[PATCH 3/3] virtiofs: Add negative_dentry_timeout option

[Keiichi Watanabe <keiichiw@chromium.org>]

Add negative_dentry_timeout mount option to virtiofs to caching negative
dentry on the guest side. When the host virito-fs device has an exclusive
access to the file system and the machine has enough memory, one can
specify a long time as the timeout.

This option saves ~1 second per 10,000 stat request for non-existing paths.

Signed-off-by: Keiichi Watanabe <keiichiw@chromium.org>
---

 Documentation/filesystems/virtiofs.rst | 4 ++++
 fs/fuse/virtio_fs.c                    | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/Documentation/filesystems/virtiofs.rst b/Documentation/filesystems/virtiofs.rst
index fdec5a7840f7..b045ef2223de 100644
--- a/Documentation/filesystems/virtiofs.rst
+++ b/Documentation/filesystems/virtiofs.rst
@@ -48,6 +48,10 @@ ro, rw, context, etc. Also, virtiofs has its own options.
 dax[=always,never,inode]
   Enable direct access for files. See :ref:`virtiofs-dax`.
 
+negative_dentry_timeout=N
+  Set the time in seconds to keep negative dentry cache. Same as the FUSE's
+  mount option.
+
 atime behavior
 ^^^^^^^^^^^^^^
 
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 4d8d4f16c727..bbbd840510f9 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -99,11 +99,13 @@ static const struct constant_table dax_param_enums[] = {
 enum {
 	OPT_DAX,
 	OPT_DAX_ENUM,
+	OPT_NEGATIVE_DENTRY_TIMEOUT,
 };
 
 static const struct fs_parameter_spec virtio_fs_parameters[] = {
 	fsparam_flag("dax", OPT_DAX),
 	fsparam_enum("dax", OPT_DAX_ENUM, dax_param_enums),
+	fsparam_u32 ("negative_dentry_timeout", OPT_NEGATIVE_DENTRY_TIMEOUT),
 	{}
 };
 
@@ -125,6 +127,9 @@ static int virtio_fs_parse_param(struct fs_context *fsc,
 	case OPT_DAX_ENUM:
 		ctx->dax_mode = result.uint_32;
 		break;
+	case OPT_NEGATIVE_DENTRY_TIMEOUT:
+		ctx->negative_dentry_timeout = result.uint_32;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -1416,6 +1421,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
 	struct super_block *sb;
 	struct fuse_conn *fc = NULL;
 	struct fuse_mount *fm;
+	struct fuse_fs_context *ffc;
 	unsigned int virtqueue_size;
 	int err = -EIO;
 
@@ -1468,6 +1474,8 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
 
 		sb->s_flags |= SB_ACTIVE;
 	}
+	ffc = fsc->fs_private;
+	fm->negative_dentry_timeout = ffc->negative_dentry_timeout;
 
 	WARN_ON(fsc->root);
 	fsc->root = dget(sb->s_root);
-- 
2.41.0.185.g7c58973941-goog