[PATCH] mountd: use separate lockfiles

[Ben Myers <bpm@sgi.com>]

Hi Steve,

I've been having some trouble with locking in mountd under load.  Where
num_threads > 1 rmtab often gets munged.  Here's an attempt to sort that
out.  Tested w/ nfs-utils-1.1.3 and 1.0.7.

Thanks,
	Ben

commit c17d382bcf24d74bfc70088492e5e79f347ee319
Author: Ben Myers <bpm@sgi.com>
Date:   Thu Mar 19 09:46:08 2009 -0500

    Mountd should use separate lockfiles
    
    Mountd keeps file descriptors used for locks separate from those used for io
    and seems to assume that the lock will only be released on close of the file
    descriptor that was used with fcntl.  Actually the lock is released when any
    file descriptor for that file is closed.  When setexportent() is called after
    xflock() he closes and reopens the io file descriptor and defeats the lock.
    
    This patch fixes that by using a separate file for locking, cleaning them up
    when finished.
    
    Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/support/export/rmtab.c b/support/export/rmtab.c
index e11a22a..b49e1aa 100644
--- a/support/export/rmtab.c
+++ b/support/export/rmtab.c
@@ -57,7 +57,7 @@ rmtab_read(void)
 		   file. */
 		int	lockid;
 		FILE	*fp;
-		if ((lockid = xflock(_PATH_RMTAB, "w")) < 0)
+		if ((lockid = xflock(_PATH_RMTABLCK, "w")) < 0)
 			return -1;
 		rewindrmtabent();
 		if (!(fp = fsetrmtabent(_PATH_RMTABTMP, "w"))) {
diff --git a/support/export/xtab.c b/support/export/xtab.c
index 510765a..3b1dcce 100644
--- a/support/export/xtab.c
+++ b/support/export/xtab.c
@@ -23,7 +23,7 @@
 static void cond_rename(char *newfile, char *oldfile);
 
 static int
-xtab_read(char *xtab, int is_export)
+xtab_read(char *xtab, char *lockfn, int is_export)
 {
     /* is_export == 0  => reading /proc/fs/nfs/exports - we know these things are exported to kernel
      * is_export == 1  => reading /var/lib/nfs/etab - these things are allowed to be exported
@@ -33,7 +33,7 @@ xtab_read(char *xtab, int is_export)
 	nfs_export		*exp;
 	int			lockid;
 
-	if ((lockid = xflock(xtab, "r")) < 0)
+	if ((lockid = xflock(lockfn, "r")) < 0)
 		return 0;
 	setexportent(xtab, "r");
 	while ((xp = getexportent(is_export==0, 0)) != NULL) {
@@ -66,18 +66,20 @@ xtab_mount_read(void)
 	int fd;
 	if ((fd=open(_PATH_PROC_EXPORTS, O_RDONLY))>=0) {
 		close(fd);
-		return xtab_read(_PATH_PROC_EXPORTS, 0);
+		return xtab_read(_PATH_PROC_EXPORTS,
+				 _PATH_PROC_EXPORTS, 0);
 	} else if ((fd=open(_PATH_PROC_EXPORTS_ALT, O_RDONLY) >= 0)) {
 		close(fd);
-		return xtab_read(_PATH_PROC_EXPORTS_ALT, 0);
+		return xtab_read(_PATH_PROC_EXPORTS_ALT,
+				 _PATH_PROC_EXPORTS_ALT, 0);
 	} else
-		return xtab_read(_PATH_XTAB, 2);
+		return xtab_read(_PATH_XTAB, _PATH_XTABLCK, 2);
 }
 
 int
 xtab_export_read(void)
 {
-	return xtab_read(_PATH_ETAB, 1);
+	return xtab_read(_PATH_ETAB, _PATH_ETABLCK, 1);
 }
 
 /*
@@ -87,13 +89,13 @@ xtab_export_read(void)
  * fix the auth_reload logic as well...
  */
 static int
-xtab_write(char *xtab, char *xtabtmp, int is_export)
+xtab_write(char *xtab, char *xtabtmp, char *lockfn, int is_export)
 {
 	struct exportent	xe;
 	nfs_export		*exp;
 	int			lockid, i;
 
-	if ((lockid = xflock(xtab, "w")) < 0) {
+	if ((lockid = xflock(lockfn, "w")) < 0) {
 		xlog(L_ERROR, "can't lock %s for writing", xtab);
 		return 0;
 	}
@@ -124,13 +126,13 @@ xtab_write(char *xtab, char *xtabtmp, int is_export)
 int
 xtab_export_write()
 {
-	return xtab_write(_PATH_ETAB, _PATH_ETABTMP, 1);
+	return xtab_write(_PATH_ETAB, _PATH_ETABTMP, _PATH_ETABLCK, 1);
 }
 
 int
 xtab_mount_write()
 {
-	return xtab_write(_PATH_XTAB, _PATH_XTABTMP, 0);
+	return xtab_write(_PATH_XTAB, _PATH_XTABTMP, _PATH_XTABLCK, 0);
 }
 
 void
@@ -139,7 +141,7 @@ xtab_append(nfs_export *exp)
 	struct exportent xe;
 	int		lockid;
 
-	if ((lockid = xflock(_PATH_XTAB, "w")) < 0)
+	if ((lockid = xflock(_PATH_XTABLCK, "w")) < 0)
 		return;
 	setexportent(_PATH_XTAB, "a");
 	xe = exp->m_export;
diff --git a/support/include/nfslib.h b/support/include/nfslib.h
index a51d79d..9d0d39d 100644
--- a/support/include/nfslib.h
+++ b/support/include/nfslib.h
@@ -34,18 +34,27 @@
 #ifndef _PATH_XTABTMP
 #define _PATH_XTABTMP		NFS_STATEDIR "/xtab.tmp"
 #endif
+#ifndef _PATH_XTABLCK
+#define _PATH_XTABLCK		NFS_STATEDIR "/.xtab.lock"
+#endif
 #ifndef _PATH_ETAB
 #define _PATH_ETAB		NFS_STATEDIR "/etab"
 #endif
 #ifndef _PATH_ETABTMP
 #define _PATH_ETABTMP		NFS_STATEDIR "/etab.tmp"
 #endif
+#ifndef _PATH_ETABLCK
+#define _PATH_ETABLCK		NFS_STATEDIR "/.etab.lock"
+#endif
 #ifndef _PATH_RMTAB
 #define _PATH_RMTAB		NFS_STATEDIR "/rmtab"
 #endif
 #ifndef _PATH_RMTABTMP
 #define _PATH_RMTABTMP		_PATH_RMTAB ".tmp"
 #endif
+#ifndef _PATH_RMTABLCK
+#define _PATH_RMTABLCK		NFS_STATEDIR "/.rmtab.lock"
+#endif
 #ifndef _PATH_PROC_EXPORTS
 #define	_PATH_PROC_EXPORTS	"/proc/fs/nfs/exports"
 #define	_PATH_PROC_EXPORTS_ALT	"/proc/fs/nfsd/exports"
diff --git a/support/nfs/xio.c b/support/nfs/xio.c
index f21f5f0..76fb9a1 100644
--- a/support/nfs/xio.c
+++ b/support/nfs/xio.c
@@ -17,6 +17,7 @@
 #include <ctype.h>
 #include <signal.h>
 #include <unistd.h>
+#include <errno.h>
 #include "xmalloc.h"
 #include "xlog.h"
 #include "xio.h"
@@ -58,12 +59,17 @@ xflock(char *fname, char *type)
 	struct flock	fl = { readonly? F_RDLCK : F_WRLCK, SEEK_SET, 0, 0, 0 };
 	int		fd;
 
-	if (readonly)
-		fd = open(fname, O_RDONLY);
-	else
-		fd = open(fname, (O_RDWR|O_CREAT), mode);
+again:
+	fd = open(fname, readonly ? O_RDONLY : (O_RDWR|O_CREAT), 0600);
+	if (fd < 0 && readonly && errno == ENOENT) {
+		/* create a new lockfile */
+		fd = open(fname, O_RDONLY|O_CREAT, 0600);
+		if (fd < 0 && errno == EEXIST) 
+			goto again;	/* raced with another creator */
+	}
 	if (fd < 0) {
-		xlog(L_WARNING, "could not open %s for locking", fname);
+		xlog(L_WARNING, "could not open %s for locking: %s",
+				fname, strerror(errno));
 		return -1;
 	}
 
@@ -74,7 +80,8 @@ xflock(char *fname, char *type)
 	alarm(10);
 	if (fcntl(fd, F_SETLKW, &fl) < 0) {
 		alarm(0);
-		xlog(L_WARNING, "failed to lock %s", fname);
+		xlog(L_WARNING, "failed to lock %s: %s",
+				fname, strerror(errno));
 		close(fd);
 		fd = 0;
 	} else {
diff --git a/utils/mountd/mountd.c b/utils/mountd/mountd.c
index 8084359..25d292b 100644
--- a/utils/mountd/mountd.c
+++ b/utils/mountd/mountd.c
@@ -88,6 +88,14 @@ unregister_services (void)
 		pmap_unset (MOUNTPROG, MOUNTVERS_NFSV3);
 }
 
+static void
+cleanup_lockfiles (void)
+{
+	unlink(_PATH_XTABLCK);
+	unlink(_PATH_ETABLCK);
+	unlink(_PATH_RMTABLCK);
+}
+
 /* Wait for all worker child processes to exit and reap them */
 static void
 wait_for_workers (void)
@@ -154,6 +162,7 @@ fork_workers(void)
 	/* in parent */
 	wait_for_workers();
 	unregister_services();
+	cleanup_lockfiles();
 	xlog(L_NOTICE, "mountd: no more workers, exiting\n");
 	exit(0);
 }
@@ -170,6 +179,7 @@ killer (int sig)
 		kill(0, SIGTERM);
 		wait_for_workers();
 	}
+	cleanup_lockfiles();
 	xlog (L_FATAL, "Caught signal %d, un-registering and exiting.", sig);
 }
 
diff --git a/utils/mountd/rmtab.c b/utils/mountd/rmtab.c
index 5787ed6..c371f8d 100644
--- a/utils/mountd/rmtab.c
+++ b/utils/mountd/rmtab.c
@@ -58,7 +58,7 @@ mountlist_add(char *host, const char *path)
 	int		lockid;
 	long		pos;
 
-	if ((lockid = xflock(_PATH_RMTAB, "a")) < 0)
+	if ((lockid = xflock(_PATH_RMTABLCK, "a")) < 0)
 		return;
 	setrmtabent("r+");
 	while ((rep = getrmtabent(1, &pos)) != NULL) {
@@ -98,7 +98,7 @@ mountlist_del(char *hname, const char *path)
 	int		lockid;
 	int		match;
 
-	if ((lockid = xflock(_PATH_RMTAB, "w")) < 0)
+	if ((lockid = xflock(_PATH_RMTABLCK, "w")) < 0)
 		return;
 	if (!setrmtabent("r")) {
 		xfunlock(lockid);
@@ -139,7 +139,7 @@ mountlist_del_all(struct sockaddr_in *sin)
 	FILE		*fp;
 	int		lockid;
 
-	if ((lockid = xflock(_PATH_RMTAB, "w")) < 0)
+	if ((lockid = xflock(_PATH_RMTABLCK, "w")) < 0)
 		return;
 	if (!(hp = gethostbyaddr((char *)&addr, sizeof(addr), AF_INET))) {
 		xlog(L_ERROR, "can't get hostname of %s", inet_ntoa(addr));
@@ -188,7 +188,7 @@ mountlist_list(void)
 	struct in_addr		addr;
 	struct hostent		*he;
 
-	if ((lockid = xflock(_PATH_RMTAB, "r")) < 0)
+	if ((lockid = xflock(_PATH_RMTABLCK, "r")) < 0)
 		return NULL;
 	if (stat(_PATH_RMTAB, &stb) < 0) {
 		xlog(L_ERROR, "can't stat %s", _PATH_RMTAB);