9p: Implement TREADLINK operation for 9p2000.L

Synopsis

	size[4] TReadlink tag[2] fid[4]
	size[4] RReadlink tag[2] target[s]

Description
	Readlink is used to return the contents of the symoblic link
        referred by fid. Contents of symboic link is returned as a
        response.

	target[s] - Contents of the symbolic link referred by fid.
Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

fs/9p/vfs_inode.c

@@ -1527,7 +1527,7 @@ static int v9fs_readlink(struct dentry *dentry, char *buffer, int buflen)
 	if (IS_ERR(fid))
 		return PTR_ERR(fid);
 
-	if (!v9fs_proto_dotu(v9ses) && !v9fs_proto_dotl(v9ses))
+	if (!v9fs_proto_dotu(v9ses))
 		return -EBADF;
 
 	st = p9_client_stat(fid);
@@ -1995,6 +1995,60 @@ v9fs_vfs_mknod_dotl(struct inode *dir, struct dentry *dentry, int omode,
 	return err;
 }
 
+static int
+v9fs_vfs_readlink_dotl(struct dentry *dentry, char *buffer, int buflen)
+{
+	int retval;
+	struct p9_fid *fid;
+	char *target = NULL;
+
+	P9_DPRINTK(P9_DEBUG_VFS, " %s\n", dentry->d_name.name);
+	retval = -EPERM;
+	fid = v9fs_fid_lookup(dentry);
+	if (IS_ERR(fid))
+		return PTR_ERR(fid);
+
+	retval = p9_client_readlink(fid, &target);
+	if (retval < 0)
+		return retval;
+
+	strncpy(buffer, target, buflen);
+	P9_DPRINTK(P9_DEBUG_VFS, "%s -> %s\n", dentry->d_name.name, buffer);
+
+	retval = strnlen(buffer, buflen);
+	return retval;
+}
+
+/**
+ * v9fs_vfs_follow_link_dotl - follow a symlink path
+ * @dentry: dentry for symlink
+ * @nd: nameidata
+ *
+ */
+
+static void *
+v9fs_vfs_follow_link_dotl(struct dentry *dentry, struct nameidata *nd)
+{
+	int len = 0;
+	char *link = __getname();
+
+	P9_DPRINTK(P9_DEBUG_VFS, "%s n", dentry->d_name.name);
+
+	if (!link)
+		link = ERR_PTR(-ENOMEM);
+	else {
+		len = v9fs_vfs_readlink_dotl(dentry, link, PATH_MAX);
+		if (len < 0) {
+			__putname(link);
+			link = ERR_PTR(len);
+		} else
+			link[min(len, PATH_MAX-1)] = 0;
+	}
+	nd_set_link(nd, link);
+
+	return NULL;
+}
+
 static const struct inode_operations v9fs_dir_inode_operations_dotu = {
 	.create = v9fs_vfs_create,
 	.lookup = v9fs_vfs_lookup,
@@ -2064,8 +2118,8 @@ static const struct inode_operations v9fs_symlink_inode_operations = {
 };
 
 static const struct inode_operations v9fs_symlink_inode_operations_dotl = {
-	.readlink = generic_readlink,
-	.follow_link = v9fs_vfs_follow_link,
+	.readlink = v9fs_vfs_readlink_dotl,
+	.follow_link = v9fs_vfs_follow_link_dotl,
 	.put_link = v9fs_vfs_put_link,
 	.getattr = v9fs_vfs_getattr_dotl,
 	.setattr = v9fs_vfs_setattr_dotl,

include/net/9p/9p.h

@@ -153,6 +153,8 @@ enum p9_msg_t {
 	P9_RMKNOD,
 	P9_TRENAME = 20,
 	P9_RRENAME,
+	P9_TREADLINK = 22,
+	P9_RREADLINK,
 	P9_TGETATTR = 24,
 	P9_RGETATTR,
 	P9_TSETATTR = 26,

include/net/9p/client.h

@@ -262,5 +262,6 @@ int p9_is_proto_dotu(struct p9_client *clnt);
 int p9_is_proto_dotl(struct p9_client *clnt);
 struct p9_fid *p9_client_xattrwalk(struct p9_fid *, const char *, u64 *);
 int p9_client_xattrcreate(struct p9_fid *, const char *, u64, int);
+int p9_client_readlink(struct p9_fid *fid, char **target);
 
 #endif /* NET_9P_CLIENT_H */

net/9p/client.c

@@ -1870,3 +1870,29 @@ int p9_client_getlock_dotl(struct p9_fid *fid, struct p9_getlock *glock)
 	return err;
 }
 EXPORT_SYMBOL(p9_client_getlock_dotl);
+
+int p9_client_readlink(struct p9_fid *fid, char **target)
+{
+	int err;
+	struct p9_client *clnt;
+	struct p9_req_t *req;
+
+	err = 0;
+	clnt = fid->clnt;
+	P9_DPRINTK(P9_DEBUG_9P, ">>> TREADLINK fid %d\n", fid->fid);
+
+	req = p9_client_rpc(clnt, P9_TREADLINK, "d", fid->fid);
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	err = p9pdu_readf(req->rc, clnt->proto_version, "s", target);
+	if (err) {
+		p9pdu_dump(1, req->rc);
+		goto error;
+	}
+	P9_DPRINTK(P9_DEBUG_9P, "<<< RREADLINK target %s\n", *target);
+error:
+	p9_free_req(clnt, req);
+	return err;
+}
+EXPORT_SYMBOL(p9_client_readlink);