From 3017a895474a6b36aa385eb27fd156f72d5360f2 Mon Sep 17 00:00:00 2001
From: Anagh Kumar Baranwal <6824881+darthShadow@users.noreply.github.com>
Date: Mon, 10 Feb 2020 10:24:33 +0530
Subject: [PATCH] Added support for Max Pages, which was introduced from Linux
 Kernel 4.20

Signed-off-by: Anagh Kumar Baranwal <6824881+darthShadow@users.noreply.github.com>
---
 fuse.go            | 18 +++++++++++++++++-
 fuse_kernel.go     |  4 ++++
 fuse_linux.go      |  4 +++-
 options.go         |  9 +++++++++
 options_darwin.go  |  4 ++++
 options_freebsd.go |  4 ++++
 options_linux.go   | 12 ++++++++++++
 7 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/fuse.go b/fuse.go
index b774a25c..6340df4b 100644
--- a/fuse.go
+++ b/fuse.go
@@ -156,7 +156,8 @@ func (e *MountpointDoesNotExistError) Error() string {
 // progress.
 func Mount(dir string, options ...MountOption) (*Conn, error) {
 	conf := mountConfig{
-		options: make(map[string]string),
+		options:  make(map[string]string),
+		maxPages: 32,
 	}
 	for _, option := range options {
 		if err := option(&conf); err != nil {
@@ -238,10 +239,20 @@ func initMount(c *Conn, conf *mountConfig) error {
 		MaxWrite:     maxWrite,
 		Flags:        InitBigWrites | conf.initFlags,
 	}
+
+	setMaxPages(r, s, conf)
+
 	r.Respond(s)
 	return nil
 }
 
+func setMaxPages(request *InitRequest, response *InitResponse, conf *mountConfig) {
+	if (request.Flags & InitMaxPages) == InitMaxPages {
+		response.Flags |= InitMaxPages
+		response.MaxPages = conf.maxPages
+	}
+}
+
 // A Request represents a single FUSE request received from the kernel.
 // Use a type switch to determine the specific kind.
 // A request of unrecognized type will have concrete type *Header.
@@ -1249,6 +1260,9 @@ type InitResponse struct {
 	// Maximum size of a single write operation.
 	// Linux enforces a minimum of 4 KiB.
 	MaxWrite uint32
+	// Maximum number of pages in a single write operation.
+	// Linux enforces a minimum of 32.
+	MaxPages uint16
 }
 
 func (r *InitResponse) String() string {
@@ -1264,12 +1278,14 @@ func (r *InitRequest) Respond(resp *InitResponse) {
 	out.MaxReadahead = resp.MaxReadahead
 	out.Flags = uint32(resp.Flags)
 	out.MaxWrite = resp.MaxWrite
+	out.MaxPages = resp.MaxPages
 
 	// MaxWrite larger than our receive buffer would just lead to
 	// errors on large writes.
 	if out.MaxWrite > maxWrite {
 		out.MaxWrite = maxWrite
 	}
+
 	r.respond(buf)
 }
 
diff --git a/fuse_kernel.go b/fuse_kernel.go
index 416d32aa..68fc123a 100644
--- a/fuse_kernel.go
+++ b/fuse_kernel.go
@@ -274,6 +274,8 @@ const (
 	InitWritebackCache  InitFlags = 1 << 16
 	InitNoOpenSupport   InitFlags = 1 << 17
 
+	InitMaxPages InitFlags = 1 << 22 // Linux only
+
 	InitCaseSensitive InitFlags = 1 << 29 // OS X only
 	InitVolRename     InitFlags = 1 << 30 // OS X only
 	InitXtimes        InitFlags = 1 << 31 // OS X only
@@ -708,6 +710,8 @@ type initOut struct {
 	Flags        uint32
 	Unused       uint32
 	MaxWrite     uint32
+	_            uint32 // Unused, refers to TimeGran
+	MaxPages     uint16
 }
 
 type interruptIn struct {
diff --git a/fuse_linux.go b/fuse_linux.go
index 5fb96f9a..a1e414b1 100644
--- a/fuse_linux.go
+++ b/fuse_linux.go
@@ -4,4 +4,6 @@ package fuse
 //
 // Linux 4.2.0 has been observed to cap this value at 128kB
 // (FUSE_MAX_PAGES_PER_REQ=32, 4kB pages).
-const maxWrite = 128 * 1024
+// From Linux 4.20, the cap has been increased to 1MiB
+// (FUSE_MAX_PAGES_PER_REQ=256, 4kB pages).
+const maxWrite = 1 * 1024 * 1024 // 1 MiB
diff --git a/options.go b/options.go
index f09ffd4e..4bb7483c 100644
--- a/options.go
+++ b/options.go
@@ -16,6 +16,7 @@ type mountConfig struct {
 	maxReadahead     uint32
 	initFlags        InitFlags
 	osxfuseLocations []OSXFUSEPaths
+	maxPages         uint16
 }
 
 func escapeComma(s string) string {
@@ -294,3 +295,11 @@ func AllowNonEmptyMount() MountOption {
 		return nil
 	}
 }
+
+// EnableMaxPages enables the configuration of the maximum number of pages
+// in the request & response from the kernel.
+//
+// Linux only. Others ignore this option.
+func MaxPages(count uint16) MountOption {
+	return maxPages(count)
+}
diff --git a/options_darwin.go b/options_darwin.go
index a85e64cb..f82faa58 100644
--- a/options_darwin.go
+++ b/options_darwin.go
@@ -38,3 +38,7 @@ func noBrowse(conf *mountConfig) error {
 	conf.options["nobrowse"] = ""
 	return nil
 }
+
+func maxPages(count uint16) MountOption {
+	return dummyOption
+}
diff --git a/options_freebsd.go b/options_freebsd.go
index 2c956e7f..e62f9c6f 100644
--- a/options_freebsd.go
+++ b/options_freebsd.go
@@ -30,3 +30,7 @@ func exclCreate(conf *mountConfig) error {
 func noBrowse(conf *mountConfig) error {
 	return nil
 }
+
+func maxPages(count uint16) MountOption {
+	return dummyOption
+}
diff --git a/options_linux.go b/options_linux.go
index 2c925b18..510cc8c7 100644
--- a/options_linux.go
+++ b/options_linux.go
@@ -27,3 +27,15 @@ func exclCreate(conf *mountConfig) error {
 func noBrowse(conf *mountConfig) error {
 	return nil
 }
+
+func maxPages(count uint16) MountOption {
+	return func(conf *mountConfig) error {
+		if count < 32 {
+			count = 32 // The minimum allowed by the kernel
+		} else if count > 256 {
+			count = 256 // The maximum allowed by the kernel
+		}
+		conf.maxPages = count
+		return nil
+	}
+}