131 lines
3.2 KiB
Go
131 lines
3.2 KiB
Go
// Copyright 2017 The Periph Authors. All rights reserved.
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// Use of this source code is governed under the Apache License, Version 2.0
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// that can be found in the LICENSE file.
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// Package fs provides access to the file system on the host.
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//
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// It exposes ioctl syscall and epoll in an OS agnostic way and permits
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// completely disabling file access to lock down unit tests.
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package fs
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import (
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"errors"
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"os"
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"sync"
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)
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// Ioctler is a file handle that supports ioctl calls.
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type Ioctler interface {
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// Ioctl sends a linux ioctl on the file handle. op is effectively a uint32.
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//
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// The op is expected to be encoded in the format on x64. ARM happens to
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// share the same format.
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Ioctl(op uint, data uintptr) error
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}
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// Open opens a file.
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//
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// Returns an error if Inhibit() was called.
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func Open(path string, flag int) (*File, error) {
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mu.Lock()
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if inhibited {
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mu.Unlock()
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return nil, errors.New("file I/O is inhibited")
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}
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used = true
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mu.Unlock()
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f, err := os.OpenFile(path, flag, 0600)
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if err != nil {
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return nil, err
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}
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return &File{f}, nil
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}
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// Inhibit inhibits any future file I/O. It panics if any file was opened up to
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// now.
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//
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// It should only be called in unit tests.
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func Inhibit() {
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mu.Lock()
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inhibited = true
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if used {
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panic("calling Inhibit() while files were already opened")
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}
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mu.Unlock()
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}
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// File is a superset of os.File.
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type File struct {
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*os.File
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}
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// Ioctl sends an ioctl to the file handle.
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func (f *File) Ioctl(op uint, data uintptr) error {
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if isMIPS {
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var err error
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if op, err = translateOpMIPS(op); err != nil {
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return err
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}
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}
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return ioctl(f.Fd(), op, data)
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}
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// Event is a file system event.
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type Event struct {
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event
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}
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// MakeEvent initializes an epoll *edge* triggered event on linux.
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//
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// An edge triggered event is basically an "auto-reset" event, where waiting on
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// the edge resets it. A level triggered event requires manual resetting; this
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// could be done via a Read() call but there's no need to require the user to
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// call Read(). This is particularly useless in the case of gpio.RisingEdge and
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// gpio.FallingEdge.
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//
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// As per the official doc, edge triggers is still remembered even when no
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// epoll_wait() call is running, so no edge is missed. Two edges will be
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// coallesced into one if the user mode process can't keep up. There's no
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// accumulation of edges.
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func (e *Event) MakeEvent(fd uintptr) error {
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return e.event.makeEvent(fd)
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}
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// Wait waits for an event or the specified amount of time.
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func (e *Event) Wait(timeoutms int) (int, error) {
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return e.event.wait(timeoutms)
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}
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//
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var (
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mu sync.Mutex
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inhibited bool
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used bool
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)
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func translateOpMIPS(op uint) (uint, error) {
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// Decode the arm/x64 encoding and reencode as MIPS specific linux ioctl.
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// arm/x64: DIR(2), SIZE(14), TYPE(8), NR(8)
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// mips: DIR(3), SIZE(13), TYPE(8), NR(8)
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// Check for size overflow.
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if (op & (1 << (13 + 8 + 8))) != 0 {
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return 0, errors.New("fs: op code size is too large")
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}
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const mask = (1 << (13 + 8 + 8)) - 1
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out := op & mask
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// Convert dir.
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switch op >> (14 + 8 + 8) {
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case 0: // none
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out |= 1 << (13 + 8 + 8)
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case 1: // write
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out |= 4 << (13 + 8 + 8)
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case 2: // read
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out |= 2 << (13 + 8 + 8)
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default:
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return 0, errors.New("fs: op code dir is invalid")
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}
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return out, nil
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}
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