[unix-history] / usr / src / usr.sbin / amd / config / mtab_file.c

/*
 * $Id: mtab_file.c,v 5.2 90/06/23 22:20:54 jsp Rel $
 *
 * Copyright (c) 1990 Jan-Simon Pendry
 * Copyright (c) 1990 Imperial College of Science, Technology & Medicine
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry at Imperial College, London.
 *
 * %sccs.include.redist.c%
 *
 *	@(#)mtab_file.c	5.1 (Berkeley) %G%
 */

#include "am.h"

#ifdef READ_MTAB_FROM_FILE

#ifdef USE_FCNTL
#include <fcntl.h>
#else
#include <sys/file.h>
#endif /* USE_FCNTL */

#ifdef UPDATE_MTAB

/*
 * Do strict /etc/mtab locking
 */
#define	MTAB_LOCKING

/*
 * Firewall mtab entries
 */
#define	MTAB_STRIPNL

#include <sys/stat.h>
static FILE *mnt_file;

/*
 * If the system is being trashed by something, then
 * opening mtab may fail with ENFILE.  So, go to sleep
 * for a second and try again. (Yes - this has happened to me.)
 *
 * Note that this *may* block the automounter, oh well. 
 * If we get to this state then things are badly wrong anyway...
 *
 * Give the system 10 seconds to recover but then give up.
 * Hopefully something else will exit and free up some file
 * table slots in that time.
 */
#define	NFILE_RETRIES	10 /* seconds */

#ifdef MTAB_LOCKING
#ifdef LOCK_FCNTL
static int lock(fd)
{
	int rc;
	struct flock lk;

	lk.l_type = F_WRLCK;
	lk.l_whence = 0;
	lk.l_start = 0;
	lk.l_len = 0;

again:
	rc = fcntl(fd, F_SETLKW, (caddr_t) &lk);
	if (rc < 0 && (errno == EACCES || errno == EAGAIN)) {
#ifdef DEBUG
		dlog("Blocked, trying to obtain exclusive mtab lock");
#endif /* DEBUG */
		sleep(1);
		goto again;
	}
	return rc;
}
#else
#define lock(fd) (flock((fd), LOCK_EX))
#endif /* LOCK_FCNTL */
#endif /* MTAB_LOCKING */

/*
 * Unlock the mount table
 */
void unlock_mntlist()
{
	/*
	 * Release file lock, by closing the file
	 */
	if (mnt_file) {
		endmntent(mnt_file);
		mnt_file = 0;
	}
}

/*
 * Write out a mount list
 */
void rewrite_mtab(mp)
mntlist *mp;
{
	FILE *mfp;

	/*
	 * Concoct a temporary name in the same
	 * directory as the target mount table
	 * so that rename() will work.
	 */
	char tmpname[64];
	int retries;
	int tmpfd;
	char *cp;
	char *mcp = mtab;
	cp = strrchr(mcp, '/');
	if (cp) {
		bcopy(mcp, tmpname, cp - mcp);
		tmpname[cp-mcp] = '\0';
	} else {
		plog(XLOG_WARNING, "No '/' in mtab (%s), using \".\" as tmp directory", mtab);
		tmpname[0] = '.'; tmpname[1] = '\0';
	}
	strcat(tmpname, "/mtabXXXXXX");
	mktemp(tmpname);
	retries = 0;
enfile1:
	if ((tmpfd = open(tmpname, O_RDWR|O_CREAT|O_TRUNC, 0644)) < 0) {
		if (errno == ENFILE && retries++ < NFILE_RETRIES) {
			sleep(1);
			goto enfile1;
		}
		plog(XLOG_ERROR, "%s: open: %m", tmpname);
		return;
	}
	if (close(tmpfd) < 0)
		plog(XLOG_ERROR, "Couldn't close tmp file descriptor: %m");

	retries = 0;
enfile2:
	mfp = setmntent(tmpname, "w");
	if (!mfp) {
		if (errno == ENFILE && retries++ < NFILE_RETRIES) {
			sleep(1);
			goto enfile2;
		}
		plog(XLOG_ERROR, "setmntent(\"%s\", \"w\"): %m", tmpname);
		return;
	}

	while (mp) {
		if (mp->mnt)
			if (addmntent(mfp, mp->mnt))
				plog(XLOG_ERROR, "Can't write entry to %s", tmpname);
		mp = mp->mnext;
	}

	endmntent(mfp);

	/*
	 * Rename temporary mtab to real mtab
	 */
	if (rename(tmpname, mtab) < 0)
		plog(XLOG_ERROR, "rename %s to %s: %m", tmpname, mtab);
}

#ifdef MTAB_STRIPNL
static void mtab_stripnl(s)
char *s;
{
	do {
		s = strchr(s, '\n');
		if (s)
			*s++ = ' ';
	} while (s);
}
#endif /* MTAB_STRIPNL */

/*
 * Append a mntent structure to the
 * current mount table.
 */
void write_mntent(mp)
struct mntent *mp;
{
	int retries = 0;
	FILE *mfp;
enfile:
	mfp = setmntent(mtab, "a");
	if (mfp) {
#ifdef MTAB_STRIPNL
		mtab_stripnl(mp->mnt_opts);
#endif /* MTAB_STRIPNL */
		if (addmntent(mfp, mp))
			plog(XLOG_ERROR, "Couldn't write %s: %m", mtab);
		endmntent(mfp);
	} else {
		if (errno == ENFILE && retries < NFILE_RETRIES) {
			sleep(1);
			goto enfile;
		}
		plog(XLOG_ERROR, "setmntent(\"%s\", \"a\"): %m", mtab);
	}
}

#endif /* UPDATE_MTAB */

static struct mntent *mnt_dup(mp)
struct mntent *mp;
{
	struct mntent *new_mp = ALLOC(mntent);

	new_mp->mnt_fsname = strdup(mp->mnt_fsname);
	new_mp->mnt_dir = strdup(mp->mnt_dir);
	new_mp->mnt_type = strdup(mp->mnt_type);
	new_mp->mnt_opts = strdup(mp->mnt_opts);

	new_mp->mnt_freq = mp->mnt_freq;
	new_mp->mnt_passno = mp->mnt_passno;

	return new_mp;
}

/*
 * Read a mount table into memory
 */
mntlist *read_mtab(fs)
char *fs;
{
	mntlist **mpp, *mhp;

	struct mntent *mep;
	FILE *mfp = 0;

#ifdef UPDATE_MTAB
	/*
	 * There is a possible race condition if two processes enter
	 * this routine at the same time.  One will be blocked by the
	 * exclusive lock below (or by the shared lock in setmntent)
	 * and by the time the second process has the exclusive lock
	 * it will be on the wrong underlying object.  To check for this
	 * the mtab file is stat'ed before and after all the locking
	 * sequence, and if it is a different file then we assume that
	 * it may be the wrong file (only "may", since there is another
	 * race between the initial stat and the setmntent).
	 *
	 * Simpler solutions to this problem are invited...
	 */
	int racing = 0;
#ifdef MTAB_LOCKING
	int rc;
	int retries = 0;
	struct stat st_before, st_after;
#endif /* MTAB_LOCKING */

	if (mnt_file) {
#ifdef DEBUG
		dlog("Forced close on %s in read_mtab", mtab);
#endif /* DEBUG */
		endmntent(mnt_file);
		mnt_file = 0;
	}

#ifdef MTAB_LOCKING
again:
	if (mfp) {
		endmntent(mfp);
		mfp = 0;
	}

	clock_valid = 0;
	if (stat(mtab, &st_before) < 0) {
		plog(XLOG_ERROR, "%s: stat: %m", mtab);
		if (errno == ESTALE) {
			/* happens occasionally */
			sleep(1);
			goto again;
		}
		return 0;
	}
#endif /* MTAB_LOCKING */
#endif /* UPDATE_MTAB */

eacces:
	mfp = setmntent(mtab, "r+");
	if (!mfp) {
		/*
		 * Since setmntent locks the descriptor, it
		 * is possible it can fail... so retry if
		 * needed.
		 */
		if (errno == EACCES || errno == EAGAIN) {
#ifdef DEBUG
			dlog("Blocked, trying to obtain exclusive mtab lock");
#endif /* DEBUG */
			goto eacces;
		} else if (errno == ENFILE && retries++ < NFILE_RETRIES) {
			sleep(1);
			goto eacces;
		}

		plog(XLOG_ERROR, "setmntent(\"%s\", \"r+\"): %m", mtab);
		return 0;
	}

#ifdef MTAB_LOCKING
#ifdef UPDATE_MTAB
	/*
	 * At this point we have an exclusive lock on the mount list,
	 * but it may be the wrong one so...
	 */

	/*
	 * Need to get an exclusive lock on the current
	 * mount table until we have a new copy written
	 * out, when the lock is released in free_mntlist.
	 * flock is good enough since the mount table is
	 * not shared between machines.
	 */
	do
		rc = lock(fileno(mfp));
	while (rc < 0 && errno == EINTR);
	if (rc < 0) {
		plog(XLOG_ERROR, "Couldn't lock %s: %m", mtab);
		endmntent(mfp);
		return 0;
	}
	/*
	 * Now check whether the mtab file has changed under our feet
	 */
	if (stat(mtab, &st_after) < 0) {
		plog(XLOG_ERROR, "%s: stat", mtab);
		goto again;
	}

	if (st_before.st_dev != st_after.st_dev ||
		st_before.st_ino != st_after.st_ino) {
			if (racing == 0) {
				/* Sometimes print a warning */
				plog(XLOG_WARNING,
					"Possible mount table race - retrying %s", fs);
			}
			racing = (racing+1) & 3;
			goto again;
	}
#endif /* UPDATE_MTAB */
#endif /* MTAB_LOCKING */

	mpp = &mhp;

/*
 * XXX - In SunOS 4 there is (yet another) memory leak
 * which loses 1K the first time getmntent is called.
 * (jsp)
 */
	while (mep = getmntent(mfp)) {
		/*
		 * Allocate a new slot
		 */
		*mpp = ALLOC(mntlist);

		/*
		 * Copy the data returned by getmntent
		 */
		(*mpp)->mnt = mnt_dup(mep);

		/*
		 * Move to next pointer
		 */
		mpp = &(*mpp)->mnext;
	}
	*mpp = 0;

#ifdef UPDATE_MTAB
	/*
	 * If we are not updating the mount table then we
	 * can free the resources held here, otherwise they
	 * must be held until the mount table update is complete
	 */
	mnt_file = mfp;
#else
	endmntent(mfp);
#endif /* UPDATE_MTAB */

	return mhp;
}

#endif /* READ_MTAB_FROM_FILE */
Commit	Line	Data
e1a31032 KM	1	/*
	2	* $Id: mtab_file.c,v 5.2 90/06/23 22:20:54 jsp Rel $
	3	*
	4	* Copyright (c) 1990 Jan-Simon Pendry
	5	* Copyright (c) 1990 Imperial College of Science, Technology & Medicine
	6	* Copyright (c) 1990 The Regents of the University of California.
	7	* All rights reserved.
	8	*
	9	* This code is derived from software contributed to Berkeley by
	10	* Jan-Simon Pendry at Imperial College, London.
	11	*
	12	* %sccs.include.redist.c%
	13	*
	14	* @(#)mtab_file.c 5.1 (Berkeley) %G%
	15	*/
	16
	17	#include "am.h"
	18
	19	#ifdef READ_MTAB_FROM_FILE
	20
	21	#ifdef USE_FCNTL
	22	#include <fcntl.h>
	23	#else
	24	#include <sys/file.h>
	25	#endif /* USE_FCNTL */
	26
	27	#ifdef UPDATE_MTAB
	28
	29	/*
	30	* Do strict /etc/mtab locking
	31	*/
	32	#define MTAB_LOCKING
	33
	34	/*
	35	* Firewall mtab entries
	36	*/
	37	#define MTAB_STRIPNL
	38
	39	#include <sys/stat.h>
	40	static FILE *mnt_file;
	41
	42	/*
	43	* If the system is being trashed by something, then
	44	* opening mtab may fail with ENFILE. So, go to sleep
	45	* for a second and try again. (Yes - this has happened to me.)
	46	*
	47	* Note that this may block the automounter, oh well.
	48	* If we get to this state then things are badly wrong anyway...
	49	*
	50	* Give the system 10 seconds to recover but then give up.
	51	* Hopefully something else will exit and free up some file
	52	* table slots in that time.
	53	*/
	54	#define NFILE_RETRIES 10 /* seconds */
	55
	56	#ifdef MTAB_LOCKING
	57	#ifdef LOCK_FCNTL
	58	static int lock(fd)
	59	{
	60	int rc;
	61	struct flock lk;
	62
	63	lk.l_type = F_WRLCK;
	64	lk.l_whence = 0;
65	lk.l_start = 0;
66	lk.l_len = 0;
67
68	again:
69	rc = fcntl(fd, F_SETLKW, (caddr_t) &lk);
70	if (rc < 0 && (errno == EACCES \|\| errno == EAGAIN)) {
71	#ifdef DEBUG
72	dlog("Blocked, trying to obtain exclusive mtab lock");
73	#endif /* DEBUG */
74	sleep(1);
75	goto again;
76	}
77	return rc;
78	}
79	#else
80	#define lock(fd) (flock((fd), LOCK_EX))
81	#endif /* LOCK_FCNTL */
82	#endif /* MTAB_LOCKING */
83
84	/*
85	* Unlock the mount table
86	*/
87	void unlock_mntlist()
88	{
89	/*
90	* Release file lock, by closing the file
91	*/
92	if (mnt_file) {
93	endmntent(mnt_file);
94	mnt_file = 0;
95	}
96	}
97
98	/*
99	* Write out a mount list
100	*/
101	void rewrite_mtab(mp)
102	mntlist *mp;
103	{
104	FILE *mfp;
105
106	/*
107	* Concoct a temporary name in the same
108	* directory as the target mount table
109	* so that rename() will work.
110	*/
111	char tmpname[64];
112	int retries;
113	int tmpfd;
114	char *cp;
115	char *mcp = mtab;
116	cp = strrchr(mcp, '/');
117	if (cp) {
118	bcopy(mcp, tmpname, cp - mcp);
119	tmpname[cp-mcp] = '\0';
120	} else {
121	plog(XLOG_WARNING, "No '/' in mtab (%s), using \".\" as tmp directory", mtab);
122	tmpname[0] = '.'; tmpname[1] = '\0';
123	}
124	strcat(tmpname, "/mtabXXXXXX");
125	mktemp(tmpname);
126	retries = 0;
127	enfile1:
128	if ((tmpfd = open(tmpname, O_RDWR\|O_CREAT\|O_TRUNC, 0644)) < 0) {
129	if (errno == ENFILE && retries++ < NFILE_RETRIES) {
130	sleep(1);
131	goto enfile1;
132	}
133	plog(XLOG_ERROR, "%s: open: %m", tmpname);
134	return;
135	}
136	if (close(tmpfd) < 0)
137	plog(XLOG_ERROR, "Couldn't close tmp file descriptor: %m");
138
139	retries = 0;
140	enfile2:
141	mfp = setmntent(tmpname, "w");
142	if (!mfp) {
143	if (errno == ENFILE && retries++ < NFILE_RETRIES) {
144	sleep(1);
145	goto enfile2;
146	}
147	plog(XLOG_ERROR, "setmntent(\"%s\", \"w\"): %m", tmpname);
148	return;
149	}
150
151	while (mp) {
152	if (mp->mnt)
153	if (addmntent(mfp, mp->mnt))
154	plog(XLOG_ERROR, "Can't write entry to %s", tmpname);
155	mp = mp->mnext;
156	}
157
158	endmntent(mfp);
159
160	/*
161	* Rename temporary mtab to real mtab
162	*/
163	if (rename(tmpname, mtab) < 0)
164	plog(XLOG_ERROR, "rename %s to %s: %m", tmpname, mtab);
165	}
166
167	#ifdef MTAB_STRIPNL
168	static void mtab_stripnl(s)
169	char *s;
170	{
171	do {
172	s = strchr(s, '\n');
173	if (s)
174	*s++ = ' ';
175	} while (s);
176	}
177	#endif /* MTAB_STRIPNL */
178
179	/*
180	* Append a mntent structure to the
181	* current mount table.
182	*/
183	void write_mntent(mp)
184	struct mntent *mp;
185	{
186	int retries = 0;
187	FILE *mfp;
188	enfile:
189	mfp = setmntent(mtab, "a");
190	if (mfp) {
191	#ifdef MTAB_STRIPNL
192	mtab_stripnl(mp->mnt_opts);
193	#endif /* MTAB_STRIPNL */
194	if (addmntent(mfp, mp))
195	plog(XLOG_ERROR, "Couldn't write %s: %m", mtab);
196	endmntent(mfp);
197	} else {
198	if (errno == ENFILE && retries < NFILE_RETRIES) {
199	sleep(1);
200	goto enfile;
201	}
202	plog(XLOG_ERROR, "setmntent(\"%s\", \"a\"): %m", mtab);
203	}
204	}
205
206	#endif /* UPDATE_MTAB */
207
208	static struct mntent *mnt_dup(mp)
209	struct mntent *mp;
210	{
211	struct mntent *new_mp = ALLOC(mntent);
212
213	new_mp->mnt_fsname = strdup(mp->mnt_fsname);
214	new_mp->mnt_dir = strdup(mp->mnt_dir);
215	new_mp->mnt_type = strdup(mp->mnt_type);
216	new_mp->mnt_opts = strdup(mp->mnt_opts);
217
218	new_mp->mnt_freq = mp->mnt_freq;
219	new_mp->mnt_passno = mp->mnt_passno;
220
221	return new_mp;
222	}
223
224	/*
225	* Read a mount table into memory
226	*/
227	mntlist *read_mtab(fs)
228	char *fs;
229	{
230	mntlist *mpp, mhp;
231
232	struct mntent *mep;
233	FILE *mfp = 0;
234
235	#ifdef UPDATE_MTAB
236	/*
237	* There is a possible race condition if two processes enter
238	* this routine at the same time. One will be blocked by the
239	* exclusive lock below (or by the shared lock in setmntent)
240	* and by the time the second process has the exclusive lock
241	* it will be on the wrong underlying object. To check for this
242	* the mtab file is stat'ed before and after all the locking
243	* sequence, and if it is a different file then we assume that
244	* it may be the wrong file (only "may", since there is another
245	* race between the initial stat and the setmntent).
246	*
247	* Simpler solutions to this problem are invited...
248	*/
249	int racing = 0;
250	#ifdef MTAB_LOCKING
251	int rc;
252	int retries = 0;
253	struct stat st_before, st_after;
254	#endif /* MTAB_LOCKING */
255
256	if (mnt_file) {
257	#ifdef DEBUG
258	dlog("Forced close on %s in read_mtab", mtab);
259	#endif /* DEBUG */
260	endmntent(mnt_file);
261	mnt_file = 0;
262	}
263
264	#ifdef MTAB_LOCKING
265	again:
266	if (mfp) {
267	endmntent(mfp);
268	mfp = 0;
269	}
270
271	clock_valid = 0;
272	if (stat(mtab, &st_before) < 0) {
273	plog(XLOG_ERROR, "%s: stat: %m", mtab);
274	if (errno == ESTALE) {
275	/* happens occasionally */
276	sleep(1);
277	goto again;
278	}
279	return 0;
280	}
281	#endif /* MTAB_LOCKING */
282	#endif /* UPDATE_MTAB */
283
284	eacces:
285	mfp = setmntent(mtab, "r+");
286	if (!mfp) {
287	/*
288	* Since setmntent locks the descriptor, it
289	* is possible it can fail... so retry if
290	* needed.
291	*/
292	if (errno == EACCES \|\| errno == EAGAIN) {
293	#ifdef DEBUG
294	dlog("Blocked, trying to obtain exclusive mtab lock");
295	#endif /* DEBUG */
296	goto eacces;
297	} else if (errno == ENFILE && retries++ < NFILE_RETRIES) {
298	sleep(1);
299	goto eacces;
300	}
301
302	plog(XLOG_ERROR, "setmntent(\"%s\", \"r+\"): %m", mtab);
303	return 0;
304	}
305
306	#ifdef MTAB_LOCKING
307	#ifdef UPDATE_MTAB
308	/*
309	* At this point we have an exclusive lock on the mount list,
310	* but it may be the wrong one so...
311	*/
312
313	/*
314	* Need to get an exclusive lock on the current
315	* mount table until we have a new copy written
316	* out, when the lock is released in free_mntlist.
317	* flock is good enough since the mount table is
318	* not shared between machines.
319	*/
320	do
321	rc = lock(fileno(mfp));
322	while (rc < 0 && errno == EINTR);
323	if (rc < 0) {
324	plog(XLOG_ERROR, "Couldn't lock %s: %m", mtab);
325	endmntent(mfp);
326	return 0;
327	}
328	/*
329	* Now check whether the mtab file has changed under our feet
330	*/
331	if (stat(mtab, &st_after) < 0) {
332	plog(XLOG_ERROR, "%s: stat", mtab);
333	goto again;
334	}
335
336	if (st_before.st_dev != st_after.st_dev \|\|
337	st_before.st_ino != st_after.st_ino) {
338	if (racing == 0) {
339	/* Sometimes print a warning */
340	plog(XLOG_WARNING,
341	"Possible mount table race - retrying %s", fs);
342	}
343	racing = (racing+1) & 3;
344	goto again;
345	}
346	#endif /* UPDATE_MTAB */
347	#endif /* MTAB_LOCKING */
348
349	mpp = &mhp;
350
351	/*
352	* XXX - In SunOS 4 there is (yet another) memory leak
353	* which loses 1K the first time getmntent is called.
354	* (jsp)
355	*/
356	while (mep = getmntent(mfp)) {
357	/*
358	* Allocate a new slot
359	*/
360	*mpp = ALLOC(mntlist);
361
362	/*
363	* Copy the data returned by getmntent
364	*/
365	(*mpp)->mnt = mnt_dup(mep);
366
367	/*
368	* Move to next pointer
369	*/
370	mpp = &(*mpp)->mnext;
371	}
372	*mpp = 0;
373
374	#ifdef UPDATE_MTAB
375	/*
376	* If we are not updating the mount table then we
377	* can free the resources held here, otherwise they
378	* must be held until the mount table update is complete
379	*/
380	mnt_file = mfp;
381	#else
382	endmntent(mfp);
383	#endif /* UPDATE_MTAB */
384
385	return mhp;
386	}
387
388	#endif /* READ_MTAB_FROM_FILE */