From 5100bdc814435a1222fef6438cebcd81a3de6c73 Mon Sep 17 00:00:00 2001
From: scosu <mpargmann@allfex.org>
Date: Thu, 13 Jun 2019 13:59:10 +0200
Subject: [PATCH 2/4] fuse_lowlevel: Add max_pages support (#384)

Starting with kernel version 4.20 fuse supports a new property
'max_pages' which is the maximum number of pages that can be used per
request. This can be set via an argument during initialization.
This new property allows writes to be larger than 128k.

This patch sets the property if the matching capability is set
(FUSE_MAX_PAGES). It will also set max_write to 1MiB. Filesystems have
the possibility to decrease this size by setting max_write to a smaller
size. The max_pages and bufsize fields are adjusted accordingly.

Cc: Constantine Shulyupin <const@MakeLinux.com>
Signed-off-by: Markus Pargmann <scosu@quobyte.com>
(cherry picked from commit 027d0d17c8a4605109f09d9c988e255b64a2c19a)
Signed-off-by: Pavel Reichl <preichl@redhat.com>
---
 ChangeLog.rst       |  7 +++++++
 lib/fuse_i.h        |  6 ++++++
 lib/fuse_lowlevel.c | 30 +++++++++++++++++++++---------
 3 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/ChangeLog.rst b/ChangeLog.rst
index 8ea9397..411cd4a 100644
--- a/ChangeLog.rst
+++ b/ChangeLog.rst
@@ -1,6 +1,13 @@
 libfuse 3.3.0 (2018-11-06)
 ==========================
 
+* Added support for fuse kernel feature `max_pages` which allows to increase
+  the maximum number of pages that can be used per request. This feature was
+  introduced in kernel 4.20. `max_pages` is set based on the value in
+  `max_write`. By default `max_write` will be 1MiB now for kernels that support
+  `max_pages`. If you want smaller buffers or writes you have to set
+  `max_write` manually.
+
 * The `auto_unmount` mode now works correctly in combination with
   autofs.
 
diff --git a/lib/fuse_i.h b/lib/fuse_i.h
index cf35551..d38b630 100644
--- a/lib/fuse_i.h
+++ b/lib/fuse_i.h
@@ -131,3 +131,9 @@ struct fuse *fuse_new_31(struct fuse_args *args, const struct fuse_operations *o
 int fuse_loop_mt_32(struct fuse *f, struct fuse_loop_config *config);
 int fuse_session_loop_mt_32(struct fuse_session *se, struct fuse_loop_config *config);
 
+#define FUSE_MAX_MAX_PAGES 256
+#define FUSE_DEFAULT_MAX_PAGES_PER_REQ 32
+
+/* room needed in buffer to accommodate header */
+#define FUSE_BUFFER_HEADER_SIZE 0x1000
+
diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
index 844e797..60195e0 100644
--- a/lib/fuse_lowlevel.c
+++ b/lib/fuse_lowlevel.c
@@ -1882,6 +1882,14 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 			se->conn.capable |= FUSE_CAP_POSIX_ACL;
 		if (arg->flags & FUSE_HANDLE_KILLPRIV)
 			se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV;
+		if (!(arg->flags & FUSE_MAX_PAGES)) {
+			size_t max_bufsize =
+				FUSE_DEFAULT_MAX_PAGES_PER_REQ * getpagesize()
+				+ FUSE_BUFFER_HEADER_SIZE;
+			if (bufsize > max_bufsize) {
+				bufsize = max_bufsize;
+			}
+		}
 	} else {
 		se->conn.max_readahead = 0;
 	}
@@ -1928,10 +1936,10 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 			bufsize);
 		bufsize = FUSE_MIN_READ_BUFFER;
 	}
+	se->bufsize = bufsize;
 
-	bufsize -= 4096;
-	if (bufsize < se->conn.max_write)
-		se->conn.max_write = bufsize;
+	if (se->conn.max_write > bufsize - FUSE_BUFFER_HEADER_SIZE)
+		se->conn.max_write = bufsize - FUSE_BUFFER_HEADER_SIZE;
 
 	se->got_init = 1;
 	if (se->op.init)
@@ -1958,6 +1966,14 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, const void *inarg)
 		return;
 	}
 
+	if (se->conn.max_write < bufsize - FUSE_BUFFER_HEADER_SIZE) {
+		se->bufsize = se->conn.max_write + FUSE_BUFFER_HEADER_SIZE;
+	}
+	if (arg->flags & FUSE_MAX_PAGES) {
+		outarg.flags |= FUSE_MAX_PAGES;
+		outarg.max_pages = (se->conn.max_write - 1) / getpagesize() + 1;
+	}
+
 	/* Always enable big writes, this is superseded
 	   by the max_write option */
 	outarg.flags |= FUSE_BIG_WRITES;
@@ -2779,11 +2795,6 @@ restart:
 	return res;
 }
 
-#define KERNEL_BUF_PAGES 32
-
-/* room needed in buffer to accommodate header */
-#define HEADER_SIZE 0x1000
-
 struct fuse_session *fuse_session_new(struct fuse_args *args,
 				      const struct fuse_lowlevel_ops *op,
 				      size_t op_size, void *userdata)
@@ -2844,7 +2855,8 @@ struct fuse_session *fuse_session_new(struct fuse_args *args,
 	if (se->debug)
 		fprintf(stderr, "FUSE library version: %s\n", PACKAGE_VERSION);
 
-	se->bufsize = KERNEL_BUF_PAGES * getpagesize() + HEADER_SIZE;
+	se->bufsize = FUSE_MAX_MAX_PAGES * getpagesize() +
+		FUSE_BUFFER_HEADER_SIZE;
 
 	list_init_req(&se->list);
 	list_init_req(&se->interrupts);
-- 
2.36.1