VFS: Allow the filesystem to return a full file pointer on open intent

This is needed by NFSv4 for atomicity reasons: our open command is in
 fact a lookup+open, so we need to be able to propagate open context
 information from lookup() into the resulting struct file's
 private_data field.

 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/namei.c

@@ -28,6 +28,7 @@
 #include <linux/syscalls.h>
 #include <linux/mount.h>
 #include <linux/audit.h>
+#include <linux/file.h>
 #include <asm/namei.h>
 #include <asm/uaccess.h>
 
@@ -317,6 +318,18 @@ void path_release_on_umount(struct nameidata *nd)
 	mntput_no_expire(nd->mnt);
 }
 
+/**
+ * release_open_intent - free up open intent resources
+ * @nd: pointer to nameidata
+ */
+void release_open_intent(struct nameidata *nd)
+{
+	if (nd->intent.open.file->f_dentry == NULL)
+		put_filp(nd->intent.open.file);
+	else
+		fput(nd->intent.open.file);
+}
+
 /*
  * Internal lookup() using the new generic dcache.
  * SMP-safe
@@ -1052,6 +1065,70 @@ out:
 	return retval;
 }
 
+static int __path_lookup_intent_open(const char *name, unsigned int lookup_flags,
+		struct nameidata *nd, int open_flags, int create_mode)
+{
+	struct file *filp = get_empty_filp();
+	int err;
+
+	if (filp == NULL)
+		return -ENFILE;
+	nd->intent.open.file = filp;
+	nd->intent.open.flags = open_flags;
+	nd->intent.open.create_mode = create_mode;
+	err = path_lookup(name, lookup_flags|LOOKUP_OPEN, nd);
+	if (IS_ERR(nd->intent.open.file)) {
+		if (err == 0) {
+			err = PTR_ERR(nd->intent.open.file);
+			path_release(nd);
+		}
+	} else if (err != 0)
+		release_open_intent(nd);
+	return err;
+}
+
+/**
+ * path_lookup_open - lookup a file path with open intent
+ * @name: pointer to file name
+ * @lookup_flags: lookup intent flags
+ * @nd: pointer to nameidata
+ * @open_flags: open intent flags
+ */
+int path_lookup_open(const char *name, unsigned int lookup_flags,
+		struct nameidata *nd, int open_flags)
+{
+	return __path_lookup_intent_open(name, lookup_flags, nd,
+			open_flags, 0);
+}
+
+/**
+ * path_lookup_create - lookup a file path with open + create intent
+ * @name: pointer to file name
+ * @lookup_flags: lookup intent flags
+ * @nd: pointer to nameidata
+ * @open_flags: open intent flags
+ * @create_mode: create intent flags
+ */
+int path_lookup_create(const char *name, unsigned int lookup_flags,
+		struct nameidata *nd, int open_flags, int create_mode)
+{
+	return __path_lookup_intent_open(name, lookup_flags|LOOKUP_CREATE, nd,
+			open_flags, create_mode);
+}
+
+int __user_path_lookup_open(const char __user *name, unsigned int lookup_flags,
+		struct nameidata *nd, int open_flags)
+{
+	char *tmp = getname(name);
+	int err = PTR_ERR(tmp);
+
+	if (!IS_ERR(tmp)) {
+		err = __path_lookup_intent_open(tmp, lookup_flags, nd, open_flags, 0);
+		putname(tmp);
+	}
+	return err;
+}
+
 /*
  * Restricted form of lookup. Doesn't follow links, single-component only,
  * needs parent already locked. Doesn't follow mounts.
@@ -1416,27 +1493,27 @@ int may_open(struct nameidata *nd, int acc_mode, int flag)
  */
 int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
 {
-	int acc_mode, error = 0;
+	int acc_mode, error;
 	struct path path;
 	struct dentry *dir;
 	int count = 0;
 
 	acc_mode = ACC_MODE(flag);
 
+	/* O_TRUNC implies we need access checks for write permissions */
+	if (flag & O_TRUNC)
+		acc_mode |= MAY_WRITE;
+
 	/* Allow the LSM permission hook to distinguish append 
 	   access from general write access. */
 	if (flag & O_APPEND)
 		acc_mode |= MAY_APPEND;
 
-	/* Fill in the open() intent data */
-	nd->intent.open.flags = flag;
-	nd->intent.open.create_mode = mode;
-
 	/*
 	 * The simplest case - just a plain lookup.
 	 */
 	if (!(flag & O_CREAT)) {
-		error = path_lookup(pathname, lookup_flags(flag)|LOOKUP_OPEN, nd);
+		error = path_lookup_open(pathname, lookup_flags(flag), nd, flag);
 		if (error)
 			return error;
 		goto ok;
@@ -1445,7 +1522,7 @@ int open_namei(const char * pathname, int flag, int mode, struct nameidata *nd)
 	/*
 	 * Create - we need to know the parent.
 	 */
-	error = path_lookup(pathname, LOOKUP_PARENT|LOOKUP_OPEN|LOOKUP_CREATE, nd);
+	error = path_lookup_create(pathname, LOOKUP_PARENT, nd, flag, mode);
 	if (error)
 		return error;
 
@@ -1520,6 +1597,8 @@ ok:
 exit_dput:
 	dput_path(&path, nd);
 exit:
+	if (!IS_ERR(nd->intent.open.file))
+		release_open_intent(nd);
 	path_release(nd);
 	return error;