remount_service.c revision c880ee0265a4057fd5086f4b9e8e5fae6e053087 
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 <stdlib.h>
18#include <stdio.h>
19#include <unistd.h>
20#include <string.h>
21#include <fcntl.h>
22#include <sys/mount.h>
23#include <errno.h>
24
25#include "sysdeps.h"
26
27#define  TRACE_TAG  TRACE_ADB
28#include "adb.h"
29
30
31static int system_ro = 1;
32
33/* Returns the device used to mount a directory in /proc/mounts */
34static char *find_mount(const char *dir)
35{
36    int fd;
37    int res;
38    int size;
39    char *token = NULL;
40    const char delims[] = "\n";
41    char buf[4096];
42
43    fd = unix_open("/proc/mounts", O_RDONLY);
44    if (fd < 0)
45        return NULL;
46
47    buf[sizeof(buf) - 1] = '\0';
48    size = adb_read(fd, buf, sizeof(buf) - 1);
49    adb_close(fd);
50
51    token = strtok(buf, delims);
52
53    while (token) {
54        char mount_dev[256];
55        char mount_dir[256];
56        int mount_freq;
57        int mount_passno;
58
59        res = sscanf(token, "%255s %255s %*s %*s %d %d\n",
60                     mount_dev, mount_dir, &mount_freq, &mount_passno);
61        mount_dev[255] = 0;
62        mount_dir[255] = 0;
63        if (res == 4 && (strcmp(dir, mount_dir) == 0))
64            return strdup(mount_dev);
65
66        token = strtok(NULL, delims);
67    }
68    return NULL;
69}
70
71/* Init mounts /system as read only, remount to enable writes. */
72static int remount_system()
73{
74    char *dev;
75
76    if (system_ro == 0) {
77        return 0;
78    }
79
80    dev = find_mount("/system");
81
82    if (!dev)
83        return -1;
84
85    system_ro = mount(dev, "/system", "none", MS_REMOUNT, NULL);
86
87    free(dev);
88
89    return system_ro;
90}
91
92static void write_string(int fd, const char* str)
93{
94    writex(fd, str, strlen(str));
95}
96
97void remount_service(int fd, void *cookie)
98{
99    int ret = remount_system();
100
101    if (!ret)
102       write_string(fd, "remount succeeded\n");
103    else {
104        char    buffer[200];
105        snprintf(buffer, sizeof(buffer), "remount failed: %s\n", strerror(errno));
106        write_string(fd, buffer);
107    }
108
109    adb_close(fd);
110}
111
112