[Qemu-devel] [PATCH 16/16] add cpu-add qmp command and implement CPU hot-add for target-i386

[Igor Mammedov <imammedo@redhat.com>]

... via current_machine->cpu_hot_add() hook called by cpu-set QMP command,
for x86 target.

cpu-add's "id" argument is a CPU thread number in a range [0..max-cpus - 1)

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
v5:
  * accept id=[0..max_cpus) range in cpu-add command
v4:
  * merge "qmp: add cpu-add qmp command" & "target-i386: implement CPU hot-add" patches
  * move notifier call to CPUCLass.realize()
  * add hook cpu_hot_add to QEMUMachine
  * make QEMUMachineInitArgs global and keep default cpu_model there

v3:
  * it appears that 'online/offline' in cpu-set are confusing people
    with what command actually does and users might have to distinguish
    if 'offline' is not implemented by parsing error message. To simplify
    things replace cpu-set with cpu-add command to show more clear what
    command does and just add cpu-del when CPU remove is implemented.

v2:
  * s/cpu_set/cpu-set/
  * qmp doc style fix
  * use bool type instead of opencodding online/offline string
     suggested-by: Eric Blake <eblake@redhat.com>
---
 hw/i386/pc.c        | 22 ++++++++++++++++++++++
 include/hw/boards.h |  3 +++
 qapi-schema.json    | 11 +++++++++++
 qmp-commands.hx     | 23 +++++++++++++++++++++++
 qmp.c               | 10 ++++++++++
 vl.c                |  6 +++++-
 6 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index a5c19a2..f09e44b 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -53,6 +53,7 @@
 #include "qemu/bitmap.h"
 #include "qemu/config-file.h"
 #include "hw/i386/icc_bus.h"
+#include "hw/boards.h"
 
 /* debug PC/ISA interrupts */
 //#define DEBUG_IRQ
@@ -911,6 +912,25 @@ static X86CPU *pc_new_cpu(const char *cpu_model, int64_t apic_id, Error **errp)
     return cpu;
 }
 
+static void do_cpu_hot_add(const int64_t id, Error **errp)
+{
+    int64_t apic_id = x86_cpu_apic_id_from_index(id);
+
+    if (cpu_exists(apic_id)) {
+        error_setg(errp, "Unable to add CPU: %" PRIi64
+                   ", it already exists", id);
+        return;
+    }
+
+    if (id >= max_cpus) {
+        error_setg(errp, "Unable to add CPU: %" PRIi64
+                   ", max allowed: %d", id, max_cpus - 1);
+        return;
+    }
+
+    pc_new_cpu(machine_args->cpu_model, apic_id, errp);
+}
+
 void pc_cpus_init(const char *cpu_model)
 {
     int i;
@@ -925,7 +945,9 @@ void pc_cpus_init(const char *cpu_model)
 #else
         cpu_model = "qemu32";
 #endif
+        machine_args->cpu_model = cpu_model;
     }
+    current_machine->hot_add_cpu = do_cpu_hot_add;
 
     ib = SYS_BUS_DEVICE(object_resolve_path_type("icc-bridge",
                                                  TYPE_ICC_BRIDGE, NULL));
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 425bdc7..de8f92a 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -18,6 +18,8 @@ typedef struct QEMUMachineInitArgs {
     const char *cpu_model;
 } QEMUMachineInitArgs;
 
+extern QEMUMachineInitArgs *machine_args;
+
 typedef void QEMUMachineInitFunc(QEMUMachineInitArgs *args);
 
 typedef void QEMUMachineResetFunc(void);
@@ -43,6 +45,7 @@ typedef struct QEMUMachine {
     GlobalProperty *compat_props;
     struct QEMUMachine *next;
     const char *hw_version;
+    void (*hot_add_cpu)(const int64_t id, Error **errp);
 } QEMUMachine;
 
 int qemu_register_machine(QEMUMachine *m);
diff --git a/qapi-schema.json b/qapi-schema.json
index 751d3c2..34d3e84 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1387,6 +1387,17 @@
 { 'command': 'cpu', 'data': {'index': 'int'} }
 
 ##
+# @cpu-add
+#
+# Adds CPU with specified id
+#
+# @id: cpu id of CPU to be created
+#
+# Returns: Nothing on success
+##
+{ 'command': 'cpu-add', 'data': {'id': 'int'} }
+
+##
 # @memsave:
 #
 # Save a portion of guest memory to a file.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 4d65422..1e5d299 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -385,6 +385,29 @@ Note: CPUs' indexes are obtained with the 'query-cpus' command.
 EQMP
 
     {
+        .name       = "cpu-add",
+        .args_type  = "id:i",
+        .mhandler.cmd_new = qmp_marshal_input_cpu_add,
+    },
+
+SQMP
+cpu-add
+-------
+
+Adds virtual cpu
+
+Arguments:
+
+- "id": cpu id (json-int)
+
+Example:
+
+-> { "execute": "cpu-add", "arguments": { "id": 2 } }
+<- { "return": {} }
+
+EQMP
+
+    {
         .name       = "memsave",
         .args_type  = "val:l,size:i,filename:s,cpu:i?",
         .mhandler.cmd_new = qmp_marshal_input_memsave,
diff --git a/qmp.c b/qmp.c
index 55b056b..8a9fd9e 100644
--- a/qmp.c
+++ b/qmp.c
@@ -24,6 +24,7 @@
 #include "hw/qdev.h"
 #include "sysemu/blockdev.h"
 #include "qom/qom-qobject.h"
+#include "hw/boards.h"
 
 NameInfo *qmp_query_name(Error **errp)
 {
@@ -108,6 +109,15 @@ void qmp_cpu(int64_t index, Error **errp)
     /* Just do nothing */
 }
 
+void qmp_cpu_add(int64_t id, Error **errp)
+{
+    if (current_machine->hot_add_cpu) {
+        current_machine->hot_add_cpu(id, errp);
+    } else {
+        error_setg(errp, "Not supported");
+    }
+}
+
 #ifndef CONFIG_VNC
 /* If VNC support is enabled, the "true" query-vnc command is
    defined in the VNC subsystem */
diff --git a/vl.c b/vl.c
index bc9c016..8d87d97 100644
--- a/vl.c
+++ b/vl.c
@@ -179,6 +179,8 @@ int main(int argc, char **argv)
 #define MAX_VIRTIO_CONSOLES 1
 #define MAX_SCLP_CONSOLES 1
 
+QEMUMachineInitArgs *machine_args;
+
 static const char *data_dir[16];
 static int data_dir_idx;
 const char *bios_name = NULL;
@@ -4306,13 +4308,15 @@ int main(int argc, char **argv, char **envp)
                                  .kernel_cmdline = kernel_cmdline,
                                  .initrd_filename = initrd_filename,
                                  .cpu_model = cpu_model };
+    machine_args = &args;
+    current_machine = machine;
+
     machine->init(&args);
 
     cpu_synchronize_all_post_init();
 
     set_numa_modes();
 
-    current_machine = machine;
 
     /* init USB devices */
     if (usb_enabled(false)) {
-- 
1.8.2