[PATCH v2 4/6] kernfs: implement readdir FMODE_NOWAIT

[Dominique Martinet <asmadeus@codewreck.org>]

Since down_read can block, use the _trylock variant if NOWAIT variant
has been requested.
(can probably do a little bit better style-wise)

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
---
 fs/kernfs/dir.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 45b6919903e6..5a5b3e7881bf 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1824,7 +1824,12 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
 		return 0;
 
 	root = kernfs_root(parent);
-	down_read(&root->kernfs_rwsem);
+	if (ctx->flags & DIR_CONTEXT_F_NOWAIT) {
+		if (!down_read_trylock(&root->kernfs_rwsem))
+			return -EAGAIN;
+	} else {
+		down_read(&root->kernfs_rwsem);
+	}
 
 	if (kernfs_ns_enabled(parent))
 		ns = kernfs_info(dentry->d_sb)->ns;
@@ -1845,6 +1850,12 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
 		if (!dir_emit(ctx, name, len, ino, type))
 			return 0;
 		down_read(&root->kernfs_rwsem);
+		if (ctx->flags & DIR_CONTEXT_F_NOWAIT) {
+			if (!down_read_trylock(&root->kernfs_rwsem))
+				return 0;
+		} else {
+			down_read(&root->kernfs_rwsem);
+		}
 	}
 	up_read(&root->kernfs_rwsem);
 	file->private_data = NULL;
@@ -1852,7 +1863,14 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
 	return 0;
 }
 
+static int kernfs_fop_dir_open(struct inode *inode, struct file *file)
+{
+	file->f_mode |= FMODE_NOWAIT;
+	return 0;
+}
+
 const struct file_operations kernfs_dir_fops = {
+	.open		= kernfs_fop_dir_open,
 	.read		= generic_read_dir,
 	.iterate_shared	= kernfs_fop_readdir,
 	.release	= kernfs_dir_fop_release,

-- 
2.39.2