Changeset 44358c1 in mainline

Timestamp:

2007-11-07T18:46:43Z (17 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

7f3e3e7

Parents:

b818cff

Message:

VFS work.
Increment reference counters for the VFS nodes representing the mount point and
the root of the mounted filesystem, respectively, during VFS_MOUNT. Take the
unlink_futex when transforming the triplet into a VFS node.

Location:

uspace/srv/vfs

Files:

• vfs_mount.c (modified) (7 diffs)
• vfs_unlink.c (modified) (1 diff)

uspace/srv/vfs/vfs_mount.c

@@ -66 +66 @@
 {
         int dev_handle;
+        vfs_node_t *mp_node = NULL;
 
         /*
@@ -137 +138 @@
         /*
          * Lookup the root node of the filesystem being mounted.
+         * In this case, we don't need to take the unlink_futex as the root node
+         * cannot be removed. However, we do take a reference to it so that
+         * we can track how many times it has been mounted.
          */
         int rc;
@@ -146 +150 @@
                 return;
         }
+        vfs_node_t *mr_node = vfs_node_get(&mounted_root);
+        if (!mr_node) {
+                free(buf);
+                ipc_answer_fast_0(rid, ENOMEM);
+                return;
+        }
 
         /*
@@ -156 +166 @@
                  * We already have the root FS.
                  */
+                futex_down(&unlink_futex);
                 rc = vfs_lookup_internal((char *) (buf + FS_NAME_MAXLEN),
                     size - FS_NAME_MAXLEN, &mp, NULL);
@@ -162 +173 @@
                          * The lookup failed for some reason.
                          */
-                        futex_up(&rootfs_futex);
+                        futex_up(&unlink_futex);
+                        futex_up(&rootfs_futex);
+                        vfs_node_put(mr_node);  /* failed -> drop reference */
                         free(buf);
                         ipc_answer_fast_0(rid, rc);
                         return;
                 }
+                mp_node = vfs_node_get(&mp);
+                if (!mp_node) {
+                        futex_up(&unlink_futex);
+                        futex_up(&rootfs_futex);
+                        vfs_node_put(mr_node);  /* failed -> drop reference */
+                        free(buf);
+                        ipc_answer_fast_0(rid, ENOMEM);
+                        return;
+                }
+                /*
+                 * Now we hold a reference to mp_node.
+                 * It will be dropped upon the corresponding VFS_UNMOUNT.
+                 * This prevents the mount point from being deleted.
+                 */
+                futex_up(&unlink_futex);
         } else {
                 /*
@@ -188 +216 @@
                         futex_up(&rootfs_futex);
                         free(buf);
+                        vfs_node_put(mr_node);  /* failed -> drop reference */
                         ipc_answer_fast_0(rid, ENOENT);
                         return;
@@ -218 +247 @@
         vfs_release_phone(phone);
 
+        if ((rc1 != EOK) || (rc2 != EOK)) {
+                /* Mount failed, drop references to mr_node and mp_node. */
+                vfs_node_put(mr_node);
+                if (mp_node)
+                        vfs_node_put(mp_node);
+        }
+        
         if (rc2 == EOK)
                 ipc_answer_fast_0(rid, rc1);

uspace/srv/vfs/vfs_unlink.c

@@ -40 +40 @@
 
 /**
- * This futex serializes concurrent VFS_CREATE, VFS_OPEN and VFS_UNLINK
- * operations.
+ * This futex prevents the race between a triplet-to-VFS-node resolution and a
+ * concurrent VFS_UNLINK or VFS_RMDIR operation.
  */
 atomic_t unlink_futex = FUTEX_INITIALIZER;