[Qemu-devel] [PATCH for 2.5 v8 0/10] dataplane snapshot fixes

[Qemu-devel] [PATCH for 2.5 v8 0/10] dataplane snapshot fixes

[Denis V. Lunev]

with test
    while /bin/true ; do
        virsh snapshot-create rhel7
        sleep 10
        virsh snapshot-delete rhel7 --current
    done
with enabled iothreads on a running VM leads to a lot of troubles: hangs,
asserts, errors.

Anyway, I think that the construction like
    assert(aio_context_is_locked(aio_context));
should be widely used to ensure proper locking.

Changes from v7:
- patch 5: fixes for bdrv_all_find_snapshot. Changed parameter name to
  skip_read_only which better reflects the meaning of the value and
  fixed checks inside to conform the note from Stefan

Changes from v6:
- tricky part dropped from patch 7
- patch 5 reworked to process snapshot list differently in info commands
  and on savevm

Changes from v5:
- dropped already merged patch 11
- fixed spelling in patch 1
- changed order of condition in loops in all patches. Thank you Stefan
- dropped patch 9
- aio_context is not acquired any more in bdrv_all_find_vmstate_bs by request
  of Stefan
- patch 10 is implemented in completely different way

Changes from v4:
- only migration/savevm.c code and monitor is affected now. Generic block
  layer stuff will be sent separately to speedup merging. The approach
  in general was negotiated with Juan and Stefan.

Changes from v3:
- more places found
- new aio_poll concept, see patch 10

Changes from v2:
- droppped patch 5 as already merged
- changed locking scheme in patch 4 by suggestion of Juan

Changes from v1:
- aio-context locking added
- comment is rewritten

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>

Denis V. Lunev (10):
  snapshot: create helper to test that block drivers supports snapshots
  snapshot: return error code from bdrv_snapshot_delete_by_id_or_name
  snapshot: create bdrv_all_delete_snapshot helper
  snapshot: create bdrv_all_goto_snapshot helper
  snapshot: create bdrv_all_find_snapshot helper
  migration: drop find_vmstate_bs check in hmp_delvm
  snapshot: create bdrv_all_create_snapshot helper
  migration: reorder processing in hmp_savevm
  migration: implement bdrv_all_find_vmstate_bs helper
  migration: normalize locking in migration/savevm.c

 block/snapshot.c         | 135 ++++++++++++++++++++++++++++++-
 include/block/snapshot.h |  25 +++++-
 migration/savevm.c       | 207 +++++++++++++++--------------------------------
 3 files changed, 217 insertions(+), 150 deletions(-)
-- 
2.5.0

[Qemu-devel] [PATCH 01/10] snapshot: create helper to test that block drivers supports snapshots

[Denis V. Lunev]

The patch enforces proper locking for this operation.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 24 ++++++++++++++++++++++++
 include/block/snapshot.h |  8 ++++++++
 migration/savevm.c       | 17 ++++-------------
 3 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index 89500f2..d929d08 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -356,3 +356,27 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
 
     return ret;
 }
+
+
+/* Group operations. All block drivers are involved.
+ * These functions will properly handle dataplane (take aio_context_acquire
+ * when appropriate for appropriate block drivers) */
+
+bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)
+{
+    bool ok = true;
+    BlockDriverState *bs = NULL;
+
+    while (ok && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        if (bdrv_is_inserted(bs) && !bdrv_is_read_only(bs)) {
+            ok = bdrv_can_snapshot(bs);
+        }
+        aio_context_release(ctx);
+    }
+
+    *first_bad_bs = bs;
+    return ok;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 770d9bb..6195c9c 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -75,4 +75,12 @@ int bdrv_snapshot_load_tmp(BlockDriverState *bs,
 int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
                                          const char *id_or_name,
                                          Error **errp);
+
+
+/* Group operations. All block drivers are involved.
+ * These functions will properly handle dataplane (take aio_context_acquire
+ * when appropriate for appropriate block drivers */
+
+bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs);
+
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index d90e228..4646aa1 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1958,19 +1958,10 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     const char *name = qdict_get_try_str(qdict, "name");
     Error *local_err = NULL;
 
-    /* Verify if there is a device that doesn't support snapshots and is writable */
-    bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-
-        if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
-            continue;
-        }
-
-        if (!bdrv_can_snapshot(bs)) {
-            monitor_printf(mon, "Device '%s' is writable but does not support snapshots.\n",
-                               bdrv_get_device_name(bs));
-            return;
-        }
+    if (!bdrv_all_can_snapshot(&bs)) {
+        monitor_printf(mon, "Device '%s' is writable but does not "
+                       "support snapshots.\n", bdrv_get_device_name(bs));
+        return;
     }
 
     bs = find_vmstate_bs();
-- 
2.5.0

[Qemu-devel] [PATCH 02/10] snapshot: return error code from bdrv_snapshot_delete_by_id_or_name

[Denis V. Lunev]

this will make code better in the next patch

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 7 ++++---
 include/block/snapshot.h | 6 +++---
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index d929d08..ed0422d 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -253,9 +253,9 @@ int bdrv_snapshot_delete(BlockDriverState *bs,
     return -ENOTSUP;
 }
 
-void bdrv_snapshot_delete_by_id_or_name(BlockDriverState *bs,
-                                        const char *id_or_name,
-                                        Error **errp)
+int bdrv_snapshot_delete_by_id_or_name(BlockDriverState *bs,
+                                       const char *id_or_name,
+                                       Error **errp)
 {
     int ret;
     Error *local_err = NULL;
@@ -270,6 +270,7 @@ void bdrv_snapshot_delete_by_id_or_name(BlockDriverState *bs,
     if (ret < 0) {
         error_propagate(errp, local_err);
     }
+    return ret;
 }
 
 int bdrv_snapshot_list(BlockDriverState *bs,
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 6195c9c..9ddfd42 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -63,9 +63,9 @@ int bdrv_snapshot_delete(BlockDriverState *bs,
                          const char *snapshot_id,
                          const char *name,
                          Error **errp);
-void bdrv_snapshot_delete_by_id_or_name(BlockDriverState *bs,
-                                        const char *id_or_name,
-                                        Error **errp);
+int bdrv_snapshot_delete_by_id_or_name(BlockDriverState *bs,
+                                       const char *id_or_name,
+                                       Error **errp);
 int bdrv_snapshot_list(BlockDriverState *bs,
                        QEMUSnapshotInfo **psn_info);
 int bdrv_snapshot_load_tmp(BlockDriverState *bs,
-- 
2.5.0

[Qemu-devel] [PATCH 03/10] snapshot: create bdrv_all_delete_snapshot helper

[Denis V. Lunev]

to delete snapshots from all loaded block drivers.

The patch also ensures proper locking.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 22 ++++++++++++++++++++
 include/block/snapshot.h |  2 ++
 migration/savevm.c       | 54 +++++++++---------------------------------------
 3 files changed, 34 insertions(+), 44 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index ed0422d..61a6ad1 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -381,3 +381,25 @@ bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs)
     *first_bad_bs = bs;
     return ok;
 }
+
+int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bad_bs,
+                             Error **err)
+{
+    int ret = 0;
+    BlockDriverState *bs = NULL;
+    QEMUSnapshotInfo sn1, *snapshot = &sn1;
+
+    while (ret == 0 && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        if (bdrv_can_snapshot(bs) &&
+                bdrv_snapshot_find(bs, snapshot, name) >= 0) {
+            ret = bdrv_snapshot_delete_by_id_or_name(bs, name, err);
+        }
+        aio_context_release(ctx);
+    }
+
+    *first_bad_bs = bs;
+    return ret;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 9ddfd42..d02d2b1 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -82,5 +82,7 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
  * when appropriate for appropriate block drivers */
 
 bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs);
+int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bsd_bs,
+                             Error **err);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index 4646aa1..c52cbbe 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1916,35 +1916,6 @@ static BlockDriverState *find_vmstate_bs(void)
     return NULL;
 }
 
-/*
- * Deletes snapshots of a given name in all opened images.
- */
-static int del_existing_snapshots(Monitor *mon, const char *name)
-{
-    BlockDriverState *bs;
-    QEMUSnapshotInfo sn1, *snapshot = &sn1;
-    Error *err = NULL;
-
-    bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-        if (bdrv_can_snapshot(bs) &&
-            bdrv_snapshot_find(bs, snapshot, name) >= 0) {
-            bdrv_snapshot_delete_by_id_or_name(bs, name, &err);
-            if (err) {
-                monitor_printf(mon,
-                               "Error while deleting snapshot on device '%s':"
-                               " %s\n",
-                               bdrv_get_device_name(bs),
-                               error_get_pretty(err));
-                error_free(err);
-                return -1;
-            }
-        }
-    }
-
-    return 0;
-}
-
 void hmp_savevm(Monitor *mon, const QDict *qdict)
 {
     BlockDriverState *bs, *bs1;
@@ -2002,7 +1973,11 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     }
 
     /* Delete old snapshots of the same name */
-    if (name && del_existing_snapshots(mon, name) < 0) {
+    if (name && bdrv_all_delete_snapshot(name, &bs1, &local_err) < 0) {
+        monitor_printf(mon,
+                       "Error while deleting snapshot on device '%s': %s\n",
+                       bdrv_get_device_name(bs1), error_get_pretty(local_err));
+        error_free(local_err);
         goto the_end;
     }
 
@@ -2162,20 +2137,11 @@ void hmp_delvm(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-        if (bdrv_can_snapshot(bs)) {
-            err = NULL;
-            bdrv_snapshot_delete_by_id_or_name(bs, name, &err);
-            if (err) {
-                monitor_printf(mon,
-                               "Error while deleting snapshot on device '%s':"
-                               " %s\n",
-                               bdrv_get_device_name(bs),
-                               error_get_pretty(err));
-                error_free(err);
-            }
-        }
+    if (bdrv_all_delete_snapshot(name, &bs, &err) < 0) {
+        monitor_printf(mon,
+                       "Error while deleting snapshot on device '%s': %s\n",
+                       bdrv_get_device_name(bs), error_get_pretty(err));
+        error_free(err);
     }
 }
 
-- 
2.5.0

[Qemu-devel] [PATCH 04/10] snapshot: create bdrv_all_goto_snapshot helper

[Denis V. Lunev]

to switch to snapshot on all loaded block drivers.

The patch also ensures proper locking.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 20 ++++++++++++++++++++
 include/block/snapshot.h |  1 +
 migration/savevm.c       | 15 +++++----------
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index 61a6ad1..9f07a63 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -403,3 +403,23 @@ int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bad_bs,
     *first_bad_bs = bs;
     return ret;
 }
+
+
+int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bad_bs)
+{
+    int err = 0;
+    BlockDriverState *bs = NULL;
+
+    while (err == 0 && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        if (bdrv_can_snapshot(bs)) {
+            err = bdrv_snapshot_goto(bs, name);
+        }
+        aio_context_release(ctx);
+    }
+
+    *first_bad_bs = bs;
+    return err;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index d02d2b1..0a176c7 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -84,5 +84,6 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
 bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs);
 int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bsd_bs,
                              Error **err);
+int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bsd_bs);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index c52cbbe..254e51d 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2093,16 +2093,11 @@ int load_vmstate(const char *name)
     /* Flush all IO requests so they don't interfere with the new state.  */
     bdrv_drain_all();
 
-    bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-        if (bdrv_can_snapshot(bs)) {
-            ret = bdrv_snapshot_goto(bs, name);
-            if (ret < 0) {
-                error_report("Error %d while activating snapshot '%s' on '%s'",
-                             ret, name, bdrv_get_device_name(bs));
-                return ret;
-            }
-        }
+    ret = bdrv_all_goto_snapshot(name, &bs);
+    if (ret < 0) {
+        error_report("Error %d while activating snapshot '%s' on '%s'",
+                     ret, name, bdrv_get_device_name(bs));
+        return ret;
     }
 
     /* restore the VM state */
-- 
2.5.0

[Qemu-devel] [PATCH 05/10] snapshot: create bdrv_all_find_snapshot helper

[Denis V. Lunev]

to check that snapshot is available for all loaded block drivers. The
ability to switch to snapshot is verified separately using
bdrv_all_can_snapshot.

The patch also ensures proper locking.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 26 +++++++++++++++++++++++
 include/block/snapshot.h |  2 ++
 migration/savevm.c       | 55 +++++++++++++-----------------------------------
 3 files changed, 43 insertions(+), 40 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index 9f07a63..eb82873 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -423,3 +423,29 @@ int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bad_bs)
     *first_bad_bs = bs;
     return err;
 }
+
+int bdrv_all_find_snapshot(const char *name, bool skip_read_only,
+                           BlockDriverState **first_bad_bs)
+{
+    QEMUSnapshotInfo sn;
+    int err = 0;
+    BlockDriverState *bs = NULL;
+
+    while (err == 0 && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        if (skip_read_only &&
+                (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs))) {
+            continue;
+        }
+
+        aio_context_acquire(ctx);
+        if (bdrv_can_snapshot(bs)) {
+            err = bdrv_snapshot_find(bs, &sn, name);
+        }
+        aio_context_release(ctx);
+    }
+
+    *first_bad_bs = bs;
+    return err;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 0a176c7..431360a 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -85,5 +85,7 @@ bool bdrv_all_can_snapshot(BlockDriverState **first_bad_bs);
 int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bsd_bs,
                              Error **err);
 int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bsd_bs);
+int bdrv_all_find_snapshot(const char *name, bool skip_read_only,
+                           BlockDriverState **first_bad_bs);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index 254e51d..a391b3a 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2051,6 +2051,18 @@ int load_vmstate(const char *name)
     QEMUFile *f;
     int ret;
 
+    if (!bdrv_all_can_snapshot(&bs)) {
+        error_report("Device '%s' is writable but does not support snapshots.",
+                     bdrv_get_device_name(bs));
+        return -ENOTSUP;
+    }
+    ret = bdrv_all_find_snapshot(name, true, &bs);
+    if (ret < 0) {
+        error_report("Device '%s' does not have the requested snapshot '%s'",
+                     bdrv_get_device_name(bs), name);
+        return ret;
+    }
+
     bs_vm_state = find_vmstate_bs();
     if (!bs_vm_state) {
         error_report("No block device supports snapshots");
@@ -2067,29 +2079,6 @@ int load_vmstate(const char *name)
         return -EINVAL;
     }
 
-    /* Verify if there is any device that doesn't support snapshots and is
-    writable and check if the requested snapshot is available too. */
-    bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-
-        if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
-            continue;
-        }
-
-        if (!bdrv_can_snapshot(bs)) {
-            error_report("Device '%s' is writable but does not support snapshots.",
-                               bdrv_get_device_name(bs));
-            return -ENOTSUP;
-        }
-
-        ret = bdrv_snapshot_find(bs, &sn, name);
-        if (ret < 0) {
-            error_report("Device '%s' does not have the requested snapshot '%s'",
-                           bdrv_get_device_name(bs), name);
-            return ret;
-        }
-    }
-
     /* Flush all IO requests so they don't interfere with the new state.  */
     bdrv_drain_all();
 
@@ -2143,8 +2132,8 @@ void hmp_delvm(Monitor *mon, const QDict *qdict)
 void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
 {
     BlockDriverState *bs, *bs1;
-    QEMUSnapshotInfo *sn_tab, *sn, s, *sn_info = &s;
-    int nb_sns, i, ret, available;
+    QEMUSnapshotInfo *sn_tab, *sn;
+    int nb_sns, i;
     int total;
     int *available_snapshots;
 
@@ -2168,21 +2157,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     available_snapshots = g_new0(int, nb_sns);
     total = 0;
     for (i = 0; i < nb_sns; i++) {
-        sn = &sn_tab[i];
-        available = 1;
-        bs1 = NULL;
-
-        while ((bs1 = bdrv_next(bs1))) {
-            if (bdrv_can_snapshot(bs1) && bs1 != bs) {
-                ret = bdrv_snapshot_find(bs1, sn_info, sn->id_str);
-                if (ret < 0) {
-                    available = 0;
-                    break;
-                }
-            }
-        }
-
-        if (available) {
+        if (bdrv_all_find_snapshot(sn_tab[i].id_str, false, &bs1) == 0) {
             available_snapshots[total] = i;
             total++;
         }
-- 
2.5.0

[Qemu-devel] [PATCH 06/10] migration: drop find_vmstate_bs check in hmp_delvm

[Denis V. Lunev]

There is no much sense to do the check and write warning.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
---
 migration/savevm.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index a391b3a..68af80e 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2116,11 +2116,6 @@ void hmp_delvm(Monitor *mon, const QDict *qdict)
     Error *err;
     const char *name = qdict_get_str(qdict, "name");
 
-    if (!find_vmstate_bs()) {
-        monitor_printf(mon, "No block device supports snapshots\n");
-        return;
-    }
-
     if (bdrv_all_delete_snapshot(name, &bs, &err) < 0) {
         monitor_printf(mon,
                        "Error while deleting snapshot on device '%s': %s\n",
-- 
2.5.0

[Qemu-devel] [PATCH 07/10] snapshot: create bdrv_all_create_snapshot helper

[Denis V. Lunev]

to create snapshot for all loaded block drivers.

The patch also ensures proper locking.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 26 ++++++++++++++++++++++++++
 include/block/snapshot.h |  4 ++++
 migration/savevm.c       | 17 ++++-------------
 3 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index eb82873..1852328 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -449,3 +449,29 @@ int bdrv_all_find_snapshot(const char *name, bool skip_read_only,
     *first_bad_bs = bs;
     return err;
 }
+
+int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
+                             BlockDriverState *vm_state_bs,
+                             uint64_t vm_state_size,
+                             BlockDriverState **first_bad_bs)
+{
+    int err = 0;
+    BlockDriverState *bs = NULL;
+
+    while (err == 0 && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        if (bs == vm_state_bs) {
+            sn->vm_state_size = vm_state_size;
+            err = bdrv_snapshot_create(bs, sn);
+        } else if (bdrv_can_snapshot(bs)) {
+            sn->vm_state_size = 0;
+            err = bdrv_snapshot_create(bs, sn);
+        }
+        aio_context_release(ctx);
+    }
+
+    *first_bad_bs = bs;
+    return err;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index 431360a..f4f6409 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -87,5 +87,9 @@ int bdrv_all_delete_snapshot(const char *name, BlockDriverState **first_bsd_bs,
 int bdrv_all_goto_snapshot(const char *name, BlockDriverState **first_bsd_bs);
 int bdrv_all_find_snapshot(const char *name, bool skip_read_only,
                            BlockDriverState **first_bad_bs);
+int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
+                             BlockDriverState *vm_state_bs,
+                             uint64_t vm_state_size,
+                             BlockDriverState **first_bad_bs);
 
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index 68af80e..b004f84 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1996,19 +1996,10 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         goto the_end;
     }
 
-    /* create the snapshots */
-
-    bs1 = NULL;
-    while ((bs1 = bdrv_next(bs1))) {
-        if (bdrv_can_snapshot(bs1)) {
-            /* Write VM state size only to the image that contains the state */
-            sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
-            ret = bdrv_snapshot_create(bs1, sn);
-            if (ret < 0) {
-                monitor_printf(mon, "Error while creating snapshot on '%s'\n",
-                               bdrv_get_device_name(bs1));
-            }
-        }
+    ret = bdrv_all_create_snapshot(sn, bs, vm_state_size, &bs);
+    if (ret < 0) {
+        monitor_printf(mon, "Error while creating snapshot on '%s'\n",
+                       bdrv_get_device_name(bs));
     }
 
  the_end:
-- 
2.5.0

[Qemu-devel] [PATCH 08/10] migration: reorder processing in hmp_savevm

[Denis V. Lunev]

State deletion can be performed on running VM which reduces VM downtime
This approach looks a bit more natural.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
---
 migration/savevm.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index b004f84..9ec9117 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1935,6 +1935,15 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         return;
     }
 
+    /* Delete old snapshots of the same name */
+    if (name && bdrv_all_delete_snapshot(name, &bs1, &local_err) < 0) {
+        monitor_printf(mon,
+                       "Error while deleting snapshot on device '%s': %s\n",
+                       bdrv_get_device_name(bs1), error_get_pretty(local_err));
+        error_free(local_err);
+        return;
+    }
+
     bs = find_vmstate_bs();
     if (!bs) {
         monitor_printf(mon, "No block device can accept snapshots\n");
@@ -1972,15 +1981,6 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         strftime(sn->name, sizeof(sn->name), "vm-%Y%m%d%H%M%S", &tm);
     }
 
-    /* Delete old snapshots of the same name */
-    if (name && bdrv_all_delete_snapshot(name, &bs1, &local_err) < 0) {
-        monitor_printf(mon,
-                       "Error while deleting snapshot on device '%s': %s\n",
-                       bdrv_get_device_name(bs1), error_get_pretty(local_err));
-        error_free(local_err);
-        goto the_end;
-    }
-
     /* save the VM state */
     f = qemu_fopen_bdrv(bs, 1);
     if (!f) {
-- 
2.5.0

[Qemu-devel] [PATCH 09/10] migration: implement bdrv_all_find_vmstate_bs helper

[Denis V. Lunev]

The patch also ensures proper locking for the operation.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/snapshot.c         | 15 +++++++++++++++
 include/block/snapshot.h |  2 ++
 migration/savevm.c       | 19 ++++---------------
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/block/snapshot.c b/block/snapshot.c
index 1852328..6ccb1c9 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -475,3 +475,18 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
     *first_bad_bs = bs;
     return err;
 }
+
+BlockDriverState *bdrv_all_find_vmstate_bs(void)
+{
+    bool not_found = true;
+    BlockDriverState *bs = NULL;
+
+    while (not_found && (bs = bdrv_next(bs))) {
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
+        not_found = !bdrv_can_snapshot(bs);
+        aio_context_release(ctx);
+    }
+    return bs;
+}
diff --git a/include/block/snapshot.h b/include/block/snapshot.h
index f4f6409..c925105 100644
--- a/include/block/snapshot.h
+++ b/include/block/snapshot.h
@@ -92,4 +92,6 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
                              uint64_t vm_state_size,
                              BlockDriverState **first_bad_bs);
 
+BlockDriverState *bdrv_all_find_vmstate_bs(void);
+
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index 9ec9117..953b559 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1905,17 +1905,6 @@ int qemu_loadvm_state(QEMUFile *f)
     return ret;
 }
 
-static BlockDriverState *find_vmstate_bs(void)
-{
-    BlockDriverState *bs = NULL;
-    while ((bs = bdrv_next(bs))) {
-        if (bdrv_can_snapshot(bs)) {
-            return bs;
-        }
-    }
-    return NULL;
-}
-
 void hmp_savevm(Monitor *mon, const QDict *qdict)
 {
     BlockDriverState *bs, *bs1;
@@ -1944,8 +1933,8 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    bs = find_vmstate_bs();
-    if (!bs) {
+    bs = bdrv_all_find_vmstate_bs();
+    if (bs == NULL) {
         monitor_printf(mon, "No block device can accept snapshots\n");
         return;
     }
@@ -2054,7 +2043,7 @@ int load_vmstate(const char *name)
         return ret;
     }
 
-    bs_vm_state = find_vmstate_bs();
+    bs_vm_state = bdrv_all_find_vmstate_bs();
     if (!bs_vm_state) {
         error_report("No block device supports snapshots");
         return -ENOTSUP;
@@ -2123,7 +2112,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     int total;
     int *available_snapshots;
 
-    bs = find_vmstate_bs();
+    bs = bdrv_all_find_vmstate_bs();
     if (!bs) {
         monitor_printf(mon, "No available block device supports snapshots\n");
         return;
-- 
2.5.0

[Qemu-devel] [PATCH 10/10] migration: normalize locking in migration/savevm.c

[Denis V. Lunev]

basically all bdrv_* operations must be called under aio_context_acquire
except ones with bdrv_all prefix.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
---
 migration/savevm.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index 953b559..2c65ab2 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1917,6 +1917,7 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     struct tm tm;
     const char *name = qdict_get_try_str(qdict, "name");
     Error *local_err = NULL;
+    AioContext *aio_context;
 
     if (!bdrv_all_can_snapshot(&bs)) {
         monitor_printf(mon, "Device '%s' is writable but does not "
@@ -1938,6 +1939,7 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "No block device can accept snapshots\n");
         return;
     }
+    aio_context = bdrv_get_aio_context(bs);
 
     saved_vm_running = runstate_is_running();
 
@@ -1948,6 +1950,8 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     }
     vm_stop(RUN_STATE_SAVE_VM);
 
+    aio_context_acquire(aio_context);
+
     memset(sn, 0, sizeof(*sn));
 
     /* fill auxiliary fields */
@@ -1992,6 +1996,7 @@ void hmp_savevm(Monitor *mon, const QDict *qdict)
     }
 
  the_end:
+    aio_context_release(aio_context);
     if (saved_vm_running) {
         vm_start();
     }
@@ -2030,6 +2035,7 @@ int load_vmstate(const char *name)
     QEMUSnapshotInfo sn;
     QEMUFile *f;
     int ret;
+    AioContext *aio_context;
 
     if (!bdrv_all_can_snapshot(&bs)) {
         error_report("Device '%s' is writable but does not support snapshots.",
@@ -2048,9 +2054,12 @@ int load_vmstate(const char *name)
         error_report("No block device supports snapshots");
         return -ENOTSUP;
     }
+    aio_context = bdrv_get_aio_context(bs);
 
     /* Don't even try to load empty VM states */
+    aio_context_acquire(aio_context);
     ret = bdrv_snapshot_find(bs_vm_state, &sn, name);
+    aio_context_release(aio_context);
     if (ret < 0) {
         return ret;
     } else if (sn.vm_state_size == 0) {
@@ -2078,9 +2087,12 @@ int load_vmstate(const char *name)
 
     qemu_system_reset(VMRESET_SILENT);
     migration_incoming_state_new(f);
-    ret = qemu_loadvm_state(f);
 
+    aio_context_acquire(aio_context);
+    ret = qemu_loadvm_state(f);
     qemu_fclose(f);
+    aio_context_release(aio_context);
+
     migration_incoming_state_destroy();
     if (ret < 0) {
         error_report("Error %d while loading VM state", ret);
@@ -2111,14 +2123,19 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     int nb_sns, i;
     int total;
     int *available_snapshots;
+    AioContext *aio_context;
 
     bs = bdrv_all_find_vmstate_bs();
     if (!bs) {
         monitor_printf(mon, "No available block device supports snapshots\n");
         return;
     }
+    aio_context = bdrv_get_aio_context(bs);
 
+    aio_context_acquire(aio_context);
     nb_sns = bdrv_snapshot_list(bs, &sn_tab);
+    aio_context_release(aio_context);
+
     if (nb_sns < 0) {
         monitor_printf(mon, "bdrv_snapshot_list: error %d\n", nb_sns);
         return;
-- 
2.5.0

Re: [Qemu-devel] [PATCH 05/10] snapshot: create bdrv_all_find_snapshot helper

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 2084 bytes --]

On Mon, Nov 16, 2015 at 06:24:36PM +0300, Denis V. Lunev wrote:
> +int bdrv_all_find_snapshot(const char *name, bool skip_read_only,
> +                           BlockDriverState **first_bad_bs)
> +{
> +    QEMUSnapshotInfo sn;
> +    int err = 0;
> +    BlockDriverState *bs = NULL;
> +
> +    while (err == 0 && (bs = bdrv_next(bs))) {
> +        AioContext *ctx = bdrv_get_aio_context(bs);
> +
> +        if (skip_read_only &&
> +                (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs))) {

These must be called with AioContext acquired.

> +            continue;
> +        }
> +
> +        aio_context_acquire(ctx);
> +        if (bdrv_can_snapshot(bs)) {

The !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) checks above are
redundant since bdrv_can_snapshot() checks too:

  int bdrv_can_snapshot(BlockDriverState *bs)
  {
      BlockDriver *drv = bs->drv;
      if (!drv || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
          return 0;
      }

It also means that the "skip_read_only" name is inaccurate.  Read-only
drives are always skipped, regardless of skip_read_only's value.

The skip_read_only argument can be dropped and the earlier
!bdrv_is_inserted(bs) || bdrv_is_read_only(bs) check can be dropped too.

> @@ -2168,21 +2157,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
>      available_snapshots = g_new0(int, nb_sns);
>      total = 0;
>      for (i = 0; i < nb_sns; i++) {
> -        sn = &sn_tab[i];
> -        available = 1;
> -        bs1 = NULL;
> -
> -        while ((bs1 = bdrv_next(bs1))) {
> -            if (bdrv_can_snapshot(bs1) && bs1 != bs) {
> -                ret = bdrv_snapshot_find(bs1, sn_info, sn->id_str);
> -                if (ret < 0) {
> -                    available = 0;
> -                    break;
> -                }
> -            }
> -        }
> -
> -        if (available) {
> +        if (bdrv_all_find_snapshot(sn_tab[i].id_str, false, &bs1) == 0) {

bdrv_all_find_snapshot() doesn't do the bs1 != bs exclusion so the new
code behaves differently from the old code.  That seems like a bug.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 473 bytes --]

Re: [Qemu-devel] [PATCH 05/10] snapshot: create bdrv_all_find_snapshot helper

[Denis V. Lunev]

On 11/17/2015 10:22 AM, Stefan Hajnoczi wrote:
> On Mon, Nov 16, 2015 at 06:24:36PM +0300, Denis V. Lunev wrote:
>> +int bdrv_all_find_snapshot(const char *name, bool skip_read_only,
>> +                           BlockDriverState **first_bad_bs)
>> +{
>> +    QEMUSnapshotInfo sn;
>> +    int err = 0;
>> +    BlockDriverState *bs = NULL;
>> +
>> +    while (err == 0 && (bs = bdrv_next(bs))) {
>> +        AioContext *ctx = bdrv_get_aio_context(bs);
>> +
>> +        if (skip_read_only &&
>> +                (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs))) {
> These must be called with AioContext acquired.
>

AFAIK no. this is called without that in bdrv jobs code.

bdrv_is_read_only is a simple flag, which is filled on open
bdrv_is_inserted is defined for CDROM only and does
not rely on AIO context stuff.

>> +            continue;
>> +        }
>> +
>> +        aio_context_acquire(ctx);
>> +        if (bdrv_can_snapshot(bs)) {
> The !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) checks above are
> redundant since bdrv_can_snapshot() checks too:
>
>    int bdrv_can_snapshot(BlockDriverState *bs)
>    {
>        BlockDriver *drv = bs->drv;
>        if (!drv || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
>            return 0;
>        }
>
> It also means that the "skip_read_only" name is inaccurate.  Read-only
> drives are always skipped, regardless of skip_read_only's value.
>
> The skip_read_only argument can be dropped and the earlier
> !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) check can be dropped too.
I have though on this several times and once again I am wrong :(
This looks like a punishment for my sins. OK :(


>> @@ -2168,21 +2157,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
>>       available_snapshots = g_new0(int, nb_sns);
>>       total = 0;
>>       for (i = 0; i < nb_sns; i++) {
>> -        sn = &sn_tab[i];
>> -        available = 1;
>> -        bs1 = NULL;
>> -
>> -        while ((bs1 = bdrv_next(bs1))) {
>> -            if (bdrv_can_snapshot(bs1) && bs1 != bs) {
>> -                ret = bdrv_snapshot_find(bs1, sn_info, sn->id_str);
>> -                if (ret < 0) {
>> -                    available = 0;
>> -                    break;
>> -                }
>> -            }
>> -        }
>> -
>> -        if (available) {
>> +        if (bdrv_all_find_snapshot(sn_tab[i].id_str, false, &bs1) == 0) {
> bdrv_all_find_snapshot() doesn't do the bs1 != bs exclusion so the new
> code behaves differently from the old code.  That seems like a bug.
no. The result will be the same. This is a minor optimisation:
- we get the first block device we can make snapshot on
- we get snapshot list on that device
- after that we start iterations over the list and removing not 
available snapshots on other devices
This means that if bs == bs1 the check will be "always true"

Re: [Qemu-devel] [PATCH 05/10] snapshot: create bdrv_all_find_snapshot helper

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1433 bytes --]

On Tue, Nov 17, 2015 at 11:10:26AM +0300, Denis V. Lunev wrote:
> On 11/17/2015 10:22 AM, Stefan Hajnoczi wrote:
> >On Mon, Nov 16, 2015 at 06:24:36PM +0300, Denis V. Lunev wrote:
> >>@@ -2168,21 +2157,7 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
> >>      available_snapshots = g_new0(int, nb_sns);
> >>      total = 0;
> >>      for (i = 0; i < nb_sns; i++) {
> >>-        sn = &sn_tab[i];
> >>-        available = 1;
> >>-        bs1 = NULL;
> >>-
> >>-        while ((bs1 = bdrv_next(bs1))) {
> >>-            if (bdrv_can_snapshot(bs1) && bs1 != bs) {
> >>-                ret = bdrv_snapshot_find(bs1, sn_info, sn->id_str);
> >>-                if (ret < 0) {
> >>-                    available = 0;
> >>-                    break;
> >>-                }
> >>-            }
> >>-        }
> >>-
> >>-        if (available) {
> >>+        if (bdrv_all_find_snapshot(sn_tab[i].id_str, false, &bs1) == 0) {
> >bdrv_all_find_snapshot() doesn't do the bs1 != bs exclusion so the new
> >code behaves differently from the old code.  That seems like a bug.
> no. The result will be the same. This is a minor optimisation:
> - we get the first block device we can make snapshot on
> - we get snapshot list on that device
> - after that we start iterations over the list and removing not available
> snapshots on other devices
> This means that if bs == bs1 the check will be "always true"

Ah, I see.  Thanks!

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 473 bytes --]