balloon: Don't balloon roms
[qemu.git] / util / memfd.c
1 /*
2 * memfd.c
3 *
4 * Copyright (c) 2015 Red Hat, Inc.
5 *
6 * QEMU library functions on POSIX which are shared between QEMU and
7 * the QEMU tools.
8 *
9 * Permission is hereby granted, free of charge, to any person obtaining a copy
10 * of this software and associated documentation files (the "Software"), to deal
11 * in the Software without restriction, including without limitation the rights
12 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
13 * copies of the Software, and to permit persons to whom the Software is
14 * furnished to do so, subject to the following conditions:
15 *
16 * The above copyright notice and this permission notice shall be included in
17 * all copies or substantial portions of the Software.
18 *
19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
20 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
21 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
22 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
23 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
24 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
25 * THE SOFTWARE.
26 */
27
28 #include "qemu/osdep.h"
29
30 #include <glib/gprintf.h>
31
32 #include "qemu/memfd.h"
33
34 #ifdef CONFIG_MEMFD
35 #include <sys/memfd.h>
36 #elif defined CONFIG_LINUX
37 #include <sys/syscall.h>
38 #include <asm/unistd.h>
39
40 static int memfd_create(const char *name, unsigned int flags)
41 {
42 #ifdef __NR_memfd_create
43 return syscall(__NR_memfd_create, name, flags);
44 #else
45 return -1;
46 #endif
47 }
48 #endif
49
50 #ifndef MFD_CLOEXEC
51 #define MFD_CLOEXEC 0x0001U
52 #endif
53
54 #ifndef MFD_ALLOW_SEALING
55 #define MFD_ALLOW_SEALING 0x0002U
56 #endif
57
58 /*
59 * This is a best-effort helper for shared memory allocation, with
60 * optional sealing. The helper will do his best to allocate using
61 * memfd with sealing, but may fallback on other methods without
62 * sealing.
63 */
64 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
65 int *fd)
66 {
67 void *ptr;
68 int mfd = -1;
69
70 *fd = -1;
71
72 #ifdef CONFIG_LINUX
73 if (seals) {
74 mfd = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
75 }
76
77 if (mfd == -1) {
78 /* some systems have memfd without sealing */
79 mfd = memfd_create(name, MFD_CLOEXEC);
80 seals = 0;
81 }
82 #endif
83
84 if (mfd != -1) {
85 if (ftruncate(mfd, size) == -1) {
86 perror("ftruncate");
87 close(mfd);
88 return NULL;
89 }
90
91 if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
92 perror("fcntl");
93 close(mfd);
94 return NULL;
95 }
96 } else {
97 const char *tmpdir = g_get_tmp_dir();
98 gchar *fname;
99
100 fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
101 mfd = mkstemp(fname);
102 unlink(fname);
103 g_free(fname);
104
105 if (mfd == -1) {
106 perror("mkstemp");
107 return NULL;
108 }
109
110 if (ftruncate(mfd, size) == -1) {
111 perror("ftruncate");
112 close(mfd);
113 return NULL;
114 }
115 }
116
117 ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
118 if (ptr == MAP_FAILED) {
119 perror("mmap");
120 close(mfd);
121 return NULL;
122 }
123
124 *fd = mfd;
125 return ptr;
126 }
127
128 void qemu_memfd_free(void *ptr, size_t size, int fd)
129 {
130 if (ptr) {
131 munmap(ptr, size);
132 }
133
134 if (fd != -1) {
135 close(fd);
136 }
137 }
138
139 enum {
140 MEMFD_KO,
141 MEMFD_OK,
142 MEMFD_TODO
143 };
144
145 bool qemu_memfd_check(void)
146 {
147 static int memfd_check = MEMFD_TODO;
148
149 if (memfd_check == MEMFD_TODO) {
150 int fd;
151 void *ptr;
152
153 ptr = qemu_memfd_alloc("test", 4096, 0, &fd);
154 memfd_check = ptr ? MEMFD_OK : MEMFD_KO;
155 qemu_memfd_free(ptr, 4096, fd);
156 }
157
158 return memfd_check == MEMFD_OK;
159 }