[PATCH 04/18] VFS: add vfs_lookup_open()

From: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>

vfs_lookup_open() is a limited version of lookup_open() which is
exported for nfsd to use - to replace dentry_create().

It is limited in that no filename is given (thus no auditing) and no
LOOKUP_ flags are passed.  A few "intent" LOOKUP flags are deduced from
the open flags.

Signed-off-by: NeilBrown <neil-+NVA1uvv1dVBDLzU/[email protected]>
---
 fs/namei.c            | 54 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/namei.h |  3 +++
 2 files changed, 57 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 18a43c24d7f1..db3fddbccd21 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4571,6 +4571,60 @@ static struct dentry *lookup_open(const struct path *path, struct file *file,
 	goto out;
 }
 
+/**
+ * vfs_lookup_open - open and possibly create a regular file
+ * @parent: directory to contain file
+ * @last: final component of file name
+ * @open_flag: O_flags
+ * @mode: initial permissions for file
+ *
+ * Open a file after lookup and/or create.  This provides similar
+ * functionality open_last_lookups() for in-kernel users, particularly
+ * nfsd.
+ * It uses ->atomic_open or ->lookup / ->create / ->open as appropriate.
+ *
+ * Returns: the opened struct file, or an error.
+ */
+struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
+			     int open_flag, umode_t mode)
+{
+	struct file *file __free(fput) = NULL;
+	unsigned int lookup_flags = LOOKUP_OPEN;
+	struct dentry *dentry;
+	int error = 0;
+
+	error = lookup_noperm_common(last, parent->dentry);
+	if (error)
+		return ERR_PTR(error);
+
+	file = alloc_empty_file(open_flag, current_cred());
+	if (IS_ERR(file))
+		return file;
+
+	if (open_flag & O_CREAT) {
+		lookup_flags |= LOOKUP_CREATE;
+		if (open_flag & O_EXCL)
+			lookup_flags |= LOOKUP_EXCL;
+	}
+	dentry = lookup_open(parent, file, last, lookup_flags, NULL,
+			     open_flag, S_IFREG | mode);
+	if (IS_ERR(dentry))
+		return ERR_CAST(dentry);
+
+	if (d_really_is_negative(dentry)) {
+		error = -ENOENT;
+	} else if (!(file->f_mode & FMODE_OPENED)) {
+		struct path path = {.mnt = parent->mnt, .dentry = dentry };
+
+		error = vfs_open(&path, file);
+	}
+	dput(dentry);
+
+	if (error)
+		return ERR_PTR(error);
+	return no_free_ptr(file);
+}
+
 static inline bool trailing_slashes(struct nameidata *nd)
 {
 	return (bool)nd->last.name[nd->last.len];
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 2ad6dd9987b9..8c048c97a7f7 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -103,6 +103,9 @@ struct dentry *start_creating_dentry(struct dentry *parent,
 struct dentry *start_removing_dentry(struct dentry *parent,
 				     struct dentry *child);
 
+struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
+			     int open_flag, umode_t mode);
+
 /* end_creating - finish action started with start_creating
  * @child: dentry returned by start_creating() or vfs_mkdir()
  *
-- 
2.50.0.107.gf914562f5916.dirty