[PATCH 10/11] vfs: trylock inode->i_rwsem in iterate_dir() to support nowait

[Hao Xu]

From: Hao Xu <howeyxu@xxxxxxxxxxx>

Trylock inode->i_rwsem in iterate_dir() to support nowait semantics and
error out -EAGAIN when there is contention.

Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
---
 fs/readdir.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/readdir.c b/fs/readdir.c
index 6469f076ba6e..664ecd9665a1 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -43,6 +43,8 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
 	struct inode *inode = file_inode(file);
 	bool shared = false;
 	int res = -ENOTDIR;
+	bool nowait;
+
 	if (file->f_op->iterate_shared)
 		shared = true;
 	else if (!file->f_op->iterate)
@@ -52,16 +54,22 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
 	if (res)
 		goto out;
 
-	if (shared)
-		res = down_read_killable(&inode->i_rwsem);
-	else
-		res = down_write_killable(&inode->i_rwsem);
-	if (res)
+	nowait = ctx->flags & DIR_CONTEXT_F_NOWAIT;
+	if (nowait) {
+		res = shared ? down_read_trylock(&inode->i_rwsem) :
+			       down_write_trylock(&inode->i_rwsem);
+		if (!res)
+			res = -EAGAIN;
+	} else {
+		res = shared ? down_read_killable(&inode->i_rwsem) :
+			       down_write_killable(&inode->i_rwsem);
+	}
+	if (res < 0)
 		goto out;
 
 	res = -ENOENT;
 	if (!IS_DEADDIR(inode)) {
-		res = file_accessed(file, ctx->flags & DIR_CONTEXT_F_NOWAIT);
+		res = file_accessed(file, nowait);
 		if (res == -EAGAIN)
 			goto out_unlock;
 
-- 
2.25.1