Add host_memory_backend_pagesize() helper

There are a couple places (one generic, one target specific) where we need
to get the host page size associated with a particular memory backend.  I
have some upcoming code which will add another place which wants this.  So,
for convenience, add a helper function to calculate this.

host_memory_backend_pagesize() returns the host pagesize for a given
HostMemoryBackend object.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>

backends/hostmem.c

@@ -18,6 +18,7 @@
 #include "qapi/visitor.h"
 #include "qemu/config-file.h"
 #include "qom/object_interfaces.h"
+#include "qemu/mmap-alloc.h"
 
 #ifdef CONFIG_NUMA
 #include <numaif.h>
@@ -262,6 +263,23 @@ bool host_memory_backend_is_mapped(HostMemoryBackend *backend)
     return backend->is_mapped;
 }
 
+#ifdef __linux__
+size_t host_memory_backend_pagesize(HostMemoryBackend *memdev)
+{
+    Object *obj = OBJECT(memdev);
+    char *path = object_property_get_str(obj, "mem-path", NULL);
+    size_t pagesize = qemu_mempath_getpagesize(path);
+
+    g_free(path);
+    return pagesize;
+}
+#else
+size_t host_memory_backend_pagesize(HostMemoryBackend *memdev)
+{
+    return getpagesize();
+}
+#endif
+
 static void
 host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
 {

exec.c

@@ -1491,9 +1491,8 @@ static int find_max_supported_pagesize(Object *obj, void *opaque)
     long *hpsize_min = opaque;
 
     if (object_dynamic_cast(obj, TYPE_MEMORY_BACKEND)) {
-        char *mem_path = object_property_get_str(obj, "mem-path", NULL);
-        long hpsize = qemu_mempath_getpagesize(mem_path);
-        g_free(mem_path);
+        long hpsize = host_memory_backend_pagesize(MEMORY_BACKEND(obj));
+
         if (hpsize < *hpsize_min) {
             *hpsize_min = hpsize;
         }

include/sysemu/hostmem.h

@@ -68,4 +68,6 @@ MemoryRegion *host_memory_backend_get_memory(HostMemoryBackend *backend,
 
 void host_memory_backend_set_mapped(HostMemoryBackend *backend, bool mapped);
 bool host_memory_backend_is_mapped(HostMemoryBackend *backend);
+size_t host_memory_backend_pagesize(HostMemoryBackend *memdev);
+
 #endif

target/ppc/kvm.c

@@ -496,11 +496,7 @@ static void kvm_fixup_page_sizes(PowerPCCPU *cpu)
 bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path)
 {
     Object *mem_obj = object_resolve_path(obj_path, NULL);
-    char *mempath = object_property_get_str(mem_obj, "mem-path", NULL);
-    long pagesize;
-
-    pagesize = qemu_mempath_getpagesize(mempath);
-    g_free(mempath);
+    long pagesize = host_memory_backend_pagesize(MEMORY_BACKEND(mem_obj));
 
     return pagesize >= max_cpu_page_size;
 }