fuse: enable caching of symlinks

FUSE file reads are cached in the page cache, but symlink reads are
not. This patch enables FUSE READLINK operations to be cached which
can improve performance of some FUSE workloads.

In particular, I'm working on a FUSE filesystem for access to source
code and discovered that about a 10% improvement to build times is
achieved with this patch (there are a lot of symlinks in the source
tree).

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 83 insertions, 25 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 7b8f63e7489f..47395b0c3b35 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1160,38 +1160,78 @@ static int fuse_permission(struct inode *inode, int mask)
 	return err;
 }
 
-static const char *fuse_get_link(struct dentry *dentry,
-				 struct inode *inode,
-				 struct delayed_call *done)
+static int fuse_readlink_page(struct inode *inode, struct page *page)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	FUSE_ARGS(args);
-	char *link;
-	ssize_t ret;
+	struct fuse_req *req;
+	int err;
 
-	if (!dentry)
-		return ERR_PTR(-ECHILD);
+	req = fuse_get_req(fc, 1);
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	req->out.page_zeroing = 1;
+	req->out.argpages = 1;
+	req->num_pages = 1;
+	req->pages[0] = page;
+	req->page_descs[0].length = PAGE_SIZE - 1;
+	req->in.h.opcode = FUSE_READLINK;
+	req->in.h.nodeid = get_node_id(inode);
+	req->out.argvar = 1;
+	req->out.numargs = 1;
+	req->out.args[0].size = PAGE_SIZE - 1;
+	fuse_request_send(fc, req);
+	err = req->out.h.error;
 
-	link = kmalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!link)
-		return ERR_PTR(-ENOMEM);
+	if (!err) {
+		char *link = page_address(page);
+		size_t len = req->out.args[0].size;
 
-	args.in.h.opcode = FUSE_READLINK;
-	args.in.h.nodeid = get_node_id(inode);
-	args.out.argvar = 1;
-	args.out.numargs = 1;
-	args.out.args[0].size = PAGE_SIZE - 1;
-	args.out.args[0].value = link;
-	ret = fuse_simple_request(fc, &args);
-	if (ret < 0) {
-		kfree(link);
-		link = ERR_PTR(ret);
-	} else {
-		link[ret] = '\0';
-		set_delayed_call(done, kfree_link, link);
+		BUG_ON(len >= PAGE_SIZE);
+		link[len] = '\0';
 	}
+
+	fuse_put_request(fc, req);
 	fuse_invalidate_atime(inode);
-	return link;
+
+	return err;
+}
+
+static const char *fuse_get_link(struct dentry *dentry, struct inode *inode,
+				 struct delayed_call *callback)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct page *page;
+	int err;
+
+	err = -EIO;
+	if (is_bad_inode(inode))
+		goto out_err;
+
+	if (fc->cache_symlinks)
+		return page_get_link(dentry, inode, callback);
+
+	err = -ECHILD;
+	if (!dentry)
+		goto out_err;
+
+	page = alloc_page(GFP_KERNEL);
+	err = -ENOMEM;
+	if (!page)
+		goto out_err;
+
+	err = fuse_readlink_page(inode, page);
+	if (err) {
+		__free_page(page);
+		goto out_err;
+	}
+
+	set_delayed_call(callback, page_put_link, page);
+
+	return page_address(page);
+
+out_err:
+	return ERR_PTR(err);
 }
 
 static int fuse_dir_open(struct inode *inode, struct file *file)
@@ -1644,7 +1684,25 @@ void fuse_init_dir(struct inode *inode)
 	fi->rdc.version = 0;
 }
 
+static int fuse_symlink_readpage(struct file *null, struct page *page)
+{
+	int err = fuse_readlink_page(page->mapping->host, page);
+
+	if (!err)
+		SetPageUptodate(page);
+
+	unlock_page(page);
+
+	return err;
+}
+
+static const struct address_space_operations fuse_symlink_aops = {
+	.readpage	= fuse_symlink_readpage,
+};
+
 void fuse_init_symlink(struct inode *inode)
 {
 	inode->i_op = &fuse_symlink_inode_operations;
+	inode->i_data.a_ops = &fuse_symlink_aops;
+	inode_nohighmem(inode);
 }