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/libfs.c

@@ -8,6 +8,7 @@
 #include <linux/mount.h>
 #include <linux/vfs.h>
 #include <linux/mutex.h>
+#include <linux/exportfs.h>
 
 #include <asm/uaccess.h>
 
@@ -678,6 +679,93 @@ out:
 	return ret;
 }
 
+/*
+ * This is what d_alloc_anon should have been.  Once the exportfs
+ * argument transition has been finished I will update d_alloc_anon
+ * to this prototype and this wrapper will go away.   --hch
+ */
+static struct dentry *exportfs_d_alloc(struct inode *inode)
+{
+	struct dentry *dentry;
+
+	if (!inode)
+		return NULL;
+	if (IS_ERR(inode))
+		return ERR_PTR(PTR_ERR(inode));
+
+	dentry = d_alloc_anon(inode);
+	if (!dentry) {
+		iput(inode);
+		dentry = ERR_PTR(-ENOMEM);
+	}
+	return dentry;
+}
+
+/**
+ * generic_fh_to_dentry - generic helper for the fh_to_dentry export operation
+ * @sb:		filesystem to do the file handle conversion on
+ * @fid:	file handle to convert
+ * @fh_len:	length of the file handle in bytes
+ * @fh_type:	type of file handle
+ * @get_inode:	filesystem callback to retrieve inode
+ *
+ * This function decodes @fid as long as it has one of the well-known
+ * Linux filehandle types and calls @get_inode on it to retrieve the
+ * inode for the object specified in the file handle.
+ */
+struct dentry *generic_fh_to_dentry(struct super_block *sb, struct fid *fid,
+		int fh_len, int fh_type, struct inode *(*get_inode)
+			(struct super_block *sb, u64 ino, u32 gen))
+{
+	struct inode *inode = NULL;
+
+	if (fh_len < 2)
+		return NULL;
+
+	switch (fh_type) {
+	case FILEID_INO32_GEN:
+	case FILEID_INO32_GEN_PARENT:
+		inode = get_inode(sb, fid->i32.ino, fid->i32.gen);
+		break;
+	}
+
+	return exportfs_d_alloc(inode);
+}
+EXPORT_SYMBOL_GPL(generic_fh_to_dentry);
+
+/**
+ * generic_fh_to_dentry - generic helper for the fh_to_parent export operation
+ * @sb:		filesystem to do the file handle conversion on
+ * @fid:	file handle to convert
+ * @fh_len:	length of the file handle in bytes
+ * @fh_type:	type of file handle
+ * @get_inode:	filesystem callback to retrieve inode
+ *
+ * This function decodes @fid as long as it has one of the well-known
+ * Linux filehandle types and calls @get_inode on it to retrieve the
+ * inode for the _parent_ object specified in the file handle if it
+ * is specified in the file handle, or NULL otherwise.
+ */
+struct dentry *generic_fh_to_parent(struct super_block *sb, struct fid *fid,
+		int fh_len, int fh_type, struct inode *(*get_inode)
+			(struct super_block *sb, u64 ino, u32 gen))
+{
+	struct inode *inode = NULL;
+
+	if (fh_len <= 2)
+		return NULL;
+
+	switch (fh_type) {
+	case FILEID_INO32_GEN_PARENT:
+		inode = get_inode(sb, fid->i32.parent_ino,
+				  (fh_len > 3 ? fid->i32.parent_gen : 0));
+		break;
+	}
+
+	return exportfs_d_alloc(inode);
+}
+EXPORT_SYMBOL_GPL(generic_fh_to_parent);
+
 EXPORT_SYMBOL(dcache_dir_close);
 EXPORT_SYMBOL(dcache_dir_lseek);
 EXPORT_SYMBOL(dcache_dir_open);