b/vl.c
index e10a27b..876a55a 100644
--- a/vl.c
+++ b/vl.c
@@ -4450,7 +4450,7 @@ int main(int argc, char **argv, char **envp)
     }
 
     /* open the virtual block devices */
-    if (snapshot || replay_mode != REPLAY_MODE_NONE) {
+    if (snapshot) {
         qemu_opts_foreach(qemu_find_opts("drive"), drive_enable_snapshot,
                           NULL, NULL);
     }

[Qemu-devel] [PATCH v2 3/3] replay: disable default snapshot for record/replay

[Pavel Dovgalyuk]

This patch disables setting '-snapshot' option on by default
in record/replay mode. This is needed for creating vmstates in record
and replay modes.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
---
 vl.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/vl.c b/vl.c
index 876a55a..1b85923 100644
--- a/vl.c
+++ b/vl.c
@@ -3140,7 +3140,13 @@ int main(int argc, char **argv, char **envp)
                 drive_add(IF_PFLASH, -1, optarg, PFLASH_OPTS);
                 break;
             case QEMU_OPTION_snapshot:
-                snapshot = 1;
+                {
+                    Error *blocker = NULL;
+                    snapshot = 1;
+                    error_setg(&blocker, QERR_REPLAY_NOT_SUPPORTED,
+                               "-snapshot");
+                    replay_add_blocker(blocker);
+                }
                 break;
             case QEMU_OPTION_hdachs:
                 {