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[Qemu-devel] [PATCH v3 2/2] qemu-ga: add guest-set-support-level command


From: Michael Roth
Subject: [Qemu-devel] [PATCH v3 2/2] qemu-ga: add guest-set-support-level command
Date: Mon, 16 Jan 2012 18:13:59 -0600

Recently commands where introduced on the mailing that involved adding
commands to the guest agent that could potentially break older versions
of QEMU. While it's okay to expect that qemu-ga can be updated to support
newer host features, it's unrealistic to require a host to be updated to
support qemu-ga features, or to expect that qemu-ga should be downgraded
in these circumstances, especially considering that a large mix of
guests/agents may be running on a particular host.

To address this, we introduce here a mechanism to set qemu-ga's
feature-set to one that is known to be compatible with
the host/QEMU running the guest. As new commands/options are added, we
can maintain backward-compatibility by adding conditional checks to filter
out host-incompatible functionality based on the host-specified support
level (generally analogous to the host QEMU version) set by the
client.

The current default/minimum support level supports all versions of QEMU
that have had qemu-ga in-tree (0.15.0, 1.0.0) and so should be
backward-compatible with existing hosts/clients.

Signed-off-by: Michael Roth <address@hidden>
---
 qapi-schema-guest.json     |   67 +++++++++++++++++++++++++++++++++++++++++++-
 qemu-ga.c                  |   46 ++++++++++++++++++++++++++++++
 qga/guest-agent-commands.c |   13 ++++++++
 qga/guest-agent-core.h     |   11 +++++++
 4 files changed, 136 insertions(+), 1 deletions(-)

diff --git a/qapi-schema-guest.json b/qapi-schema-guest.json
index 2d4917e..2e3d480 100644
--- a/qapi-schema-guest.json
+++ b/qapi-schema-guest.json
@@ -51,6 +51,27 @@
   'data': { 'name': 'str', 'enabled': 'bool' } }
 
 ##
+# @GuestAgentSupportLevel
+#
+# Guest agent support/compatability level (as configured by
+# guest agent defaults of get-set-support-level command)
+#
+# Three numerical fields describe the support level:
+#
+# <major>.<minor>.<micro>
+#
+# @major: As above
+#
+# @minor: As above
+#
+# @micro: As above
+#
+# Since 1.1.0
+##
+{ 'type': 'GuestAgentSupportLevel',
+  'data': { 'major': 'int', 'minor': 'int', 'micro': 'int' } }
+
+##
 # @GuestAgentInfo
 #
 # Information about guest agent.
@@ -59,11 +80,17 @@
 #
 # @supported_commands: Information about guest agent commands
 #
+# @support_level: Current support/compatability level, as set by
+#                 guest agent defaults or guest-set-support-level
+#                 command.
+#
 # Since 0.15.0
 ##
 { 'type': 'GuestAgentInfo',
   'data': { 'version': 'str',
-            'supported_commands': ['GuestAgentCommandInfo'] } }
+            'supported_commands': ['GuestAgentCommandInfo']
+            'support_level': 'GuestAgentSupportLevel' } }
+
 ##
 # @guest-info:
 #
@@ -77,6 +104,44 @@
   'returns': 'GuestAgentInfo' }
 
 ##
+# @guest-set-support-level:
+#
+# Set guest agent feature-set to one that is compatible with/supported by
+# the host.
+#
+# Certain commands/options may have dependencies on host
+# version/support-level, such as specific QEMU features (such
+# dependencies will be noted in this schema). By default we assume 1.0.0,
+# which is backward-compatible with QEMU 0.15.0/1.0, and should be compatible
+# with later versions of QEMU as well. To enable newer guest agent features,
+# this command must be issued to raise the support-level to one corresponding
+# to supported host QEMU/KVM/etc capabilities.
+#
+# The host support-level is generally <= host QEMU version
+# level. Note that undefined behavior may occur if a support-level is
+# provided that exceeds the capabilities of the version of QEMU currently
+# running the guest. Any level specified below 1.0.0 will default to 1.0.0.
+#
+# The currently set support level is obtainable via the guest-info command.
+#
+# Three numerical fields describe the host support/compatability level:
+#
+# <major>.<minor>.<micro>
+#
+# @major: As above
+#
+# @minor: As above
+#
+# @micro: As above
+#
+# Returns: Nothing on success
+#
+# Since: 1.1.0
+##
+{ 'command': 'guest-set-support-level',
+  'data':    { 'major': 'int', 'minor': 'int', '*micro': 'int' } }
+
+##
 # @guest-shutdown:
 #
 # Initiate guest-activated shutdown. Note: this is an asynchronous
diff --git a/qemu-ga.c b/qemu-ga.c
index 29e4f64..8e5b075 100644
--- a/qemu-ga.c
+++ b/qemu-ga.c
@@ -28,6 +28,7 @@
 #include "qerror.h"
 #include "error_int.h"
 #include "qapi/qmp-core.h"
+#include "qga-qapi-types.h"
 
 #define QGA_VIRTIO_PATH_DEFAULT "/dev/virtio-ports/org.qemu.guest_agent.0"
 #define QGA_PIDFILE_DEFAULT "/var/run/qemu-ga.pid"
@@ -102,6 +103,45 @@ static void usage(const char *cmd)
 
 static void conn_channel_close(GAState *s);
 
+static GuestAgentSupportLevel ga_support_level;
+
+static int ga_cmp_support_levels(GuestAgentSupportLevel a,
+                                 GuestAgentSupportLevel b)
+{
+    if (a.major == b.major) {
+        if (a.minor == b.minor) {
+            return a.micro - b.micro;
+        }
+        return a.minor - b.minor;
+    }
+    return a.major - b.major;
+}
+
+bool ga_has_support_level(int major, int minor, int micro)
+{
+    const GuestAgentSupportLevel level = { major, minor, micro };
+    return ga_cmp_support_levels(ga_support_level, level) >= 0;
+}
+
+void ga_set_support_level(GuestAgentSupportLevel level)
+{
+    const GuestAgentSupportLevel min_support_level = {
+        QGA_SUPPORT_LEVEL_MAJOR_MIN,
+        QGA_SUPPORT_LEVEL_MINOR_MIN,
+        QGA_SUPPORT_LEVEL_MICRO_MIN
+    };
+    if (ga_cmp_support_levels(level, min_support_level) <= 0) {
+        ga_support_level = min_support_level;
+    } else {
+        ga_support_level = level;
+    }
+}
+
+GuestAgentSupportLevel ga_get_support_level(void)
+{
+    return ga_support_level;
+}
+
 static const char *ga_log_level_str(GLogLevelFlags level)
 {
     switch (level & G_LOG_LEVEL_MASK) {
@@ -569,6 +609,11 @@ int main(int argc, char **argv)
     GLogLevelFlags log_level = G_LOG_LEVEL_ERROR | G_LOG_LEVEL_CRITICAL;
     FILE *log_file = stderr;
     GAState *s;
+    const GuestAgentSupportLevel default_support_level = {
+        QGA_SUPPORT_LEVEL_MAJOR_DEFAULT,
+        QGA_SUPPORT_LEVEL_MINOR_DEFAULT,
+        QGA_SUPPORT_LEVEL_MICRO_DEFAULT
+    };
 
     module_call_init(MODULE_INIT_QAPI);
 
@@ -642,6 +687,7 @@ int main(int argc, char **argv)
         become_daemon(pidfile);
     }
 
+    ga_set_support_level(default_support_level);
     s = g_malloc0(sizeof(GAState));
     s->conn_channel = NULL;
     s->path = path;
diff --git a/qga/guest-agent-commands.c b/qga/guest-agent-commands.c
index a09c8ca..656dde8 100644
--- a/qga/guest-agent-commands.c
+++ b/qga/guest-agent-commands.c
@@ -62,6 +62,8 @@ struct GuestAgentInfo *qmp_guest_info(Error **err)
     char **cmd_list_head, **cmd_list;
 
     info->version = g_strdup(QGA_VERSION);
+    info->support_level = g_malloc0(sizeof(GuestAgentSupportLevel));
+    *info->support_level = ga_get_support_level();
 
     cmd_list_head = cmd_list = qmp_get_command_list();
     if (*cmd_list_head == NULL) {
@@ -87,6 +89,17 @@ out:
     return info;
 }
 
+void qmp_guest_set_support_level(int64_t major, int64_t minor, bool has_micro,
+                                 int64_t micro, Error **errp)
+{
+    GuestAgentSupportLevel level = {
+        major,
+        minor,
+        has_micro ? micro : 0
+    };
+    ga_set_support_level(level);
+}
+
 void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
 {
     int ret;
diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h
index e42b91d..7327e73 100644
--- a/qga/guest-agent-core.h
+++ b/qga/guest-agent-core.h
@@ -12,8 +12,16 @@
  */
 #include "qapi/qmp-core.h"
 #include "qemu-common.h"
+#include "qga-qapi-types.h"
 
 #define QGA_VERSION "1.0"
+#define QGA_SUPPORT_LEVEL_MAJOR_DEFAULT 1
+#define QGA_SUPPORT_LEVEL_MINOR_DEFAULT 0
+#define QGA_SUPPORT_LEVEL_MICRO_DEFAULT 0
+/* lowest possible support level */
+#define QGA_SUPPORT_LEVEL_MAJOR_MIN 1
+#define QGA_SUPPORT_LEVEL_MINOR_MIN 0
+#define QGA_SUPPORT_LEVEL_MICRO_MIN 0
 #define QGA_READ_COUNT_DEFAULT 4 << 10
 
 typedef struct GAState GAState;
@@ -29,3 +37,6 @@ GACommandState *ga_command_state_new(void);
 bool ga_logging_enabled(GAState *s);
 void ga_disable_logging(GAState *s);
 void ga_enable_logging(GAState *s);
+bool ga_has_support_level(int major, int minor, int micro);
+void ga_set_support_level(GuestAgentSupportLevel level);
+GuestAgentSupportLevel ga_get_support_level(void);
-- 
1.7.4.1




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