From 96658124d7a806ad833be3de9ffd1fb121811145 Mon Sep 17 00:00:00 2001
From: Alan Somers <asomers@FreeBSD.org>
Date: Mon, 13 May 2019 23:30:06 +0000
Subject: [PATCH] fusefs: eliminate superfluous FUSE_GETATTR when filesize=0

fuse_vnode_refreshsize was using 0 as a flag value for filesize meaning
"uninitialized" (thanks to the malloc(...M_ZERO) in fuse_vnode_alloc.  But
this led to unnecessary getattr operations when the filesize legitimately
happened to be zero.  Fix by adding a distinct flag value.

Sponsored by:	The FreeBSD Foundation
---
 sys/fs/fuse/fuse_node.c | 10 +++-------
 sys/fs/fuse/fuse_node.h |  8 +++++++-
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/sys/fs/fuse/fuse_node.c b/sys/fs/fuse/fuse_node.c
index 2c6fe6f86ce6..83b93f2a255c 100644
--- a/sys/fs/fuse/fuse_node.c
+++ b/sys/fs/fuse/fuse_node.c
@@ -143,6 +143,7 @@ fuse_vnode_init(struct vnode *vp, struct fuse_vnode_data *fvdat,
 	fvdat->nid = nodeid;
 	LIST_INIT(&fvdat->handles);
 	vattr_null(&fvdat->cached_attrs);
+	fvdat->filesize = FUSE_FILESIZE_UNINITIALIZED;
 	if (nodeid == FUSE_ROOT_ID) {
 		vp->v_vflag |= VV_ROOT;
 	}
@@ -388,15 +389,10 @@ fuse_vnode_refreshsize(struct vnode *vp, struct ucred *cred)
 
 	if ((fvdat->flag & FN_SIZECHANGE) != 0 ||
 	    fuse_data_cache_mode == FUSE_CACHE_UC ||
-	    fvdat->filesize != 0)
+	    fvdat->filesize != FUSE_FILESIZE_UNINITIALIZED)
 		return 0;
 
-	/*
-	 * TODO: replace VOP_GETATTR with fuse_internal_getattr to use the
-	 * cached attributes.  Better yet, replace fvdat->filesize with
-	 * attrs->va_size
-	 */
-	err = VOP_GETATTR(vp, &va, cred);
+	err = fuse_internal_getattr(vp, &va, cred, curthread);
 	SDT_PROBE2(fusefs, , node, trace, 1, "refreshed file size");
 	return err;
 }
diff --git a/sys/fs/fuse/fuse_node.h b/sys/fs/fuse/fuse_node.h
index 315635d55db3..8e7500d24fe7 100644
--- a/sys/fs/fuse/fuse_node.h
+++ b/sys/fs/fuse/fuse_node.h
@@ -71,6 +71,8 @@
 #define FN_SIZECHANGE        0x00000100
 #define FN_DIRECTIO          0x00000200
 
+#define FUSE_FILESIZE_UNINITIALIZED	-1
+
 struct fuse_vnode_data {
 	/** self **/
 	uint64_t	nid;
@@ -89,7 +91,11 @@ struct fuse_vnode_data {
 	/* The monotonic time after which the attr cache is invalid */
 	struct bintime	attr_cache_timeout;
 	struct vattr	cached_attrs;
-	/* TODO: use cached_attrs.size instead */
+	/*
+	 * File size according to the kernel, not the daemon.
+	 * May differ from cached_attrs.st_size due to write caching.  Unlike
+	 * cached_attrs.st_size, filesize never expires.
+	 */
 	off_t		filesize;
 	uint64_t	nlookup;
 	enum vtype	vtype;