308 lines
8.0 KiB
Go
308 lines
8.0 KiB
Go
// Copyright 2018 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package p9
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import (
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"errors"
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"fmt"
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"sync"
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"syscall"
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"gvisor.googlesource.com/gvisor/pkg/log"
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"gvisor.googlesource.com/gvisor/pkg/unet"
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)
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// ErrOutOfTags indicates no tags are available.
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var ErrOutOfTags = errors.New("out of tags -- messages lost?")
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// ErrOutOfFIDs indicates no more FIDs are available.
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var ErrOutOfFIDs = errors.New("out of FIDs -- messages lost?")
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// ErrUnexpectedTag indicates a response with an unexpected tag was received.
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var ErrUnexpectedTag = errors.New("unexpected tag in response")
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// ErrVersionsExhausted indicates that all versions to negotiate have been exhausted.
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var ErrVersionsExhausted = errors.New("exhausted all versions to negotiate")
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// ErrBadVersionString indicates that the version string is malformed or unsupported.
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var ErrBadVersionString = errors.New("bad version string")
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// ErrBadResponse indicates the response didn't match the request.
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type ErrBadResponse struct {
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Got MsgType
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Want MsgType
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}
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// Error returns a highly descriptive error.
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func (e *ErrBadResponse) Error() string {
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return fmt.Sprintf("unexpected message type: got %v, want %v", e.Got, e.Want)
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}
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// response is the asynchronous return from recv.
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//
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// This is used in the pending map below.
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type response struct {
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r message
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done chan error
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}
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var responsePool = sync.Pool{
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New: func() interface{} {
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return &response{
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done: make(chan error, 1),
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}
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},
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}
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// Client is at least a 9P2000.L client.
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type Client struct {
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// socket is the connected socket.
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socket *unet.Socket
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// tagPool is the collection of available tags.
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tagPool pool
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// fidPool is the collection of available fids.
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fidPool pool
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// pending is the set of pending messages.
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pending map[Tag]*response
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pendingMu sync.Mutex
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// sendMu is the lock for sending a request.
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sendMu sync.Mutex
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// recvr is essentially a mutex for calling recv.
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//
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// Whoever writes to this channel is permitted to call recv. When
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// finished calling recv, this channel should be emptied.
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recvr chan bool
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// messageSize is the maximum total size of a message.
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messageSize uint32
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// payloadSize is the maximum payload size of a read or write
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// request. For large reads and writes this means that the
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// read or write is broken up into buffer-size/payloadSize
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// requests.
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payloadSize uint32
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// version is the agreed upon version X of 9P2000.L.Google.X.
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// version 0 implies 9P2000.L.
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version uint32
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}
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// NewClient creates a new client. It performs a Tversion exchange with
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// the server to assert that messageSize is ok to use.
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//
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// You should not use the same socket for multiple clients.
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func NewClient(socket *unet.Socket, messageSize uint32, version string) (*Client, error) {
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// Need at least one byte of payload.
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if messageSize <= msgRegistry.largestFixedSize {
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return nil, &ErrMessageTooLarge{
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size: messageSize,
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msize: msgRegistry.largestFixedSize,
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}
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}
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// Compute a payload size and round to 512 (normal block size)
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// if it's larger than a single block.
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payloadSize := messageSize - msgRegistry.largestFixedSize
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if payloadSize > 512 && payloadSize%512 != 0 {
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payloadSize -= (payloadSize % 512)
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}
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c := &Client{
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socket: socket,
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tagPool: pool{start: 1, limit: uint64(NoTag)},
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fidPool: pool{start: 1, limit: uint64(NoFID)},
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pending: make(map[Tag]*response),
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recvr: make(chan bool, 1),
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messageSize: messageSize,
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payloadSize: payloadSize,
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}
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// Agree upon a version.
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requested, ok := parseVersion(version)
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if !ok {
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return nil, ErrBadVersionString
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}
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for {
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rversion := Rversion{}
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err := c.sendRecv(&Tversion{Version: versionString(requested), MSize: messageSize}, &rversion)
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// The server told us to try again with a lower version.
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if err == syscall.EAGAIN {
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if requested == lowestSupportedVersion {
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return nil, ErrVersionsExhausted
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}
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requested--
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continue
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}
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// We requested an impossible version or our other parameters were bogus.
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if err != nil {
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return nil, err
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}
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// Parse the version.
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version, ok := parseVersion(rversion.Version)
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if !ok {
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// The server gave us a bad version. We return a generically worrisome error.
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log.Warningf("server returned bad version string %q", rversion.Version)
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return nil, ErrBadVersionString
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}
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c.version = version
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break
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}
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return c, nil
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}
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// handleOne handles a single incoming message.
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//
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// This should only be called with the token from recvr. Note that the received
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// tag will automatically be cleared from pending.
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func (c *Client) handleOne() {
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tag, r, err := recv(c.socket, c.messageSize, func(tag Tag, t MsgType) (message, error) {
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c.pendingMu.Lock()
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resp := c.pending[tag]
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c.pendingMu.Unlock()
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// Not expecting this message?
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if resp == nil {
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log.Warningf("client received unexpected tag %v, ignoring", tag)
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return nil, ErrUnexpectedTag
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}
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// Is it an error? We specifically allow this to
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// go through, and then we deserialize below.
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if t == MsgRlerror {
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return &Rlerror{}, nil
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}
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// Does it match expectations?
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if t != resp.r.Type() {
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return nil, &ErrBadResponse{Got: t, Want: resp.r.Type()}
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}
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// Return the response.
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return resp.r, nil
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})
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if err != nil {
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// No tag was extracted (probably a socket error).
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//
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// Likely catastrophic. Notify all waiters and clear pending.
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c.pendingMu.Lock()
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for _, resp := range c.pending {
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resp.done <- err
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}
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c.pending = make(map[Tag]*response)
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c.pendingMu.Unlock()
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} else {
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// Process the tag.
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//
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// We know that is is contained in the map because our lookup function
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// above must have succeeded (found the tag) to return nil err.
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c.pendingMu.Lock()
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resp := c.pending[tag]
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delete(c.pending, tag)
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c.pendingMu.Unlock()
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resp.r = r
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resp.done <- err
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}
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}
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// waitAndRecv co-ordinates with other receivers to handle responses.
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func (c *Client) waitAndRecv(done chan error) error {
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for {
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select {
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case err := <-done:
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return err
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case c.recvr <- true:
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select {
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case err := <-done:
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// It's possible that we got the token, despite
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// done also being available. Check for that.
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<-c.recvr
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return err
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default:
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// Handle receiving one tag.
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c.handleOne()
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// Return the token.
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<-c.recvr
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}
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}
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}
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}
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// sendRecv performs a roundtrip message exchange.
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//
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// This is called by internal functions.
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func (c *Client) sendRecv(t message, r message) error {
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tag, ok := c.tagPool.Get()
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if !ok {
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return ErrOutOfTags
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}
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defer c.tagPool.Put(tag)
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// Indicate we're expecting a response.
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//
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// Note that the tag will be cleared from pending
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// automatically (see handleOne for details).
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resp := responsePool.Get().(*response)
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defer responsePool.Put(resp)
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resp.r = r
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c.pendingMu.Lock()
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c.pending[Tag(tag)] = resp
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c.pendingMu.Unlock()
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// Send the request over the wire.
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c.sendMu.Lock()
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err := send(c.socket, Tag(tag), t)
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c.sendMu.Unlock()
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if err != nil {
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return err
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}
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// Co-ordinate with other receivers.
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if err := c.waitAndRecv(resp.done); err != nil {
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return err
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}
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// Is it an error message?
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//
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// For convenience, we transform these directly
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// into errors. Handlers need not handle this case.
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if rlerr, ok := resp.r.(*Rlerror); ok {
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return syscall.Errno(rlerr.Error)
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}
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// At this point, we know it matches.
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//
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// Per recv call above, we will only allow a type
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// match (and give our r) or an instance of Rlerror.
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return nil
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}
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// Version returns the negotiated 9P2000.L.Google version number.
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func (c *Client) Version() uint32 {
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return c.version
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}
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// Close closes the underlying socket.
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func (c *Client) Close() error {
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return c.socket.Close()
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}
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