Re: [PATCH] nfs-utils: make auth_reload respect sub-second timestamps on etab

[Jeff Layton <jlayton@redhat.com>]

On Thu, May 03, 2007 at 10:55:37AM +1000, Neil Brown wrote:
> On Thursday April 26, jlayton@redhat.com wrote:
> > 
> > This patch seems to fix the problem as well. mountd holds the etab open, but
> > doesn't actually do any I/O on that fd. This makes sure that the inode number
> > of the new etab file won't be the same as the current version that mountd is
> > aware of. I also added a comment to xtab_write to warn people who might
> > consider changing how the files are written.
> > 
> > We might also consider adding back in some of the mtime logic to try and
> > catch programs that edit the file in place, but I'm not sure if that's
> > worthwhile.
> 
> I agree.
> 
> > 
> > Neil, what do you think?
> 
> I was about to say "fine", but then saw the problem.
> Because of the way get_exportlist uses the return value, that value
> needs to unique over all time (or close to it).  So returning the
> inode number won't work (as we have seen that ext3 cycles between
> two).
> 
> A simple event counter could be returned though, which would give
> something unique to get_exportlist.
> 
> NeilBrown

Ahh, good catch. I wasn't considering that mountd might call into auth_reload
from other functions between get_exportlist calls. I'm not sure we even really
need a static counter here though. How about just having auth_reload return
true if the reload occurred?

Signed-off-by: Jeff Layton <jlayton@redhat.com>


diff --git a/support/export/xtab.c b/support/export/xtab.c
index 0ddb251..292087b 100644
--- a/support/export/xtab.c
+++ b/support/export/xtab.c
@@ -80,6 +80,12 @@ xtab_export_read(void)
 	return xtab_read(_PATH_ETAB, 1);
 }
 
+/*
+ * mountd now keeps an open fd for the etab at all times to make sure that the
+ * inode number changes when the xtab_export_write is done. If you change the
+ * routine below such that the files are edited in place, then you'll need to
+ * fix the auth_reload logic as well...
+ */
 static int
 xtab_write(char *xtab, char *xtabtmp, int is_export)
 {
diff --git a/utils/mountd/auth.c b/utils/mountd/auth.c
index 183c9ea..5638a05 100644
--- a/utils/mountd/auth.c
+++ b/utils/mountd/auth.c
@@ -14,6 +14,7 @@
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <errno.h>
+#include <unistd.h>
 #include "misc.h"
 #include "nfslib.h"
 #include "exportfs.h"
@@ -46,24 +47,33 @@ auth_init(char *exports)
 	xtab_mount_write();
 }
 
-time_t
+/* Check the etab file. Reload it and return true if it changed */
+int
 auth_reload()
 {
 	struct stat		stb;
-	static time_t		last_modified = 0;
+	static ino_t		last_inode;
+	static int		last_fd;
+	int			fd;
 
-	if (stat(_PATH_ETAB, &stb) < 0)
+	if ((fd = open(_PATH_ETAB, O_RDONLY)) < 0) {
+		xlog(L_FATAL, "couldn't open %s", _PATH_ETAB);
+	} else if (fstat(fd, &stb) < 0) {
 		xlog(L_FATAL, "couldn't stat %s", _PATH_ETAB);
-	if (stb.st_mtime == last_modified)
-		return last_modified;
-	last_modified = stb.st_mtime;
+	} else if (stb.st_ino == last_inode) {
+		close(fd);
+		return 0;
+	} else {
+		close(last_fd);
+		last_fd = fd;
+		last_inode = stb.st_ino;
+	}
 
 	export_freeall();
 	memset(&my_client, 0, sizeof(my_client));
-	// export_read(export_file);
 	xtab_export_read();
 
-	return last_modified;
+	return 1;
 }
 
 static nfs_export *
diff --git a/utils/mountd/mountd.c b/utils/mountd/mountd.c
index 04141d1..c3324cf 100644
--- a/utils/mountd/mountd.c
+++ b/utils/mountd/mountd.c
@@ -465,19 +465,14 @@ static exports
 get_exportlist(void)
 {
 	static exports		elist = NULL;
-	static time_t		etime = 0;
-	time_t			atime;
 	struct exportnode	*e, *ne;
 	struct groupnode	*g, *ng, *c, **cp;
 	nfs_export		*exp;
 	int			i;
 
-	atime = auth_reload();
-	if (elist && atime == etime)
+	if (auth_reload() == 0)
 		return elist;
 
-	etime = atime;
-
 	for (e = elist; e != NULL; e = ne) {
 		ne = e->ex_next;
 		for (g = e->ex_groups; g != NULL; g = ng) {
diff --git a/utils/mountd/mountd.h b/utils/mountd/mountd.h
index b539278..d64c171 100644
--- a/utils/mountd/mountd.h
+++ b/utils/mountd/mountd.h
@@ -40,7 +40,7 @@ bool_t		mount_mnt_3_svc(struct svc_req *, dirpath *, mountres3 *);
 
 void		mount_dispatch(struct svc_req *, SVCXPRT *);
 void		auth_init(char *export_file);
-time_t		auth_reload(void);
+int		auth_reload(void);
 nfs_export *	auth_authenticate(char *what, struct sockaddr_in *sin,
 					char *path);
 void		auth_export(nfs_export *exp);

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