File: mtab.c

package info (click to toggle)
aufs-tools 1%3A3.0%2B20120411-2
  • links: PTS
  • area: main
  • in suites: wheezy
  • size: 440 kB
  • sloc: ansic: 3,209; sh: 502; makefile: 136
file content (213 lines) | stat: -rw-r--r-- 4,578 bytes parent folder | download | duplicates (2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
/*
 * Copyright (C) 2005-2011 Junjiro R. Okajima
 *
 * This program, aufs is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

/* cf. fstab.c or the locking for /etc/mtab in util-linux */
/*
 * we need to extract a part of util-linux and create a simple and generic
 * library for locking /etc/mtab.
 */

/* #include <linux/proc_fs.h> */
#define PROC_SUPER_MAGIC 0x9fa0
#include <sys/stat.h>
#include <sys/statfs.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <mntent.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include "au_util.h"

void au_print_ent(struct mntent *ent)
{
	printf("%s on %s type %s (%s)\n",
	       ent->mnt_fsname, ent->mnt_dir, ent->mnt_type, ent->mnt_opts);
}

/* ---------------------------------------------------------------------- */

static void lock_mtab(char *pid_file)
{
	int err, i;

	for (i = 0; i < 5; i++) {
		err = link(pid_file, MTab "~");
		if (!err)
			break;
		sleep(1);
	}
	if (err)
		AuFin(MTab "~");
}

static void unlock_mtab(void)
{
	int err;

	err = rename(MTab "~", MTab);
	if (err)
		AuFin(MTab);
}

static void append_mtab(FILE *fp, FILE *ofp, struct mntent *ent)
{
	int err;
	struct mntent *p;

	while ((p = getmntent(ofp))) {
		err = addmntent(fp, p);
		if (err)
			AuFin("addmntent");
	}

	err = addmntent(fp, ent);
	if (err)
		AuFin("addmntent");
}

/* todo: there are some cases which options are not changed */
static void update_mtab(FILE *fp, char *mntpnt, int do_remount, int do_verbose)
{
	int err;
	long pos;
	FILE *ofp;
	struct mntent ent, *p;

	err = au_proc_getmntent(mntpnt, &ent);
	if (err)
		AuFin("no such mount point");

	ofp = setmntent(MTab, "r");
	if (!ofp)
		AuFin(MTab);

	if (do_remount) {
		/* find the last one */
		pos = -1;
		while ((p = getmntent(ofp))) {
			if (!strcmp(p->mnt_dir, mntpnt))
				pos = ftell(ofp);
		}
		rewind(ofp);

		if (pos > 0) {
			while ((p = getmntent(ofp))) {
				if (ftell(ofp) == pos) {
					/* replace the line */
					p = &ent;
					pos = -1;
				}
				err = addmntent(fp, p);
				if (err)
					AuFin("addmntent");
			}
			if (pos > 0)
				AuFin("internal error");
		} else
			append_mtab(fp, ofp, &ent);
	} else
		append_mtab(fp, ofp, &ent);

	endmntent(ofp); /* ignore */
	if (do_verbose)
		au_print_ent(&ent);
}

/* ---------------------------------------------------------------------- */

int au_update_mtab(char *mntpnt, int do_remount, int do_verbose)
{
	int err, fd, status, e2;
	pid_t pid;
	ino_t ino;
	struct stat st;
	struct statfs stfs;
	struct flock flock = {
		.l_type		= F_WRLCK,
		.l_whence	= SEEK_SET,
		.l_start	= 0,
		.l_len		= 0
	};
	char pid_file[sizeof(MTab "~.") + 20];
	FILE *fp;

	err = statfs(MTab, &stfs);
	if (stfs.f_type == PROC_SUPER_MAGIC)
		return 0;

	snprintf(pid_file, sizeof(pid_file), MTab "~.%d", getpid());
	fd = open(pid_file, O_RDWR | O_CREAT | O_EXCL,
		  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
	if (fd < 0)
		AuFin("%s", pid_file);
	err = fcntl(fd, F_SETLK, &flock);
	if (err)
		AuFin("%s", pid_file);
	fp = fdopen(fd, "r+");
	if (!fp)
		AuFin("%s", pid_file);

	pid = fork();
	if (!pid) {
		lock_mtab(pid_file);
		update_mtab(fp, mntpnt, do_remount, do_verbose);
		unlock_mtab();
		return 0;
	} else if (pid < 0)
		AuFin("fork");

	err = fstat(fd, &st);
	if (err)
		perror(pid_file);
	ino = st.st_ino;

	err = waitpid(pid, &status, 0);
	if (err < 0) {
		perror(pid_file);
		goto out;
	}
	err = !WIFEXITED(status);
	if (!err)
		err = WEXITSTATUS(status);

	e2 = unlink(pid_file);
	if (e2 && errno != ENOENT)
		perror(pid_file);
	e2 = stat(MTab "~", &st);
	if (!e2) {
		if (st.st_ino == ino) {
			/*
			 * The inode number is same,
			 * it means it is we who made the file.
			 * If someone else removed our file between stat(2) and
			 * unlink(2), it is a breakage of the rule.
			 */
			e2 = unlink(MTab "~");
			if (e2)
				perror(MTab);
		}
	} else if (errno != ENOENT)
		perror(MTab "~");
	fclose(fp);

 out:
	return err;
}