On 06.10.25 16:23, Markus Armbruster wrote:
Vladimir Sementsov-Ogievskiy <[email protected]> writes:
To migrate virtio-net TAP device backend (including open fds) locally,
user should simply set migration parameter
backend-transfer = ["virtio-net-tap"]
Why not simple boolean? To simplify migration to further versions,
when more devices will support backend-transfer migration.
Alternatively, we may add per-device option to disable backend-transfer
migration, but still:
1. It's more comfortable to set same capabilities/parameters on both
source and target QEMU, than care about each device.
2. To not break the design, that machine-type + device options +
migration capabilities and parameters are fully define the resulting
migration stream. We'll break this if add in future more
backend-transfer support in devices under same backend-transfer=true
parameter.
Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
---
include/qapi/util.h | 17 ++++++++++++++++
migration/options.c | 32 ++++++++++++++++++++++++++++++
migration/options.h | 2 ++
qapi/migration.json | 47 ++++++++++++++++++++++++++++++++++++---------
4 files changed, 89 insertions(+), 9 deletions(-)
diff --git a/include/qapi/util.h b/include/qapi/util.h
index 29bc4eb865..b953402416 100644
--- a/include/qapi/util.h
+++ b/include/qapi/util.h
@@ -69,4 +69,21 @@ int parse_qapi_name(const char *name, bool complete);
_len; \
})
+/*
+ * For any GenericList @list, return true if it contains specified
+ * element.
+ */
+#define QAPI_LIST_CONTAINS(list, el) \
+ ({ \
+ bool _found = false; \
+ typeof_strip_qual(list) _tail; \
+ for (_tail = list; _tail != NULL; _tail = _tail->next) { \
+ if (_tail->value == el) { \
+ _found = true; \
+ break; \
+ } \
+ } \
+ _found; \
+ })
+
Not a fan of lengthy macros.
There's a single use below: migrate_virtio_net_tap(). I can't see
potential uses for such a search in existing code.
Open-code it in migrate_virtio_net_tap()?
Ok, not a problem
#endif
diff --git a/migration/options.c b/migration/options.c
index 4e923a2e07..137ca2147e 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -13,6 +13,7 @@
#include "qemu/osdep.h"
#include "qemu/error-report.h"
+#include "qapi/util.h"
#include "exec/target_page.h"
#include "qapi/clone-visitor.h"
#include "qapi/error.h"
@@ -262,6 +263,14 @@ bool migrate_mapped_ram(void)
return s->capabilities[MIGRATION_CAPABILITY_MAPPED_RAM];
}
+bool migrate_virtio_net_tap(void)
+{
+ MigrationState *s = migrate_get_current();
+
+ return QAPI_LIST_CONTAINS(s->parameters.backend_transfer,
+ BACKEND_TRANSFER_VIRTIO_NET_TAP);
+}
+
bool migrate_ignore_shared(void)
{
MigrationState *s = migrate_get_current();
@@ -960,6 +969,12 @@ MigrationParameters *qmp_query_migrate_parameters(Error
**errp)
params->has_direct_io = true;
params->direct_io = s->parameters.direct_io;
+ if (s->parameters.backend_transfer) {
+ params->has_backend_transfer = true;
+ params->backend_transfer = QAPI_CLONE(BackendTransferList,
+ s->parameters.backend_transfer);
+ }
+
return params;
}
@@ -993,6 +1008,7 @@ void migrate_params_init(MigrationParameters *params)
params->has_mode = true;
params->has_zero_page_detection = true;
params->has_direct_io = true;
+ params->has_backend_transfer = true;
}
/*
@@ -1179,6 +1195,11 @@ bool migrate_params_check(MigrationParameters *params,
Error **errp)
return false;
}
+ if (params->has_backend_transfer) {
+ error_setg(errp, "Not implemented");
+ return false;
+ }
+
This goes away in the next patch. Fine, but mentioning the gap in the
commit message can save reviewer a bit of work.
Right :(
return true;
}
@@ -1297,6 +1318,10 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
if (params->has_direct_io) {
dest->direct_io = params->direct_io;
}
+
+ if (params->has_backend_transfer) {
+ dest->backend_transfer = params->backend_transfer;
+ }
}
static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1429,6 +1454,13 @@ static void migrate_params_apply(MigrateSetParameters
*params, Error **errp)
if (params->has_direct_io) {
s->parameters.direct_io = params->direct_io;
}
+
+ if (params->has_backend_transfer) {
+ qapi_free_BackendTransferList(s->parameters.backend_transfer);
+
+ s->parameters.backend_transfer = QAPI_CLONE(BackendTransferList,
+ params->backend_transfer);
+ }
}
void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
diff --git a/migration/options.h b/migration/options.h
index 82d839709e..55c0345433 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -87,6 +87,8 @@ const char *migrate_tls_hostname(void);
uint64_t migrate_xbzrle_cache_size(void);
ZeroPageDetection migrate_zero_page_detection(void);
+bool migrate_virtio_net_tap(void);
+
/* parameters helpers */
bool migrate_params_check(MigrationParameters *params, Error **errp);
diff --git a/qapi/migration.json b/qapi/migration.json
index 2387c21e9c..e39785dc07 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -747,6 +747,18 @@
'*transform': 'BitmapMigrationBitmapAliasTransform'
} }
+##
+# @BackendTransfer:
+#
+# @virtio-net-tap: Enable backend-transfer migration for virtio-net/tap. When
+# enabled, TAP fds and all related state is passed to target QEMU through
+# migration channel (which should be unix socket).
Suggest "are passed to the destination in the migration channel" and
"should be a UNIX domain socket".
docs/devel/qapi-code-gen.rst:
For legibility, wrap text paragraphs so every line is at most 70
characters long.
Separate sentences with two spaces.
Ok. We do lack this check in checkpatch
+#
+# Since: 10.2
+##
+{ 'enum': 'BackendTransfer',
+ 'data': [ 'virtio-net-tap' ] }
+
##
# @BitmapMigrationNodeAlias:
#
@@ -924,10 +936,14 @@
# only has effect if the @mapped-ram capability is enabled.
# (Since 9.1)
#
+# @backend-transfer: List of targets to enable backend-transfer
+# migration for. This requires migration channel to be a unix
+# socket (to pass fds through). (Since 10.2)
Elsewhere, we describe the same restriction like this:
This CPR channel must support
# file descriptor transfer with SCM_RIGHTS, i.e. it must be a
# UNIX domain socket.
Thanks, I'll copy this phrasing to be consistent.
+#
# Features:
#
-# @unstable: Members @x-checkpoint-delay and
-# @x-vcpu-dirty-limit-period are experimental.
+# @unstable: Members @x-checkpoint-delay,
+# @x-vcpu-dirty-limit-period and @backend-transfer are experimental.
List members in alphabetical order, please.
#
# Since: 2.4
##
@@ -950,7 +966,8 @@
'vcpu-dirty-limit',
'mode',
'zero-page-detection',
- 'direct-io'] }
+ 'direct-io',
+ 'backend-transfer' ] }
Forgot feature 'unstable'?
Opps. Interesting, how it compiles? Usually, inconsistencies between
QAPI comments and definitions are hardly checked.
##
# @MigrateSetParameters:
@@ -1105,10 +1122,14 @@
# only has effect if the @mapped-ram capability is enabled.
# (Since 9.1)
#
+# @backend-transfer: List of targets to enable backend-transfer
+# migration for. This requires migration channel to be a unix
+# socket (to pass fds through). (Since 10.2)
+#
# Features:
#
-# @unstable: Members @x-checkpoint-delay and
-# @x-vcpu-dirty-limit-period are experimental.
+# @unstable: Members @x-checkpoint-delay,
+# @x-vcpu-dirty-limit-period and @backend-transfer are experimental.
#
# TODO: either fuse back into `MigrationParameters`, or make
# `MigrationParameters` members mandatory
@@ -1146,7 +1167,9 @@
'*vcpu-dirty-limit': 'uint64',
'*mode': 'MigMode',
'*zero-page-detection': 'ZeroPageDetection',
- '*direct-io': 'bool' } }
+ '*direct-io': 'bool',
+ '*backend-transfer': { 'type': [ 'BackendTransfer' ],
+ 'features': [ 'unstable' ] } } }
##
# @migrate-set-parameters:
@@ -1315,10 +1338,14 @@
# only has effect if the @mapped-ram capability is enabled.
# (Since 9.1)
#
+# @backend-transfer: List of targets to enable backend-transfer
+# migration for. This requires migration channel to be a unix
+# socket (to pass fds through). (Since 10.2)
+#
# Features:
#
-# @unstable: Members @x-checkpoint-delay and
-# @x-vcpu-dirty-limit-period are experimental.
+# @unstable: Members @x-checkpoint-delay,
+# @x-vcpu-dirty-limit-period and @backend-transfer are experimental.
#
# Since: 2.4
##
@@ -1353,7 +1380,9 @@
'*vcpu-dirty-limit': 'uint64',
'*mode': 'MigMode',
'*zero-page-detection': 'ZeroPageDetection',
- '*direct-io': 'bool' } }
+ '*direct-io': 'bool',
+ '*backend-transfer': { 'type': [ 'BackendTransfer' ],
+ 'features': [ 'unstable' ] } } }
##
# @query-migrate-parameters:
Thanks for reviewing, I'll fix all notes in v7.
--
Best regards,
Vladimir
