Updated mountpoint to search for circular mount points when using

the -p parameter. This works around mountpoint not recognizing
circular mounts where /a/b/c/d and /a/b are the same location
(ie the same device and same inode).
Closes Savannah bug #37114.

doc/Changelog

@@ -1,6 +1,11 @@
 sysvinit (2.89) UNRELEASED; urgency=low
 
   [ Jesse Smith ]
+    * Updated mountpoint command with -p flag. The -p flag causes
+      mountpoint to search for circular mount points. For example, if
+      /a/b/c/d is a mount point for /a/b then the former is a valid
+      mount point. This only works on Linux since it uses /proc/mounts.
+      Updated manual page to match. This fix closes Savannah bug #37114.
     * Removed two sleep calls when we are doing sync anyway to make sure
       data is being written. Speeds up reboot time by about two seconds.
     * Fixed Clang compiler warning regarding variable data parameters to sprintf().

man/mountpoint.1

@@ -48,6 +48,19 @@ The name of the command is misleading when the -x option is used,
 but the option is useful for comparing if a directory and a device
 match up, and there is no other command that can print the info easily.
 .PP
+The mountpoint command fails when a directory is binded to one of its grandparents.
+For example, if /a/b/c/d is a mount point for /a/b then mountpoint will report
+/a/b/c/d is not a valid mount point. This is because both the original directory and
+its new mount point share the same inode and device number.
+.PP
+The circular mount problem can be worked around on Linux systems by using 
+the -p flag to check the /proc/mounts file for references to the circular mount bind.
+When using the -p flag, make sure to specify the full path (ie /home/user/mp and
+not just mp). Also, mountpoint may still fail if there are spaces in
+the mount point's path, even when using the -p flag because of the way
+/proc/mounts mangles the spaces in the path name. Of course, if the
+admin is using circular mount points with spaces in the name, there
+are bigger concerns.
 .SH AUTHOR
 Miquel van Smoorenburg, miquels@cistron.nl
 .SH "SEE ALSO"

src/mountpoint.c

@@ -50,8 +50,55 @@ int dostat(char *path, struct stat *st, int do_lstat, int quiet)
 	return 0;
 }
 
+
+/*
+This function checks to see if the passed path is listed in the
+/proc/mounts file. If /proc/mounts does not exist or cannot
+be read, we return false. If the path is nout found, we return false.
+If the path is found we return true.
+*/
+int do_proc_check(char *path)
+{
+   FILE *mounts;
+   char *found = NULL, *status;
+   char *target_string;
+   char line[512];
+   int last_character;
+
+   target_string = (char *) calloc( strlen(path) + 3, sizeof(char));
+   if (! target_string)
+      return 0;
+
+   mounts = fopen("/proc/mounts", "r");
+   if (! mounts)
+   {
+      free(target_string);
+      return 0;
+   }
+
+   /* copy path so we can adjust it without harming the original */
+   sprintf(target_string, "%s", path);
+   /* trim trailing slash */
+   last_character = strlen(target_string) - 1;
+   if ( (last_character >= 1) && (target_string[last_character] == '/') )
+        target_string[last_character] = '\0';
+
+   /* Search for path name in /proc/mounts file */
+   status = fgets(line, 512, mounts);
+   while ( (status) && (! found) )
+   {
+       found = strstr(line, target_string);
+       if (! found)
+         status = fgets(line, 512, mounts);
+   }
+   fclose(mounts);
+   free(target_string);
+   return found ? 1 : 0;
+}
+
+
 void usage(void) {
-	fprintf(stderr, "Usage: mountpoint [-q] [-d] [-x] path\n");
+	fprintf(stderr, "Usage: mountpoint [-p] [-q] [-d] [-x] path\n");
 	exit(1);
 }
 
@@ -64,11 +111,15 @@ int main(int argc, char **argv)
 	int		showdev = 0;
 	int		xdev = 0;
 	int		c, r;
+        int             check_proc = 0;
 
-	while ((c = getopt(argc, argv, "dqx")) != EOF) switch(c) {
+	while ((c = getopt(argc, argv, "dpqx")) != EOF) switch(c) {
 		case 'd':
 			showdev = 1;
 			break;
+                case 'p':
+                        check_proc = 1;
+                        break;
 		case 'q':
 			quiet = 1;
 			break;
@@ -118,6 +169,13 @@ int main(int argc, char **argv)
 
 	r = (st.st_dev != st2.st_dev) ||
 	    (st.st_dev == st2.st_dev && st.st_ino == st2.st_ino);
+        /* Mount point was not found yet. If we have access
+           to /proc we can check there too. */
+        if ( (!r) && (check_proc) )
+        {
+           if ( do_proc_check(path) )
+              r = 1;
+        }
 
 	if (!quiet && !showdev)
 		printf("%s is %sa mountpoint\n", path, r ? "" : "not ");