[libvirt] [PATCH 0/3] qemu: Allow migration with disk cache on
QEMU 4.0.0 and newer automatically drops caches at the end of migration, which means we can safely allow migration even if disk/driver/@cache is not none nor directsync. Jiri Denemark (3): qemu: Clarify error message in qemuMigrationSrcIsSafe qemu: Check for drop-cache capability qemu: Allow migration with disk cache on src/qemu/qemu_capabilities.c | 2 ++ src/qemu/qemu_capabilities.h | 1 + src/qemu/qemu_migration.c | 14 +++++++++++--- tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml | 1 + tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml | 1 + 10 files changed, 21 insertions(+), 3 deletions(-) -- 2.22.1
The original message was logically incorrect: cache != none or cache != directsync is always true. But even replacing "or" with "and" doesn't make it more readable for humans. Signed-off-by: Jiri Denemark <jdenemar@redhat.com> --- src/qemu/qemu_migration.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c index c2570f7303..2bd1a464bf 100644 --- a/src/qemu/qemu_migration.c +++ b/src/qemu/qemu_migration.c @@ -1266,7 +1266,7 @@ qemuMigrationSrcIsSafe(virDomainDefPtr def, virReportError(VIR_ERR_MIGRATE_UNSAFE, "%s", _("Migration may lead to data corruption if disks" - " use cache != none or cache != directsync")); + " use cache other than none or directsync")); return false; } -- 2.22.1
QEMU 4.0.0 and newer automatically drops caches at the end of migration. Let's check for this capability so that we can allow migration when disk cache is turned on. Signed-off-by: Jiri Denemark <jdenemar@redhat.com> --- src/qemu/qemu_capabilities.c | 2 ++ src/qemu/qemu_capabilities.h | 1 + tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml | 1 + tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml | 1 + tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml | 1 + 9 files changed, 10 insertions(+) diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c index 405bc3f288..c9677315ab 100644 --- a/src/qemu/qemu_capabilities.c +++ b/src/qemu/qemu_capabilities.c @@ -536,6 +536,7 @@ VIR_ENUM_IMPL(virQEMUCaps, /* 335 */ "bochs-display", + "migration-file-drop-cache", ); @@ -1279,6 +1280,7 @@ static struct virQEMUCapsStringFlags virQEMUCapsQMPSchemaQueries[] = { { "query-iothreads/ret-type/poll-max-ns", QEMU_CAPS_IOTHREAD_POLLING }, { "query-display-options/ret-type/+egl-headless/rendernode", QEMU_CAPS_EGL_HEADLESS_RENDERNODE }, { "nbd-server-add/arg-type/bitmap", QEMU_CAPS_NBD_BITMAP }, + { "blockdev-add/arg-type/+file/drop-cache", QEMU_CAPS_MIGRATION_FILE_DROP_CACHE }, }; typedef struct _virQEMUCapsObjectTypeProps virQEMUCapsObjectTypeProps; diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h index d7c6df20c7..6db0f28a5f 100644 --- a/src/qemu/qemu_capabilities.h +++ b/src/qemu/qemu_capabilities.h @@ -517,6 +517,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */ /* 335 */ QEMU_CAPS_DEVICE_BOCHS_DISPLAY, /* -device bochs-display */ + QEMU_CAPS_MIGRATION_FILE_DROP_CACHE, /* migration with disk cache on is safe for typ='file' disks */ QEMU_CAPS_LAST /* this must always be the last item */ } virQEMUCapsFlags; diff --git a/tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml b/tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml index 8fe369f518..20f119665b 100644 --- a/tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml +++ b/tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml @@ -164,6 +164,7 @@ <flag name='bitmap-merge'/> <flag name='nbd-bitmap'/> <flag name='bochs-display'/> + <flag name='migration-file-drop-cache'/> <version>4000000</version> <kvmVersion>0</kvmVersion> <microcodeVersion>61700758</microcodeVersion> diff --git a/tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml b/tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml index 2df230c4f7..9ea6f4d046 100644 --- a/tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml +++ b/tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml @@ -169,6 +169,7 @@ <flag name='bitmap-merge'/> <flag name='nbd-bitmap'/> <flag name='bochs-display'/> + <flag name='migration-file-drop-cache'/> <version>4000000</version> <kvmVersion>0</kvmVersion> <microcodeVersion>42900758</microcodeVersion> diff --git a/tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml b/tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml index f4acda457a..7503c2dbcd 100644 --- a/tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml +++ b/tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml @@ -167,6 +167,7 @@ <flag name='bitmap-merge'/> <flag name='nbd-bitmap'/> <flag name='bochs-display'/> + <flag name='migration-file-drop-cache'/> <version>4000000</version> <kvmVersion>0</kvmVersion> <microcodeVersion>0</microcodeVersion> diff --git a/tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml b/tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml index e71d83ee06..4a94179ee7 100644 --- a/tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml +++ b/tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml @@ -167,6 +167,7 @@ <flag name='bitmap-merge'/> <flag name='nbd-bitmap'/> <flag name='bochs-display'/> + <flag name='migration-file-drop-cache'/> <version>4000000</version> <kvmVersion>0</kvmVersion> <microcodeVersion>0</microcodeVersion> diff --git a/tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml b/tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml index a1ac2587a0..ef802f3d1f 100644 --- a/tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml +++ b/tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml @@ -131,6 +131,7 @@ <flag name='query-current-machine'/> <flag name='bitmap-merge'/> <flag name='nbd-bitmap'/> + <flag name='migration-file-drop-cache'/> <version>4000000</version> <kvmVersion>0</kvmVersion> <microcodeVersion>39100758</microcodeVersion> diff --git a/tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml b/tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml index 1d44a5a1ba..87c95f4d18 100644 --- a/tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml +++ b/tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml @@ -206,6 +206,7 @@ <flag name='nbd-bitmap'/> <flag name='x86-max-cpu'/> <flag name='bochs-display'/> + <flag name='migration-file-drop-cache'/> <version>4000000</version> <kvmVersion>0</kvmVersion> <microcodeVersion>43100758</microcodeVersion> diff --git a/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml b/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml index f336aeb48c..f4583d7fe7 100644 --- a/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml +++ b/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml @@ -208,6 +208,7 @@ <flag name='cpu-unavailable-features'/> <flag name='canonical-cpu-features'/> <flag name='bochs-display'/> + <flag name='migration-file-drop-cache'/> <version>4000050</version> <kvmVersion>0</kvmVersion> <microcodeVersion>43100759</microcodeVersion> -- 2.22.1
On 8/13/19 11:08 AM, Jiri Denemark wrote:
QEMU 4.0.0 and newer automatically drops caches at the end of migration. Let's check for this capability so that we can allow migration when disk cache is turned on.
Signed-off-by: Jiri Denemark <jdenemar@redhat.com> --- src/qemu/qemu_capabilities.c | 2 ++
+++ b/src/qemu/qemu_capabilities.h @@ -517,6 +517,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */
/* 335 */ QEMU_CAPS_DEVICE_BOCHS_DISPLAY, /* -device bochs-display */ + QEMU_CAPS_MIGRATION_FILE_DROP_CACHE, /* migration with disk cache on is safe for typ='file' disks */
s/typ/type/ long line, is that a problem? -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
When QEMU supports flushing caches at the end of migration, we can safely allow migration even if disk/driver/@cache is not none nor directsync. Signed-off-by: Jiri Denemark <jdenemar@redhat.com> --- src/qemu/qemu_migration.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c index 2bd1a464bf..bd40a8e70d 100644 --- a/src/qemu/qemu_migration.c +++ b/src/qemu/qemu_migration.c @@ -1214,6 +1214,7 @@ qemuMigrationSrcIsAllowed(virQEMUDriverPtr driver, static bool qemuMigrationSrcIsSafe(virDomainDefPtr def, + virQEMUCapsPtr qemuCaps, size_t nmigrate_disks, const char **migrate_disks, unsigned int flags) @@ -1264,6 +1265,11 @@ qemuMigrationSrcIsSafe(virDomainDefPtr def, disk->cachemode == VIR_DOMAIN_DISK_CACHE_DIRECTSYNC) continue; + if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_MIGRATION_FILE_DROP_CACHE)) { + VIR_DEBUG("QEMU supports flushing caches; migration is safe"); + continue; + } + virReportError(VIR_ERR_MIGRATE_UNSAFE, "%s", _("Migration may lead to data corruption if disks" " use cache other than none or directsync")); @@ -1971,7 +1977,8 @@ qemuMigrationSrcBeginPhase(virQEMUDriverPtr driver, goto cleanup; if (!(flags & (VIR_MIGRATE_UNSAFE | VIR_MIGRATE_OFFLINE)) && - !qemuMigrationSrcIsSafe(vm->def, nmigrate_disks, migrate_disks, flags)) + !qemuMigrationSrcIsSafe(vm->def, priv->qemuCaps, + nmigrate_disks, migrate_disks, flags)) goto cleanup; if (flags & VIR_MIGRATE_POSTCOPY && @@ -4583,7 +4590,8 @@ qemuMigrationSrcPerformJob(virQEMUDriverPtr driver, goto endjob; if (!(flags & (VIR_MIGRATE_UNSAFE | VIR_MIGRATE_OFFLINE)) && - !qemuMigrationSrcIsSafe(vm->def, nmigrate_disks, migrate_disks, flags)) + !qemuMigrationSrcIsSafe(vm->def, priv->qemuCaps, + nmigrate_disks, migrate_disks, flags)) goto endjob; qemuMigrationSrcStoreDomainState(vm); -- 2.22.1
On Tue, Aug 13, 2019 at 18:08:35 +0200, Jiri Denemark wrote:
QEMU 4.0.0 and newer automatically drops caches at the end of migration, which means we can safely allow migration even if disk/driver/@cache is not none nor directsync.
Jiri Denemark (3): qemu: Clarify error message in qemuMigrationSrcIsSafe qemu: Check for drop-cache capability qemu: Allow migration with disk cache on
ACK series.
participants (3)
-
Eric Blake -
Jiri Denemark -
Peter Krempa