From 926a414b90b4a2912bd03488e9f088dd6bca4199 Mon Sep 17 00:00:00 2001
From: Sergio Lopez <slp@redhat.com>
Date: Wed, 8 Apr 2020 11:23:02 +0200
Subject: [PATCH] vhost_user_fs: Add support for MAX_PAGES

Add support for MAX_PAGES, corresonding to FUSE_MAX_PAGES introduced
in FUSE 7.28.

This allows us to negotiate with the kernel the maximum number of
pages that we support to transfer in a single request.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 vhost_user_fs/src/fuse.rs   | 15 ++++++++++++++-
 vhost_user_fs/src/server.rs |  8 +++++++-
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/vhost_user_fs/src/fuse.rs b/vhost_user_fs/src/fuse.rs
index 98401b073..9e86fc325 100644
--- a/vhost_user_fs/src/fuse.rs
+++ b/vhost_user_fs/src/fuse.rs
@@ -137,6 +137,9 @@ const POSIX_ACL: u32 = 1_048_576;
 /// Reading the device after abort returns ECONNABORTED.
 const ABORT_ERROR: u32 = 2_097_152;
 
+/// Init_out.max_pages contains the max number of req pages.
+const MAX_PAGES: u32 = 4_194_304;
+
 bitflags! {
     /// A bitfield passed in as a parameter to and returned from the `init` method of the
     /// `FileSystem` trait.
@@ -309,6 +312,14 @@ bitflags! {
         ///
         /// This feature is not currently supported.
         const ABORT_ERROR = ABORT_ERROR;
+
+        /// Indicates support for negotiating the maximum number of pages supported.
+        ///
+        /// If this feature is enabled, we can tell the kernel the maximum number of pages that we
+        /// support to transfer in a single request.
+        ///
+        /// This feature is enabled by default if supported by the kernel.
+        const MAX_PAGES = MAX_PAGES;
     }
 }
 
@@ -848,7 +859,9 @@ pub struct InitOut {
     pub congestion_threshold: u16,
     pub max_write: u32,
     pub time_gran: u32,
-    pub unused: [u32; 9],
+    pub max_pages: u16,
+    pub padding: u16,
+    pub unused: [u32; 8],
 }
 unsafe impl ByteValued for InitOut {}
 
diff --git a/vhost_user_fs/src/server.rs b/vhost_user_fs/src/server.rs
index 4c2242140..2ac8f8f30 100644
--- a/vhost_user_fs/src/server.rs
+++ b/vhost_user_fs/src/server.rs
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+use std::convert::TryInto;
 use std::ffi::CStr;
 use std::fs::File;
 use std::io::{self, Read, Write};
@@ -903,10 +904,14 @@ impl<F: FileSystem + Sync> Server<F> {
             | FsOptions::HANDLE_KILLPRIV
             | FsOptions::ASYNC_DIO
             | FsOptions::HAS_IOCTL_DIR
-            | FsOptions::ATOMIC_O_TRUNC;
+            | FsOptions::ATOMIC_O_TRUNC
+            | FsOptions::MAX_PAGES;
 
         let capable = FsOptions::from_bits_truncate(flags);
 
+        let page_size: u32 = unsafe { libc::sysconf(libc::_SC_PAGESIZE).try_into().unwrap() };
+        let max_pages = ((MAX_BUFFER_SIZE - 1) / page_size) + 1;
+
         match self.fs.init(capable) {
             Ok(want) => {
                 let enabled = capable & (want | supported);
@@ -920,6 +925,7 @@ impl<F: FileSystem + Sync> Server<F> {
                     congestion_threshold: (::std::u16::MAX / 4) * 3,
                     max_write: MAX_BUFFER_SIZE,
                     time_gran: 1, // nanoseconds
+                    max_pages: max_pages.try_into().unwrap(),
                     ..Default::default()
                 };