1 /*
2 * QEMU host POSIX shared memory object backend
3 *
4 * Copyright (C) 2024 Red Hat Inc
5 *
6 * Authors:
7 * Stefano Garzarella <sgarzare@redhat.com>
8 *
9 * This work is licensed under the terms of the GNU GPL, version 2 or later.
10 * See the COPYING file in the top-level directory.
11 */
12
13 #include "qemu/osdep.h"
14 #include "system/hostmem.h"
15 #include "qapi/error.h"
16 #include "migration/cpr.h"
17
18 #define TYPE_MEMORY_BACKEND_SHM "memory-backend-shm"
19
20 OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendShm, MEMORY_BACKEND_SHM)
21
22 struct HostMemoryBackendShm {
23 HostMemoryBackend parent_obj;
24 };
25
26 static bool
shm_backend_memory_alloc(HostMemoryBackend * backend,Error ** errp)27 shm_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
28 {
29 g_autofree char *backend_name = host_memory_backend_get_name(backend);
30 uint32_t ram_flags;
31 int fd = cpr_find_fd(backend_name, 0);
32
33 if (!backend->size) {
34 error_setg(errp, "can't create shm backend with size 0");
35 return false;
36 }
37
38 if (!backend->share) {
39 error_setg(errp, "can't create shm backend with `share=off`");
40 return false;
41 }
42
43 if (fd >= 0) {
44 goto have_fd;
45 }
46
47 fd = qemu_shm_alloc(backend->size, errp);
48 if (fd < 0) {
49 return false;
50 }
51 cpr_save_fd(backend_name, 0, fd);
52
53 have_fd:
54 /* Let's do the same as memory-backend-ram,share=on would do. */
55 ram_flags = RAM_SHARED;
56 ram_flags |= backend->reserve ? 0 : RAM_NORESERVE;
57 ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0;
58
59 return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend),
60 backend_name, backend->size,
61 ram_flags, fd, 0, errp);
62 }
63
64 static void
shm_backend_instance_init(Object * obj)65 shm_backend_instance_init(Object *obj)
66 {
67 HostMemoryBackendShm *m = MEMORY_BACKEND_SHM(obj);
68
69 MEMORY_BACKEND(m)->share = true;
70 }
71
72 static void
shm_backend_class_init(ObjectClass * oc,const void * data)73 shm_backend_class_init(ObjectClass *oc, const void *data)
74 {
75 HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
76
77 bc->alloc = shm_backend_memory_alloc;
78 }
79
80 static const TypeInfo shm_backend_info = {
81 .name = TYPE_MEMORY_BACKEND_SHM,
82 .parent = TYPE_MEMORY_BACKEND,
83 .instance_init = shm_backend_instance_init,
84 .class_init = shm_backend_class_init,
85 .instance_size = sizeof(HostMemoryBackendShm),
86 };
87
register_types(void)88 static void register_types(void)
89 {
90 type_register_static(&shm_backend_info);
91 }
92
93 type_init(register_types);
94