[PATCH 4/7] vfs: change vfs_lookup_open() to return found dentry in path.dentry.

[NeilBrown <neilb@ownmail.net>]

From: NeilBrown <neil@brown.name>

The caller - nfsd - needs to know the type of object found when a
non-regular file was found to exist.  This is most easily done
by passing back the dentry.

So change calling pattern so that the path (now called "path") contains
the parent dentry on entry and the child dentry on exit.
vfs_lookup_open() will dput() the parent and caller must dput() the
child.

If lookup_open() returns -EFTYPE (from ->atomic_open()) we need to
use d_lookup() to find the dentry.  If ->atomic_open() didn't add a
dentry to the dcache we return %NULL in %path->dentry.

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/namei.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 0c787363b101..30ccc0c2f02f 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4606,7 +4606,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
 
 /**
  * vfs_lookup_open - open and possibly create a regular file
- * @parent: directory to contain file
+ * @path: directory to contain file
  * @last: final component of file name
  * @open_flag: O_flags
  * @mode: initial permissions for file
@@ -4619,9 +4619,15 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
  * If the fs object found is not a regular file then -EFTYPE is
  * returned.
  *
+ * @path is updated to contain the dentry that was found if possible.
+ * In particular, if -EFTYPE is returned, then @path.dentry will be the
+ * object that is not a regular file, or %NULL.
+ * Consequently the caller must be prepared for @path.dentry to be
+ * dput(), an it must dput() whatever is in @path.dentry after the call.
+ *
  * Returns: the opened struct file, or an error.
  */
-struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
+struct file *vfs_lookup_open(struct path *path, struct qstr *last,
 			     int open_flag, umode_t mode)
 {
 	struct file *file __free(fput) = NULL;
@@ -4638,7 +4644,7 @@ struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
 	mode |= S_IFREG;
 	open_flag |= __O_REGULAR;
 
-	error = lookup_noperm_common(last, parent->dentry);
+	error = lookup_noperm_common(last, path->dentry);
 	if (error)
 		return ERR_PTR(error);
 
@@ -4646,7 +4652,7 @@ struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
 	if (IS_ERR(file))
 		return file;
 
-	nd.path = *parent;
+	nd.path = *path;
 	nd.last = *last;
 	nd.flags = LOOKUP_OPEN;
 	if (open_flag & O_CREAT) {
@@ -4658,9 +4664,18 @@ struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
 	op.mode = mode;
 	dentry = lookup_open(&nd, file, &op);
 
-	if (IS_ERR(dentry))
+	if (IS_ERR(dentry)) {
+		if (dentry == -EFTYPE) {
+			/* Try to determine what was found */
+			struct dentry *child = d_lookup(path->dentry, &nd.last);
+			dput(path->dentry);
+			path->dentry = child;
+			WARN_ON_ONCE(child && d_is_reg(child));
+		}
 		return ERR_CAST(dentry);
-
+	}
+	dput(path->dentry);
+	path->dentry = dentry;
 	if (d_really_is_negative(dentry)) {
 		error = -ENOENT;
 	} else if (!(file->f_mode & FMODE_CREATED) && (open_flag & O_EXCL)) {
@@ -4668,10 +4683,8 @@ struct file *vfs_lookup_open(struct path *parent, struct qstr *last,
 	} else if (!d_is_reg(dentry)) {
 		error = -EFTYPE;
 	} else if (!(file->f_mode & FMODE_OPENED)) {
-		nd.path.dentry = dentry;
-		error = vfs_open(&nd.path, file);
+		error = vfs_open(path, file);
 	}
-	dput(dentry);
 
 	if (error)
 		return ERR_PTR(error);
-- 
2.50.0.107.gf914562f5916.dirty