[PATCH v3] qga: Correct loop count in qmp_guest_get_vcpus()

[Lin Ma <lma@suse.com>]

The guest-get-vcpus returns incorrect vcpu info in case we hotunplug vcpus(not
the last one).
e.g.:
A VM has 4 VCPUs: cpu0 + 3 hotunpluggable online vcpus(cpu1, cpu2 and cpu3).
Hotunplug cpu2,  Now only cpu0, cpu1 and cpu3 are present & online.

./qmp-shell /tmp/qmp-monitor.sock
(QEMU) query-hotpluggable-cpus
{"return": [
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 3}, "vcpus-count": 1,
 "qom-path": "/machine/peripheral/cpu3", "type": "host-x86_64-cpu"},
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 2}, "vcpus-count": 1,
 "qom-path": "/machine/peripheral/cpu2", "type": "host-x86_64-cpu"},
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 1}, "vcpus-count": 1,
 "qom-path": "/machine/peripheral/cpu1", "type": "host-x86_64-cpu"},
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 0}, "vcpus-count": 1,
 "qom-path": "/machine/unattached/device[0]", "type": "host-x86_64-cpu"}
]}

(QEMU) device_del id=cpu2
{"return": {}}

(QEMU) query-hotpluggable-cpus
{"return": [
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 3}, "vcpus-count": 1,
 "qom-path": "/machine/peripheral/cpu3", "type": "host-x86_64-cpu"},
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 2}, "vcpus-count": 1,
 "type": "host-x86_64-cpu"},
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 1}, "vcpus-count": 1,
 "qom-path": "/machine/peripheral/cpu1", "type": "host-x86_64-cpu"},
{"props": {"core-id": 0, "thread-id": 0, "socket-id": 0}, "vcpus-count": 1,
 "qom-path": "/machine/unattached/device[0]", "type": "host-x86_64-cpu"}
]}

Before:
./qmp-shell -N /tmp/qmp-ga.sock
Welcome to the QMP low-level shell!
Connected
(QEMU) guest-get-vcpus
{"return": [
{"online": true, "can-offline": false, "logical-id": 0},
{"online": true, "can-offline": true, "logical-id": 1}]}

After:
./qmp-shell -N /tmp/qmp-ga.sock
Welcome to the QMP low-level shell!
Connected
(QEMU) guest-get-vcpus
{"return": [
{"online": true, "can-offline": false, "logical-id": 0},
{"online": true, "can-offline": true, "logical-id": 1},
{"online": true, "can-offline": true, "logical-id": 3}]}

Signed-off-by: Lin Ma <lma@suse.com>
---
 qga/commands-posix.c | 45 ++++++++++++++++----------------------------
 1 file changed, 16 insertions(+), 29 deletions(-)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index c089e38120..ee05e694d3 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -2376,24 +2376,6 @@ error:
     return NULL;
 }
 
-#define SYSCONF_EXACT(name, errp) sysconf_exact((name), #name, (errp))
-
-static long sysconf_exact(int name, const char *name_str, Error **errp)
-{
-    long ret;
-
-    errno = 0;
-    ret = sysconf(name);
-    if (ret == -1) {
-        if (errno == 0) {
-            error_setg(errp, "sysconf(%s): value indefinite", name_str);
-        } else {
-            error_setg_errno(errp, errno, "sysconf(%s)", name_str);
-        }
-    }
-    return ret;
-}
-
 /* Transfer online/offline status between @vcpu and the guest system.
  *
  * On input either @errp or *@errp must be NULL.
@@ -2464,24 +2446,29 @@ static void transfer_vcpu(GuestLogicalProcessor *vcpu, bool sys2vcpu,
 
 GuestLogicalProcessorList *qmp_guest_get_vcpus(Error **errp)
 {
-    int64_t current;
     GuestLogicalProcessorList *head, **link;
-    long sc_max;
+    g_autofree char *cpu_dir = NULL;
+    const gchar *line;
+    GDir *cpu_gdir = NULL;
     Error *local_err = NULL;
 
-    current = 0;
     head = NULL;
     link = &head;
-    sc_max = SYSCONF_EXACT(_SC_NPROCESSORS_CONF, &local_err);
+    cpu_dir = g_strdup_printf("/sys/devices/system/cpu");
+    cpu_gdir = g_dir_open(cpu_dir, 0, NULL);
+
+    if (cpu_gdir == NULL) {
+        error_setg_errno(errp, errno, "failed to list entries: %s", cpu_dir);
+        return NULL;
+    }
 
-    while (local_err == NULL && current < sc_max) {
+    while (local_err == NULL && (line = g_dir_read_name(cpu_gdir)) != NULL) {
         GuestLogicalProcessor *vcpu;
         GuestLogicalProcessorList *entry;
-        int64_t id = current++;
-        char *path = g_strdup_printf("/sys/devices/system/cpu/cpu%" PRId64 "/",
-                                     id);
-
-        if (g_file_test(path, G_FILE_TEST_EXISTS)) {
+        int64_t id;
+        if (sscanf(line, "cpu%ld", &id)) {
+            g_autofree char *path = g_strdup_printf("/sys/devices/system/cpu/"
+                                                    "cpu%" PRId64 "/", id);
             vcpu = g_malloc0(sizeof *vcpu);
             vcpu->logical_id = id;
             vcpu->has_can_offline = true; /* lolspeak ftw */
@@ -2491,8 +2478,8 @@ GuestLogicalProcessorList *qmp_guest_get_vcpus(Error **errp)
             *link = entry;
             link = &entry->next;
         }
-        g_free(path);
     }
+    g_dir_close(cpu_gdir);
 
     if (local_err == NULL) {
         /* there's no guest with zero VCPUs */
-- 
2.26.0