Refactor FUSE connection for readability and structure

This change decouples the code that is weakly
tied to the connection struct from connection.go,
rename variables and files with more meaningful choices,
adds detailed comments, explains lock orders,
and adds other minor improvement to make
the existing FUSE code more readable and
more organized.

Purpose is to avoid too much code in one file
and provide better structure for the
future commits.

1 files changed, 183 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/fuse/connection_control.go b/pkg/sentry/fsimpl/fuse/connection_control.go
new file mode 100644
index 000000000..d84d9caf2
--- /dev/null
+++ b/pkg/sentry/fsimpl/fuse/connection_control.go
@@ -0,0 +1,183 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fuse
+
+import (
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+)
+
+// consts used by FUSE_INIT negotiation.
+const (
+	// fuseMaxMaxPages is the maximum value for MaxPages received in InitOut.
+	// Follow the same behavior as unix fuse implementation.
+	fuseMaxMaxPages = 256
+
+	// Maximum value for the time granularity for file time stamps, 1s.
+	// Follow the same behavior as unix fuse implementation.
+	fuseMaxTimeGranNs = 1000000000
+
+	// Minimum value for MaxWrite and MaxRead.
+	// Follow the same behavior as unix fuse implementation.
+	fuseMinMaxWrite = 4096
+	fuseMinMaxRead  = 4096
+
+	// Temporary default value for max readahead, 128kb.
+	fuseDefaultMaxReadahead = 131072
+
+	// The FUSE_INIT_IN flags sent to the daemon.
+	// TODO(gvisor.dev/issue/3199): complete the flags.
+	fuseDefaultInitFlags = linux.FUSE_MAX_PAGES
+)
+
+// Adjustable maximums for Connection's cogestion control parameters.
+// Used as the upperbound of the config values.
+// Currently we do not support adjustment to them.
+var (
+	MaxUserBackgroundRequest   uint16 = fuseDefaultMaxBackground
+	MaxUserCongestionThreshold uint16 = fuseDefaultCongestionThreshold
+)
+
+// SetInitialized atomically sets the connection as initialized.
+func (conn *connection) SetInitialized() {
+	// Unblock the requests sent before INIT.
+	close(conn.initializedChan)
+
+	// Close the channel first to avoid the non-atomic situation
+	// where conn.initialized is true but there are
+	// tasks being blocked on the channel.
+	// And it prevents the newer tasks from gaining
+	// unnecessary higher chance to be issued before the blocked one.
+
+	atomic.StoreInt32(&(conn.initialized), int32(1))
+}
+
+// IsInitialized atomically check if the connection is initialized.
+// pairs with SetInitialized().
+func (conn *connection) Initialized() bool {
+	return atomic.LoadInt32(&(conn.initialized)) != 0
+}
+
+// InitSend sends a FUSE_INIT request.
+func (conn *connection) InitSend(creds *auth.Credentials, pid uint32) error {
+	in := linux.FUSEInitIn{
+		Major: linux.FUSE_KERNEL_VERSION,
+		Minor: linux.FUSE_KERNEL_MINOR_VERSION,
+		// TODO(gvisor.dev/issue/3196): find appropriate way to calculate this
+		MaxReadahead: fuseDefaultMaxReadahead,
+		Flags:        fuseDefaultInitFlags,
+	}
+
+	req, err := conn.NewRequest(creds, pid, 0, linux.FUSE_INIT, &in)
+	if err != nil {
+		return err
+	}
+
+	// Since there is no task to block on and FUSE_INIT is the request
+	// to unblock other requests, use nil.
+	return conn.CallAsync(nil, req)
+}
+
+// InitRecv receives a FUSE_INIT reply and process it.
+func (conn *connection) InitRecv(res *Response, hasSysAdminCap bool) error {
+	if err := res.Error(); err != nil {
+		return err
+	}
+
+	initRes := fuseInitRes{initLen: res.DataLen()}
+	if err := res.UnmarshalPayload(&initRes); err != nil {
+		return err
+	}
+
+	return conn.initProcessReply(&initRes.initOut, hasSysAdminCap)
+}
+
+// Process the FUSE_INIT reply from the FUSE server.
+// It tries to acquire the conn.asyncMu lock if minor version is newer than 13.
+func (conn *connection) initProcessReply(out *linux.FUSEInitOut, hasSysAdminCap bool) error {
+	// No matter error or not, always set initialzied.
+	// to unblock the blocked requests.
+	defer conn.SetInitialized()
+
+	// No support for old major fuse versions.
+	if out.Major != linux.FUSE_KERNEL_VERSION {
+		conn.connInitError = true
+		return nil
+	}
+
+	// Start processing the reply.
+	conn.connInitSuccess = true
+	conn.minor = out.Minor
+
+	// No support for negotiating MaxWrite before minor version 5.
+	if out.Minor >= 5 {
+		conn.maxWrite = out.MaxWrite
+	} else {
+		conn.maxWrite = fuseMinMaxWrite
+	}
+	if conn.maxWrite < fuseMinMaxWrite {
+		conn.maxWrite = fuseMinMaxWrite
+	}
+
+	// No support for the following flags before minor version 6.
+	if out.Minor >= 6 {
+		conn.asyncRead = out.Flags&linux.FUSE_ASYNC_READ != 0
+		conn.bigWrites = out.Flags&linux.FUSE_BIG_WRITES != 0
+		conn.dontMask = out.Flags&linux.FUSE_DONT_MASK != 0
+		conn.writebackCache = out.Flags&linux.FUSE_WRITEBACK_CACHE != 0
+
+		// TODO(gvisor.dev/issue/3195): figure out how to use TimeGran (0 < TimeGran <= fuseMaxTimeGranNs).
+
+		if out.Flags&linux.FUSE_MAX_PAGES != 0 {
+			maxPages := out.MaxPages
+			if maxPages < 1 {
+				maxPages = 1
+			}
+			if maxPages > fuseMaxMaxPages {
+				maxPages = fuseMaxMaxPages
+			}
+			conn.maxPages = maxPages
+		}
+	}
+
+	// No support for limits before minor version 13.
+	if out.Minor >= 13 {
+		conn.asyncMu.Lock()
+
+		if out.MaxBackground > 0 {
+			conn.asyncNumMax = out.MaxBackground
+
+			if !hasSysAdminCap &&
+				conn.asyncNumMax > MaxUserBackgroundRequest {
+				conn.asyncNumMax = MaxUserBackgroundRequest
+			}
+		}
+
+		if out.CongestionThreshold > 0 {
+			conn.asyncCongestionThreshold = out.CongestionThreshold
+
+			if !hasSysAdminCap &&
+				conn.asyncCongestionThreshold > MaxUserCongestionThreshold {
+				conn.asyncCongestionThreshold = MaxUserCongestionThreshold
+			}
+		}
+
+		conn.asyncMu.Unlock()
+	}
+
+	return nil
+}