knfsd: exportfs: split out reconnecting a dentry from find_exported_dentry

There's a clear subfunctionality of reconnecting a given dentry to the main
dentry tree in find_exported_dentry, that can be called both for the dentry
we're looking for or it's parent directory.

This patch splits the subfunctionality out into a separate helper to make the
code more readable and document it's intent.  As a nice side-optimization we
can avoid getting a superfluous dentry reference count in the case we need to
reconnect a directory on it's own.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 113 insertions, 100 deletions

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 166d8ca9eaea..8adb32a9387a 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -91,101 +91,27 @@ find_disconnected_root(struct dentry *dentry)
         return dentry;
 }
 
-/**
- * find_exported_dentry - helper routine to implement export_operations->decode_fh
- * @sb:         The &super_block identifying the filesystem
- * @obj:        An opaque identifier of the object to be found - passed to
- *              get_inode
- * @parent:     An optional opqaue identifier of the parent of the object.
- * @acceptable: A function used to test possible &dentries to see if they are
- *              acceptable
- * @context:    A parameter to @acceptable so that it knows on what basis to
- *              judge.
- *
- * find_exported_dentry is the central helper routine to enable file systems
- * to provide the decode_fh() export_operation.  It's main task is to take
- * an &inode, find or create an appropriate &dentry structure, and possibly
- * splice this into the dcache in the correct place.
- *
- * The decode_fh() operation provided by the filesystem should call
- * find_exported_dentry() with the same parameters that it received except
- * that instead of the file handle fragment, pointers to opaque identifiers
- * for the object and optionally its parent are passed.  The default decode_fh
- * routine passes one pointer to the start of the filehandle fragment, and
- * one 8 bytes into the fragment.  It is expected that most filesystems will
- * take this approach, though the offset to the parent identifier may well be
- * different.
+
+/*
+ * Make sure target_dir is fully connected to the dentry tree.
  *
- * find_exported_dentry() will call get_dentry to get an dentry pointer from
- * the file system.  If any &dentry in the d_alias list is acceptable, it will
- * be returned.  Otherwise find_exported_dentry() will attempt to splice a new
- * &dentry into the dcache using get_name() and get_parent() to find the
- * appropriate place.
+ * It may already be, as the flag isn't always updated when connection happens.
  */
-
-struct dentry *
-find_exported_dentry(struct super_block *sb, void *obj, void *parent,
-                     int (*acceptable)(void *context, struct dentry *de),
-                     void *context)
+static int
+reconnect_path(struct super_block *sb, struct dentry *target_dir)
 {
-        struct dentry *result = NULL;
-        struct dentry *target_dir;
-        int err = -ESTALE;
-        struct export_operations *nops = sb->s_export_op;
-        struct dentry *alias;
-        int noprogress;
         char nbuf[NAME_MAX+1];
+        int noprogress = 0;
+        int err = -ESTALE;
 
         /*
-         * Attempt to find the inode.
-         */
-        result = exportfs_get_dentry(sb, obj);
-        if (IS_ERR(result))
-                return result;
-
-        if (S_ISDIR(result->d_inode->i_mode)) {
-                if (!(result->d_flags & DCACHE_DISCONNECTED)) {
-                        if (acceptable(context, result))
-                                return result;
-                        err = -EACCES;
-                        goto err_result;
-                }
-
-                target_dir = dget(result);
-        } else {
-                alias = find_acceptable_alias(result, acceptable, context);
-                if (alias)
-                        return alias;
-
-                if (parent == NULL)
-                        goto err_result;
-
-                target_dir = exportfs_get_dentry(sb,parent);
-                if (IS_ERR(target_dir)) {
-                        err = PTR_ERR(target_dir);
-                        goto err_result;
-                }
-        }
-
-        /*
-         * Now we need to make sure that target_dir is properly connected.
-         * It may already be, as the flag isn't always updated when connection
-         * happens.
-         * So, we walk up parent links until we find a connected directory,
-         * or we run out of directories.  Then we find the parent, find
-         * the name of the child in that parent, and do a lookup.
-         * This should connect the child into the parent
-         * We then repeat.
-         */
-
-        /* it is possible that a confused file system might not let us complete 
+         * It is possible that a confused file system might not let us complete
          * the path to the root.  For example, if get_parent returns a directory
          * in which we cannot find a name for the child.  While this implies a
          * very sick filesystem we don't want it to cause knfsd to spin.  Hence
          * the noprogress counter.  If we go through the loop 10 times (2 is
          * probably enough) without getting anywhere, we just give up
          */
-        noprogress = 0;
         while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
                 struct dentry *pd = find_disconnected_root(target_dir);
 
@@ -221,18 +147,20 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
                         struct dentry *npd;
 
                         mutex_lock(&pd->d_inode->i_mutex);
-                        if (nops->get_parent)
-                                ppd = nops->get_parent(pd);
+                        if (sb->s_export_op->get_parent)
+                                ppd = sb->s_export_op->get_parent(pd);
                         mutex_unlock(&pd->d_inode->i_mutex);
 
                         if (IS_ERR(ppd)) {
                                 err = PTR_ERR(ppd);
-                                dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
-                                        pd->d_inode->i_ino, err);
+                                dprintk("%s: get_parent of %ld failed, err %d\n",
+                                        __FUNCTION__, pd->d_inode->i_ino, err);
                                 dput(pd);
                                 break;
                         }
-                        dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
+
+                        dprintk("%s: find name of %lu in %lu\n", __FUNCTION__,
+                                pd->d_inode->i_ino, ppd->d_inode->i_ino);
                         err = exportfs_get_name(ppd, nbuf, pd);
                         if (err) {
                                 dput(ppd);
@@ -244,13 +172,14 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
                                         continue;
                                 break;
                         }
-                        dprintk("find_exported_dentry: found name: %s\n", nbuf);
+                        dprintk("%s: found name: %s\n", __FUNCTION__, nbuf);
                         mutex_lock(&ppd->d_inode->i_mutex);
                         npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
                         mutex_unlock(&ppd->d_inode->i_mutex);
                         if (IS_ERR(npd)) {
                                 err = PTR_ERR(npd);
-                                dprintk("find_exported_dentry: lookup failed: %d\n", err);
+                                dprintk("%s: lookup failed: %d\n",
+                                        __FUNCTION__, err);
                                 dput(ppd);
                                 dput(pd);
                                 break;
@@ -263,7 +192,7 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
                         if (npd == pd)
                                 noprogress = 0;
                         else
-                                printk("find_exported_dentry: npd != pd\n");
+                                printk("%s: npd != pd\n", __FUNCTION__);
                         dput(npd);
                         dput(ppd);
                         if (IS_ROOT(pd)) {
@@ -279,15 +208,101 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
                 /* something went wrong - oh-well */
                 if (!err)
                         err = -ESTALE;
-                goto err_target;
+                return err;
         }
-        /* if we weren't after a directory, have one more step to go */
-        if (result != target_dir) {
-                struct dentry *nresult;
+
+        return 0;
+}
+
+/**
+ * find_exported_dentry - helper routine to implement export_operations->decode_fh
+ * @sb:         The &super_block identifying the filesystem
+ * @obj:        An opaque identifier of the object to be found - passed to
+ *              get_inode
+ * @parent:     An optional opqaue identifier of the parent of the object.
+ * @acceptable: A function used to test possible &dentries to see if they are
+ *              acceptable
+ * @context:    A parameter to @acceptable so that it knows on what basis to
+ *              judge.
+ *
+ * find_exported_dentry is the central helper routine to enable file systems
+ * to provide the decode_fh() export_operation.  It's main task is to take
+ * an &inode, find or create an appropriate &dentry structure, and possibly
+ * splice this into the dcache in the correct place.
+ *
+ * The decode_fh() operation provided by the filesystem should call
+ * find_exported_dentry() with the same parameters that it received except
+ * that instead of the file handle fragment, pointers to opaque identifiers
+ * for the object and optionally its parent are passed.  The default decode_fh
+ * routine passes one pointer to the start of the filehandle fragment, and
+ * one 8 bytes into the fragment.  It is expected that most filesystems will
+ * take this approach, though the offset to the parent identifier may well be
+ * different.
+ *
+ * find_exported_dentry() will call get_dentry to get an dentry pointer from
+ * the file system.  If any &dentry in the d_alias list is acceptable, it will
+ * be returned.  Otherwise find_exported_dentry() will attempt to splice a new
+ * &dentry into the dcache using get_name() and get_parent() to find the
+ * appropriate place.
+ */
+
+struct dentry *
+find_exported_dentry(struct super_block *sb, void *obj, void *parent,
+                     int (*acceptable)(void *context, struct dentry *de),
+                     void *context)
+{
+        struct dentry *result, *alias;
+        int err = -ESTALE;
+
+        /*
+         * Attempt to find the inode.
+         */
+        result = exportfs_get_dentry(sb, obj);
+        if (IS_ERR(result))
+                return result;
+
+        if (S_ISDIR(result->d_inode->i_mode)) {
+                if (!(result->d_flags & DCACHE_DISCONNECTED)) {
+                        if (acceptable(context, result))
+                                return result;
+                        err = -EACCES;
+                        goto err_result;
+                }
+
+                err = reconnect_path(sb, result);
+                if (err)
+                        goto err_result;
+        } else {
+                struct dentry *target_dir, *nresult;
+                char nbuf[NAME_MAX+1];
+
+                alias = find_acceptable_alias(result, acceptable, context);
+                if (alias)
+                        return alias;
+
+                if (parent == NULL)
+                        goto err_result;
+
+                target_dir = exportfs_get_dentry(sb,parent);
+                if (IS_ERR(target_dir)) {
+                        err = PTR_ERR(target_dir);
+                        goto err_result;
+                }
+
+                err = reconnect_path(sb, target_dir);
+                if (err) {
+                        dput(target_dir);
+                        goto err_result;
+                }
+
+                /*
+                 * As we weren't after a directory, have one more step to go.
+                 */
                 err = exportfs_get_name(target_dir, nbuf, result);
                 if (!err) {
                         mutex_lock(&target_dir->d_inode->i_mutex);
-                        nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
+                        nresult = lookup_one_len(nbuf, target_dir,
+                                                 strlen(nbuf));
                         mutex_unlock(&target_dir->d_inode->i_mutex);
                         if (!IS_ERR(nresult)) {
                                 if (nresult->d_inode) {
@@ -297,8 +312,8 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
                                         dput(nresult);
                         }
                 }
+                dput(target_dir);
         }
-        dput(target_dir);
 
         alias = find_acceptable_alias(result, acceptable, context);
         if (alias)
@@ -308,13 +323,11 @@ find_exported_dentry(struct super_block *sb, void *obj, void *parent,
         dput(result);
         /* It might be justifiable to return ESTALE here,
          * but the filehandle at-least looks reasonable good
-         * and it just be a permission problem, so returning
+         * and it may just be a permission problem, so returning
          * -EACCESS is safer
          */
         return ERR_PTR(-EACCES);
 
- err_target:
-        dput(target_dir);
  err_result:
         dput(result);
         return ERR_PTR(err);