[Qemu-devel] [PATCH v12 24/36] cpu: Convert CpuInfo into flat union

[Eric Blake <eblake@redhat.com>]

The CpuInfo struct is used only by the 'query-cpus' output
command, so we are free to modify it by adding fields (clients
are already supposed to ignore unknown output fields), or by
changing optional members to mandatory, while still keeping
QMP wire compatibility with older versions of qemu.

When qapi type CpuInfo was originally created for 0.14, we had
no notion of a flat union, and instead just listed a bunch of
optional fields with documentation about the mutually-exclusive
choice of which instruction pointer field(s) would be provided
for a given architecture.  But now that we have flat unions and
introspection, it is better to segregate off which fields will
be provided according to the actual architecture.  With this in
place, we no longer need the fields to be optional, because the
choice of the new 'arch' discriminator serves that role.

This has an additional benefit: the old all-in-one struct was
the only place in the code base that had a case-sensitive
naming of members 'pc' vs. 'PC'.  Separating these spellings
into different branches of the flat union will allow us to add
restrictions against future case-insensitive collisions, since
that is generally a poor interface practice.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v12: s/2.5/2.6/, typo fix
v11: also fix qmp-commands.hx, improve commit message. If this
misses 2.5 (likely), it will need updates to call out 2.6
v10: new patch
---
 cpus.c           |  31 ++++++++------
 hmp.c            |  30 +++++++++-----
 qapi-schema.json | 120 ++++++++++++++++++++++++++++++++++++++++++++++---------
 qmp-commands.hx  |   4 ++
 4 files changed, 143 insertions(+), 42 deletions(-)

diff --git a/cpus.c b/cpus.c
index 877bd70..77ba15b 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1556,22 +1556,29 @@ CpuInfoList *qmp_query_cpus(Error **errp)
         info->value->qom_path = object_get_canonical_path(OBJECT(cpu));
         info->value->thread_id = cpu->thread_id;
 #if defined(TARGET_I386)
-        info->value->has_pc = true;
-        info->value->pc = env->eip + env->segs[R_CS].base;
+        info->value->arch = CPU_INFO_ARCH_X86;
+        info->value->u.x86 = g_new0(CpuInfoX86, 1);
+        info->value->u.x86->pc = env->eip + env->segs[R_CS].base;
 #elif defined(TARGET_PPC)
-        info->value->has_nip = true;
-        info->value->nip = env->nip;
+        info->value->arch = CPU_INFO_ARCH_PPC;
+        info->value->u.ppc = g_new0(CpuInfoPpc, 1);
+        info->value->u.ppc->nip = env->nip;
 #elif defined(TARGET_SPARC)
-        info->value->has_pc = true;
-        info->value->pc = env->pc;
-        info->value->has_npc = true;
-        info->value->npc = env->npc;
+        info->value->arch = CPU_INFO_ARCH_SPARC;
+        info->value->u.sparc = g_new0(CpuInfoSPARC, 1);
+        info->value->u.sparc->pc = env->pc;
+        info->value->u.sparc->npc = env->npc;
 #elif defined(TARGET_MIPS)
-        info->value->has_PC = true;
-        info->value->PC = env->active_tc.PC;
+        info->value->arch = CPU_INFO_ARCH_MIPS;
+        info->value->u.mips = g_new0(CpuInfoMips, 1);
+        info->value->u.mips->PC = env->active_tc.PC;
 #elif defined(TARGET_TRICORE)
-        info->value->has_PC = true;
-        info->value->PC = env->PC;
+        info->value->arch = CPU_INFO_ARCH_TRICORE;
+        info->value->u.tricore = g_new0(CpuInfoTricore, 1);
+        info->value->u.tricore->PC = env->PC;
+#else
+        info->value->arch = CPU_INFO_ARCH_OTHER;
+        info->value->u.other = g_new0(CpuInfoOther, 1);
 #endif

         /* XXX: waiting for the qapi to support GSList */
diff --git a/hmp.c b/hmp.c
index 1b402c4..c2b2c16 100644
--- a/hmp.c
+++ b/hmp.c
@@ -311,17 +311,25 @@ void hmp_info_cpus(Monitor *mon, const QDict *qdict)

         monitor_printf(mon, "%c CPU #%" PRId64 ":", active, cpu->value->CPU);

-        if (cpu->value->has_pc) {
-            monitor_printf(mon, " pc=0x%016" PRIx64, cpu->value->pc);
-        }
-        if (cpu->value->has_nip) {
-            monitor_printf(mon, " nip=0x%016" PRIx64, cpu->value->nip);
-        }
-        if (cpu->value->has_npc) {
-            monitor_printf(mon, " npc=0x%016" PRIx64, cpu->value->npc);
-        }
-        if (cpu->value->has_PC) {
-            monitor_printf(mon, " PC=0x%016" PRIx64, cpu->value->PC);
+        switch (cpu->value->arch) {
+        case CPU_INFO_ARCH_X86:
+            monitor_printf(mon, " pc=0x%016" PRIx64, cpu->value->u.x86->pc);
+            break;
+        case CPU_INFO_ARCH_PPC:
+            monitor_printf(mon, " nip=0x%016" PRIx64, cpu->value->u.ppc->nip);
+            break;
+        case CPU_INFO_ARCH_SPARC:
+            monitor_printf(mon, " pc=0x%016" PRIx64, cpu->value->u.sparc->pc);
+            monitor_printf(mon, " npc=0x%016" PRIx64, cpu->value->u.sparc->npc);
+            break;
+        case CPU_INFO_ARCH_MIPS:
+            monitor_printf(mon, " PC=0x%016" PRIx64, cpu->value->u.mips->PC);
+            break;
+        case CPU_INFO_ARCH_TRICORE:
+            monitor_printf(mon, " PC=0x%016" PRIx64, cpu->value->u.tricore->PC);
+            break;
+        default:
+            break;
         }

         if (cpu->value->halted) {
diff --git a/qapi-schema.json b/qapi-schema.json
index 8b1a423..67e80a5 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -744,43 +744,125 @@
 { 'command': 'query-mice', 'returns': ['MouseInfo'] }

 ##
-# @CpuInfo:
+# @CpuInfoArch:
 #
-# Information about a virtual CPU
+# An enumeration of cpu types that enable additional information during
+# @query-cpus.
+#
+# Since: 2.6
+##
+{ 'enum': 'CpuInfoArch',
+  'data': ['x86', 'sparc', 'ppc', 'mips', 'tricore', 'other' ] }
+
+##
+# @CpuInfoBase:
+#
+# Common information about a virtual CPU
 #
 # @CPU: the index of the virtual CPU
 #
-# @current: this only exists for backwards compatible and should be ignored
+# @current: this only exists for backwards compatibility and should be ignored
 #
 # @halted: true if the virtual CPU is in the halt state.  Halt usually refers
 #          to a processor specific low power mode.
 #
 # @qom_path: path to the CPU object in the QOM tree (since 2.4)
 #
-# @pc: #optional If the target is i386 or x86_64, this is the 64-bit instruction
-#                pointer.
-#                If the target is Sparc, this is the PC component of the
-#                instruction pointer.
-#
-# @nip: #optional If the target is PPC, the instruction pointer
-#
-# @npc: #optional If the target is Sparc, the NPC component of the instruction
-#                 pointer
-#
-# @PC: #optional If the target is MIPS, the instruction pointer
-#
 # @thread_id: ID of the underlying host thread
 #
+# @arch: architecture of the cpu, which determines which additional fields
+#        will be listed (since 2.6)
+#
 # Since: 0.14.0
 #
 # Notes: @halted is a transient state that changes frequently.  By the time the
 #        data is sent to the client, the guest may no longer be halted.
 ##
-{ 'struct': 'CpuInfo',
+{ 'struct': 'CpuInfoBase',
   'data': {'CPU': 'int', 'current': 'bool', 'halted': 'bool',
-           'qom_path': 'str',
-           '*pc': 'int', '*nip': 'int', '*npc': 'int', '*PC': 'int',
-           'thread_id': 'int'} }
+           'qom_path': 'str', 'thread_id': 'int', 'arch': 'CpuInfoArch' } }
+
+##
+# @CpuInfo:
+#
+# Information about a virtual CPU
+#
+# Since: 0.14.0
+##
+{ 'union': 'CpuInfo', 'base': 'CpuInfoBase', 'discriminator': 'arch',
+  'data': { 'x86': 'CpuInfoX86',
+            'sparc': 'CpuInfoSparc',
+            'ppc': 'CpuInfoPpc',
+            'mips': 'CpuInfoMips',
+            'tricore': 'CpuInfoTricore',
+            'other': 'CpuInfoOther' } }
+
+##
+# @CpuInfoX86:
+#
+# Additional information about a virtual i386 or x86_64 CPU
+#
+# @pc: the 64-bit instruction pointer
+#
+# Since 2.6
+##
+{ 'struct': 'CpuInfoX86', 'data': { 'pc': 'int' } }
+
+##
+# @CpuInfoSparc:
+#
+# Additional information about a virtual Sparc CPU
+#
+# @pc: the PC component of the instruction pointer
+#
+# @npc: the NPC component of the instruction pointer
+#
+# Since 2.6
+##
+{ 'struct': 'CpuInfoSparc', 'data': { 'pc': 'int', 'npc': 'int' } }
+
+##
+# @CpuInfoPpc:
+#
+# Additional information about a virtual PPC CPU
+#
+# @nip: the instruction pointer
+#
+# Since 2.6
+##
+{ 'struct': 'CpuInfoPpc', 'data': { 'nip': 'int' } }
+
+##
+# @CpuInfoMips:
+#
+# Additional information about a virtual MIPS CPU
+#
+# @PC: the instruction pointer
+#
+# Since 2.6
+##
+{ 'struct': 'CpuInfoMips', 'data': { 'PC': 'int' } }
+
+##
+# @CpuInfoTricore:
+#
+# Additional information about a virtual Tricore CPU
+#
+# @PC: the instruction pointer
+#
+# Since 2.6
+##
+{ 'struct': 'CpuInfoTricore', 'data': { 'PC': 'int' } }
+
+##
+# @CpuInfoOther:
+#
+# No additional information is available about the virtual CPU
+#
+# Since 2.6
+#
+##
+{ 'struct': 'CpuInfoOther', 'data': { } }

 ##
 # @query-cpus:
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 9d8b42f..1b5ecb3 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2765,6 +2765,8 @@ Return a json-array. Each CPU is represented by a json-object, which contains:
 - "current": true if this is the current CPU, false otherwise (json-bool)
 - "halted": true if the cpu is halted, false otherwise (json-bool)
 - "qom_path": path to the CPU object in the QOM tree (json-str)
+- "arch": architecture of the cpu, which determines what additional
+          keys will be present (json-str)
 - Current program counter. The key's name depends on the architecture:
      "pc": i386/x86_64 (json-int)
      "nip": PPC (json-int)
@@ -2782,6 +2784,7 @@ Example:
             "current":true,
             "halted":false,
             "qom_path":"/machine/unattached/device[0]",
+            "arch":"x86",
             "pc":3227107138,
             "thread_id":3134
          },
@@ -2790,6 +2793,7 @@ Example:
             "current":false,
             "halted":true,
             "qom_path":"/machine/unattached/device[2]",
+            "arch":"x86",
             "pc":7108165,
             "thread_id":3135
          }
-- 
2.4.3