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>

3 files changed, 248 insertions, 6 deletions

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 813011aad700..99294a23cd54 100644
--- a/fs/exportfs/expfs.c
+++ b/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 {
+                        return export_decode_fh(mnt->mnt_sb, fid->raw, fh_len,
+                                        fileid_type, acceptable, context);
+                }
+        }
+
+        /*
+         * 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 {
-                result = export_decode_fh(mnt->mnt_sb, fid->raw, fh_len,
-                                          fileid_type, acceptable, context);
+                /*
+                 * 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;
         }
 
-        return result;
+ err_result:
+        dput(result);
+        return ERR_PTR(err);
 }
 EXPORT_SYMBOL_GPL(exportfs_decode_fh);
 
diff --git a/fs/libfs.c b/fs/libfs.c
index ae51481e45e5..6e68b700958d 100644
--- a/fs/libfs.c
+++ b/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);
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 06178a1336ff..b44f6b6871c8 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -4,6 +4,7 @@
 #include <linux/types.h>
 
 struct dentry;
+struct inode;
 struct super_block;
 struct vfsmount;
 
@@ -101,6 +102,21 @@ struct fid {
  *    the filehandle fragment.  encode_fh() should return the number of bytes
  *    stored or a negative error code such as %-ENOSPC
  *
+ * fh_to_dentry:
+ *    @fh_to_dentry is given a &struct super_block (@sb) and a file handle
+ *    fragment (@fh, @fh_len). It should return a &struct dentry which refers
+ *    to the same file that the file handle fragment refers to.  If it cannot,
+ *    it should return a %NULL pointer if the file was found but no acceptable
+ *    &dentries were available, or an %ERR_PTR error code indicating why it
+ *    couldn't be found (e.g. %ENOENT or %ENOMEM).  Any suitable dentry can be
+ *    returned including, if necessary, a new dentry created with d_alloc_root.
+ *    The caller can then find any other extant dentries by following the
+ *    d_alias links.
+ *
+ * fh_to_parent:
+ *    Same as @fh_to_dentry, except that it returns a pointer to the parent
+ *    dentry if it was encoded into the filehandle fragment by @encode_fh.
+ *
  * get_name:
  *    @get_name should find a name for the given @child in the given @parent
  *    directory.  The name should be stored in the @name (with the
@@ -139,6 +155,10 @@ struct export_operations {
                         void *context);
         int (*encode_fh)(struct dentry *de, __u32 *fh, int *max_len,
                         int connectable);
+        struct dentry * (*fh_to_dentry)(struct super_block *sb, struct fid *fid,
+                        int fh_len, int fh_type);
+        struct dentry * (*fh_to_parent)(struct super_block *sb, struct fid *fid,
+                        int fh_len, int fh_type);
         int (*get_name)(struct dentry *parent, char *name,
                         struct dentry *child);
         struct dentry * (*get_parent)(struct dentry *child);
@@ -161,4 +181,14 @@ extern struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
         int fh_len, int fileid_type, int (*acceptable)(void *, struct dentry *),
         void *context);
 
+/*
+ * Generic helpers for filesystems.
+ */
+extern 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));
+extern 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));
+
 #endif /* LINUX_EXPORTFS_H */