exportfs: add new methods

Add the guts for the new filesystem API to exportfs.

There's now a fh_to_dentry method that returns a dentry for the object looked
for given a filehandle fragment, and a fh_to_parent operation that returns the
dentry for the encoded parent directory in case the file handle contains it.

There are default implementations for these methods that only take a callback
for an nfs-enhanced iget variant and implement the rest of the semantics.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Neil Brown <neilb@suse.de>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: <linux-ext4@vger.kernel.org>
Cc: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: Anton Altaparmakov <aia21@cantab.net>
Cc: David Chinner <dgc@sgi.com>
Cc: Timothy Shimmin <tes@sgi.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Chris Mason <mason@suse.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: "Vladimir V. Saveliev" <vs@namesys.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exportfs/expfs.c

@@ -514,17 +514,141 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
 		int (*acceptable)(void *, struct dentry *), void *context)
 {
 	struct export_operations *nop = mnt->mnt_sb->s_export_op;
-	struct dentry *result;
+	struct dentry *result, *alias;
+	int err;
 
-	if (nop->decode_fh) {
-		result = nop->decode_fh(mnt->mnt_sb, fid->raw, fh_len,
+	/*
+	 * Old way of doing things.  Will go away soon.
+	 */
+	if (!nop->fh_to_dentry) {
+		if (nop->decode_fh) {
+			return nop->decode_fh(mnt->mnt_sb, fid->raw, fh_len,
 					fileid_type, acceptable, context);
-	} else {
-		result = export_decode_fh(mnt->mnt_sb, fid->raw, fh_len,
-					  fileid_type, acceptable, context);
+		} else {
+			return export_decode_fh(mnt->mnt_sb, fid->raw, fh_len,
+					fileid_type, acceptable, context);
+		}
 	}
 
-	return result;
+	/*
+	 * Try to get any dentry for the given file handle from the filesystem.
+	 */
+	result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
+	if (!result)
+		result = ERR_PTR(-ESTALE);
+	if (IS_ERR(result))
+		return result;
+
+	if (S_ISDIR(result->d_inode->i_mode)) {
+		/*
+		 * This request is for a directory.
+		 *
+		 * On the positive side there is only one dentry for each
+		 * directory inode.  On the negative side this implies that we
+		 * to ensure our dentry is connected all the way up to the
+		 * filesystem root.
+		 */
+		if (result->d_flags & DCACHE_DISCONNECTED) {
+			err = reconnect_path(mnt->mnt_sb, result);
+			if (err)
+				goto err_result;
+		}
+
+		if (!acceptable(context, result)) {
+			err = -EACCES;
+			goto err_result;
+		}
+
+		return result;
+	} else {
+		/*
+		 * It's not a directory.  Life is a little more complicated.
+		 */
+		struct dentry *target_dir, *nresult;
+		char nbuf[NAME_MAX+1];
+
+		/*
+		 * See if either the dentry we just got from the filesystem
+		 * or any alias for it is acceptable.  This is always true
+		 * if this filesystem is exported without the subtreecheck
+		 * option.  If the filesystem is exported with the subtree
+		 * check option there's a fair chance we need to look at
+		 * the parent directory in the file handle and make sure
+		 * it's connected to the filesystem root.
+		 */
+		alias = find_acceptable_alias(result, acceptable, context);
+		if (alias)
+			return alias;
+
+		/*
+		 * Try to extract a dentry for the parent directory from the
+		 * file handle.  If this fails we'll have to give up.
+		 */
+		err = -ESTALE;
+		if (!nop->fh_to_parent)
+			goto err_result;
+
+		target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
+				fh_len, fileid_type);
+		if (!target_dir)
+			goto err_result;
+		err = PTR_ERR(target_dir);
+		if (IS_ERR(target_dir))
+			goto err_result;
+
+		/*
+		 * And as usual we need to make sure the parent directory is
+		 * connected to the filesystem root.  The VFS really doesn't
+		 * like disconnected directories..
+		 */
+		err = reconnect_path(mnt->mnt_sb, target_dir);
+		if (err) {
+			dput(target_dir);
+			goto err_result;
+		}
+
+		/*
+		 * Now that we've got both a well-connected parent and a
+		 * dentry for the inode we're after, make sure that our
+		 * inode is actually connected to the parent.
+		 */
+		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));
+			mutex_unlock(&target_dir->d_inode->i_mutex);
+			if (!IS_ERR(nresult)) {
+				if (nresult->d_inode) {
+					dput(result);
+					result = nresult;
+				} else
+					dput(nresult);
+			}
+		}
+
+		/*
+		 * At this point we are done with the parent, but it's pinned
+		 * by the child dentry anyway.
+		 */
+		dput(target_dir);
+
+		/*
+		 * And finally make sure the dentry is actually acceptable
+		 * to NFSD.
+		 */
+		alias = find_acceptable_alias(result, acceptable, context);
+		if (!alias) {
+			err = -EACCES;
+			goto err_result;
+		}
+
+		return alias;
+	}
+
+ err_result:
+	dput(result);
+	return ERR_PTR(err);
 }
 EXPORT_SYMBOL_GPL(exportfs_decode_fh);