1 /*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include <cutils/ashmem.h>
18
19 /*
20 * Implementation of the user-space ashmem API for devices, which have our
21 * ashmem-enabled kernel. See ashmem-sim.c for the "fake" tmp-based version,
22 * used by the simulator.
23 */
24 #define LOG_TAG "ashmem"
25
26 #include <errno.h>
27 #include <fcntl.h>
28 #include <linux/ashmem.h>
29 #include <pthread.h>
30 #include <string.h>
31 #include <sys/ioctl.h>
32 #include <sys/stat.h>
33 #include <sys/sysmacros.h>
34 #include <sys/types.h>
35 #include <unistd.h>
36 #include <log/log.h>
37
38 #define ASHMEM_DEVICE "/dev/ashmem"
39
40 /* ashmem identity */
41 static dev_t __ashmem_rdev;
42 /*
43 * If we trigger a signal handler in the middle of locked activity and the
44 * signal handler calls ashmem, we could get into a deadlock state.
45 */
46 static pthread_mutex_t __ashmem_lock = PTHREAD_MUTEX_INITIALIZER;
47
48 /* logistics of getting file descriptor for ashmem */
__ashmem_open_locked()49 static int __ashmem_open_locked()
50 {
51 int ret;
52 struct stat st;
53
54 int fd = TEMP_FAILURE_RETRY(open(ASHMEM_DEVICE, O_RDWR | O_CLOEXEC));
55 if (fd < 0) {
56 return fd;
57 }
58
59 ret = TEMP_FAILURE_RETRY(fstat(fd, &st));
60 if (ret < 0) {
61 int save_errno = errno;
62 close(fd);
63 errno = save_errno;
64 return ret;
65 }
66 if (!S_ISCHR(st.st_mode) || !st.st_rdev) {
67 close(fd);
68 errno = ENOTTY;
69 return -1;
70 }
71
72 __ashmem_rdev = st.st_rdev;
73 return fd;
74 }
75
__ashmem_open()76 static int __ashmem_open()
77 {
78 int fd;
79
80 pthread_mutex_lock(&__ashmem_lock);
81 fd = __ashmem_open_locked();
82 pthread_mutex_unlock(&__ashmem_lock);
83
84 return fd;
85 }
86
87 /* Make sure file descriptor references ashmem, negative number means false */
__ashmem_is_ashmem(int fd,int fatal)88 static int __ashmem_is_ashmem(int fd, int fatal)
89 {
90 dev_t rdev;
91 struct stat st;
92
93 if (TEMP_FAILURE_RETRY(fstat(fd, &st)) < 0) {
94 return -1;
95 }
96
97 rdev = 0; /* Too much complexity to sniff __ashmem_rdev */
98 if (S_ISCHR(st.st_mode) && st.st_rdev) {
99 pthread_mutex_lock(&__ashmem_lock);
100 rdev = __ashmem_rdev;
101 if (rdev) {
102 pthread_mutex_unlock(&__ashmem_lock);
103 } else {
104 int fd = __ashmem_open_locked();
105 if (fd < 0) {
106 pthread_mutex_unlock(&__ashmem_lock);
107 return -1;
108 }
109 rdev = __ashmem_rdev;
110 pthread_mutex_unlock(&__ashmem_lock);
111
112 close(fd);
113 }
114
115 if (st.st_rdev == rdev) {
116 return 0;
117 }
118 }
119
120 if (fatal) {
121 if (rdev) {
122 LOG_ALWAYS_FATAL("illegal fd=%d mode=0%o rdev=%d:%d expected 0%o %d:%d",
123 fd, st.st_mode, major(st.st_rdev), minor(st.st_rdev),
124 S_IFCHR | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IRGRP,
125 major(rdev), minor(rdev));
126 } else {
127 LOG_ALWAYS_FATAL("illegal fd=%d mode=0%o rdev=%d:%d expected 0%o",
128 fd, st.st_mode, major(st.st_rdev), minor(st.st_rdev),
129 S_IFCHR | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IRGRP);
130 }
131 /* NOTREACHED */
132 }
133
134 errno = ENOTTY;
135 return -1;
136 }
137
ashmem_valid(int fd)138 int ashmem_valid(int fd)
139 {
140 return __ashmem_is_ashmem(fd, 0) >= 0;
141 }
142
143 /*
144 * ashmem_create_region - creates a new ashmem region and returns the file
145 * descriptor, or <0 on error
146 *
147 * `name' is an optional label to give the region (visible in /proc/pid/maps)
148 * `size' is the size of the region, in page-aligned bytes
149 */
ashmem_create_region(const char * name,size_t size)150 int ashmem_create_region(const char *name, size_t size)
151 {
152 int ret, save_errno;
153
154 int fd = __ashmem_open();
155 if (fd < 0) {
156 return fd;
157 }
158
159 if (name) {
160 char buf[ASHMEM_NAME_LEN] = {0};
161
162 strlcpy(buf, name, sizeof(buf));
163 ret = TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_SET_NAME, buf));
164 if (ret < 0) {
165 goto error;
166 }
167 }
168
169 ret = TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_SET_SIZE, size));
170 if (ret < 0) {
171 goto error;
172 }
173
174 return fd;
175
176 error:
177 save_errno = errno;
178 close(fd);
179 errno = save_errno;
180 return ret;
181 }
182
ashmem_set_prot_region(int fd,int prot)183 int ashmem_set_prot_region(int fd, int prot)
184 {
185 int ret = __ashmem_is_ashmem(fd, 1);
186 if (ret < 0) {
187 return ret;
188 }
189
190 return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_SET_PROT_MASK, prot));
191 }
192
ashmem_pin_region(int fd,size_t offset,size_t len)193 int ashmem_pin_region(int fd, size_t offset, size_t len)
194 {
195 // TODO: should LP64 reject too-large offset/len?
196 ashmem_pin pin = { static_cast<uint32_t>(offset), static_cast<uint32_t>(len) };
197
198 int ret = __ashmem_is_ashmem(fd, 1);
199 if (ret < 0) {
200 return ret;
201 }
202
203 return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_PIN, &pin));
204 }
205
ashmem_unpin_region(int fd,size_t offset,size_t len)206 int ashmem_unpin_region(int fd, size_t offset, size_t len)
207 {
208 // TODO: should LP64 reject too-large offset/len?
209 ashmem_pin pin = { static_cast<uint32_t>(offset), static_cast<uint32_t>(len) };
210
211 int ret = __ashmem_is_ashmem(fd, 1);
212 if (ret < 0) {
213 return ret;
214 }
215
216 return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_UNPIN, &pin));
217 }
218
ashmem_get_size_region(int fd)219 int ashmem_get_size_region(int fd)
220 {
221 int ret = __ashmem_is_ashmem(fd, 1);
222 if (ret < 0) {
223 return ret;
224 }
225
226 return TEMP_FAILURE_RETRY(ioctl(fd, ASHMEM_GET_SIZE, NULL));
227 }
228