1 files changed, 100 insertions, 18 deletions

diff --git a/modules/mount_bind.c b/modules/mount_bind.c
index 5eb45b7..5a4580e 100644
--- a/modules/mount_bind.c
+++ b/modules/mount_bind.c
@@ -21,6 +21,8 @@
 #include <unistd.h>
 #include <syslog.h>
 #include <string.h>
+#include <limits.h>
+#include <time.h>
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -31,8 +33,82 @@
 #define MODPREFIX "mount(bind): "
 int mount_version = AUTOFS_MOUNT_VERSION; /* Required by protocol */
 
+static int have_mount_bind = -1; /* -1 means: not tested yet */
+
+/* This gives a conservative estimate for the number of hex digits it
+   may require to printf() type T. */
+#define HEXDIGITS(T) ((sizeof(T)*CHAR_BIT+3)/4)
+
+/* Test to see if "mount --bind" works properly or not */
+static int mount_bind_works_p(void)
+{
+  char testdir[32+HEXDIGITS(time_t)+HEXDIGITS(pid_t)];
+  char dir1[40+HEXDIGITS(time_t)+HEXDIGITS(pid_t)];
+  char dir2[40+HEXDIGITS(time_t)+HEXDIGITS(pid_t)];
+  struct stat st1, st2;
+  pid_t mypid = getpid();
+  int rv;
+  int bind_works = 0;		/* Guilty until proven innocent */
+  
+  syslog(LOG_DEBUG, MODPREFIX "Testing if \"mount --bind\" works correctly...");
+
+  /* Make a safe temporary directory */
+  do {
+    sprintf(testdir, "/tmp/autofs-bind-%lx-%lx",
+	    (unsigned long)time(NULL), (unsigned long)mypid);
+    rv = mkdir(testdir, 0700);
+    if ( rv && errno != EEXIST ) {
+      syslog(LOG_ERR, MODPREFIX "Cannot create temporary directory: %m");
+      goto f0;
+    }
+  } while ( rv );
+
+  sprintf(dir1, "%s/dir1", testdir);
+  sprintf(dir2, "%s/dir2", testdir);
+
+  if ( mkdir(dir1, 0700) )
+    goto f1;
+  if ( mkdir(dir2, 0700) )
+    goto f2;
+
+  syslog(LOG_DEBUG, MODPREFIX "calling mount --bind %s %s",
+	 dir1, dir2);
+  if ( spawnl(LOG_DEBUG, PATH_MOUNT, PATH_MOUNT, "--bind",
+	      dir1, dir2, NULL) ) {
+    syslog(LOG_DEBUG, MODPREFIX "mount --bind failed");
+    goto f3;
+  }
+
+  /* mount --bind returned OK, now verify it did the right thing */
+  if ( stat(dir1, &st1) || stat(dir2, &st2) ) {
+    syslog(LOG_DEBUG, MODPREFIX "Cannot stat temporary directories: %m");
+    goto f4;
+  }
+  
+  /* If dir1 and dir2 are now the same directory, mount --bind worked */
+  if ( st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino )
+    bind_works = 1;
+
+  /* Disassemble the test setup */
+ f4:
+  /* umount the bind */
+  spawnl(LOG_DEBUG, PATH_UMOUNT, PATH_UMOUNT, dir2, NULL);
+ f3:
+  rmdir(dir2);
+ f2:
+  rmdir(dir1);
+ f1:
+  rmdir(testdir);
+ f0:
+  return bind_works;
+}
+
 int mount_init(void **context)
 {
+  if ( have_mount_bind == -1 ) {
+    /* Need to figure out if mount --bind works or not */
+    have_mount_bind = mount_bind_works_p();
+  }
   return 0;
 }
 
@@ -41,7 +117,7 @@ int mount_mount(const char *root, const char *name, int name_len,
 		void *context)
 {
   char *fullpath;
-  int err;
+  int err = 0;
 
   fullpath = alloca(strlen(root)+name_len+2);
   if ( !fullpath ) {
@@ -49,27 +125,33 @@ int mount_mount(const char *root, const char *name, int name_len,
     return 1;
   }
   sprintf(fullpath, "%s/%s", root, name);
+
+  if ( have_mount_bind ) {
+    syslog(LOG_DEBUG, MODPREFIX "calling mkdir %s", fullpath);
+    if ( mkdir(fullpath, 0555) && errno != EEXIST ) {
+      syslog(LOG_NOTICE, MODPREFIX "mkdir %s failed: %m", name);
+      return 1;
+    }
     
-  syslog(LOG_DEBUG, MODPREFIX "calling mkdir %s", fullpath);
-  if ( mkdir(fullpath, 0555) && errno != EEXIST ) {
-    syslog(LOG_NOTICE, MODPREFIX "mkdir %s failed: %m", name);
-    return 1;
+    syslog(LOG_DEBUG, MODPREFIX "calling mount --bind %s %s",
+	   what, fullpath);
+    err = spawnl(LOG_NOTICE, PATH_MOUNT, PATH_MOUNT, "--bind",
+		 what, fullpath, NULL);
+
+    if ( err ) {
+      if ( rmdir(fullpath) && errno == EBUSY ) {
+	return 0;
+      } else {
+	/* This shouldn't happen, but try anyway... */
+	syslog(LOG_NOTICE, MODPREFIX "failed to mount --bind %s on %s, trying symlink",
+	       what, fullpath);
+      }
+    }
   }
-    
-  syslog(LOG_DEBUG, MODPREFIX "calling mount --bind %s %s",
-	 fstype, what, fullpath);
-  err = spawnl(LOG_NOTICE, PATH_MOUNT, PATH_MOUNT, "--bind",
-	       what, fullpath, NULL);
-  
-  if ( err ) {
-    if ( rmdir(fullpath) && errno == EBUSY )
-      return 0;
 
-    syslog(LOG_DEBUG, MODPREFIX "failed to mount --bind %s on %s, trying symlink",
-	   what, fullpath);
+  if ( err || !have_mount_bind ) {
     if ( symlink(what, fullpath) && errno != EEXIST ) {
-      syslog(LOG_NOTICE, MODPREFIX "failed to create local mount %s -> %s", fullpath, what);
-      
+      syslog(LOG_NOTICE, MODPREFIX "failed to create symlink %s -> %s", fullpath, what);
       return 1;
     } else {
       syslog(LOG_DEBUG, MODPREFIX "symlinked %s -> %s", fullpath, what);