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// Copyright 2021 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 lisafs
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/sync"
)
// Server serves a filesystem tree. Multiple connections on different mount
// points can be started on a server. The server provides utilities to safely
// modify the filesystem tree across its connections (mount points). Note that
// it does not support synchronizing filesystem tree mutations across other
// servers serving the same filesystem subtree. Server also manages the
// lifecycle of all connections.
type Server struct {
// connWg counts the number of active connections being tracked.
connWg sync.WaitGroup
// renameMu synchronizes rename operations within this filesystem tree.
renameMu sync.RWMutex
// handlers is a list of RPC handlers which can be indexed by the handler's
// corresponding MID.
handlers []RPCHandler
// root is the root of the filesystem tree being managed by this server.
// root is immutable. Server holds a ref on root for its entire lifetime.
root *Node
// impl is the server implementation which embeds this server.
impl ServerImpl
// opts is the server specific options. This dictates how some of the
// messages are handled.
opts ServerOpts
}
// ServerOpts defines some server implementation specific behavior.
type ServerOpts struct {
// WalkStatSupported is set to true if it's safe to call
// ControlFDImpl.WalkStat and let the file implementation perform the walk
// without holding locks on any of the descendant's Nodes.
WalkStatSupported bool
// SetAttrOnDeleted is set to true if it's safe to call ControlFDImpl.SetStat
// for deleted files.
SetAttrOnDeleted bool
// AllocateOnDeleted is set to true if it's safe to call OpenFDImpl.Allocate
// for deleted files.
AllocateOnDeleted bool
}
// Init must be called before first use of server.
func (s *Server) Init(impl ServerImpl, opts ServerOpts) {
s.impl = impl
s.opts = opts
s.handlers = handlers[:]
s.root = &Node{}
// s owns the ref on s.root.
s.root.InitLocked("", nil)
}
// SetHandlers overrides the server's RPC handlers. Mainly should only be used
// for tests.
func (s *Server) SetHandlers(handlers []RPCHandler) {
s.handlers = handlers
}
// withRenameReadLock invokes fn with the server's rename mutex locked for
// reading. This ensures that no rename operations occur concurrently.
func (s *Server) withRenameReadLock(fn func() error) error {
s.renameMu.RLock()
defer s.renameMu.RUnlock()
return fn()
}
// StartConnection starts the connection on a separate goroutine and tracks it.
func (s *Server) StartConnection(c *Connection) {
s.connWg.Add(1)
go func() {
c.Run()
s.connWg.Done()
}()
}
// Wait waits for all connections started via StartConnection() to terminate.
func (s *Server) Wait() {
s.connWg.Wait()
}
// Destroy releases resources being used by this server.
func (s *Server) Destroy() {
s.root.DecRef(nil)
}
// ServerImpl contains the implementation details for a Server.
// Implementations of ServerImpl should contain their associated Server by
// value as their first field.
type ServerImpl interface {
// Mount is called when a Mount RPC is made. It mounts the connection on
// mountNode.
//
// Mount has a read concurrency guarantee on mountNode.
Mount(c *Connection, mountNode *Node) (*ControlFD, linux.Statx, error)
// SupportedMessages returns a list of messages that the server
// implementation supports.
SupportedMessages() []MID
// MaxMessageSize is the maximum payload length (in bytes) that can be sent
// to this server implementation.
MaxMessageSize() uint32
}
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