[Qemu-devel] [QEMU-PPC] [PATCH] powerpc/spapr: Add host threads parameter to ibm, get_system_parameter

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

The ibm,get_system_parameter rtas call is used by the guest to retrieve
data relating to certain parameters of the system. The SPLPAR
characteristics option (token 20) is used to determin characteristics of
the environment in which the lpar will run.

It may be useful for a guest to know the number of physical host threads
present on the underlying system where it is being run. Add the
characteristic "HostThrs" to the SPLPAR Characteristics
ibm,get_system_parameter rtas call to expose this information to a
guest and provide an implementation which determines this information
based on the number of interrupt servers present in the device tree.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
---
 hw/ppc/spapr_rtas.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 5bc1a93271..a33d87794c 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -229,6 +229,40 @@ static inline int sysparm_st(target_ulong addr, target_ulong len,
     return RTAS_OUT_SUCCESS;
 }
 
+static int rtas_get_num_host_threads(void)
+{
+    const char *entry, *name = "/proc/device-tree/cpus/";
+    int num_threads = -1;
+    GDir *dir;
+
+    if (!kvm_enabled())
+        return 1;
+
+    dir = g_dir_open(name, 0, NULL);
+    if (!dir)
+        return -1;
+
+    while ((entry = g_dir_read_name(dir))) {
+        if (!strncmp(entry, "PowerPC,POWER", strlen("PowerPC,POWER"))) {
+            unsigned long len;
+            char *path, *buf;
+
+            path = g_strconcat(name, entry, "/ibm,ppc-interrupt-server#s",
+                               NULL);
+            if (g_file_get_contents(path, &buf, &len, NULL)) {
+                num_threads = len / sizeof(int);
+                g_free(buf);
+            }
+
+            g_free(path);
+            break;
+        }
+    }
+
+    g_dir_close(dir);
+    return num_threads;
+}
+
 static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           SpaprMachineState *spapr,
                                           uint32_t token, uint32_t nargs,
@@ -250,6 +284,16 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
                                           current_machine->ram_size / MiB,
                                           smp_cpus,
                                           max_cpus);
+        int num_host_threads = rtas_get_num_host_threads();
+
+        if (num_host_threads > 0) {
+            char *hostthr_val, *old = param_val;
+
+            hostthr_val = g_strdup_printf(",HostThrs=%d", num_host_threads);
+            param_val = g_strconcat(param_val, hostthr_val, NULL);
+            g_free(hostthr_val);
+            g_free(old);
+        }
         ret = sysparm_st(buffer, length, param_val, strlen(param_val) + 1);
         g_free(param_val);
         break;
-- 
2.13.6