PKGBUILD/vendor/periph.io/x/periph/host/fs/fs.go

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2018-12-04 18:11:50 +00:00
// Copyright 2017 The Periph Authors. All rights reserved.
// Use of this source code is governed under the Apache License, Version 2.0
// that can be found in the LICENSE file.
// Package fs provides access to the file system on the host.
//
// It exposes ioctl syscall and epoll in an OS agnostic way and permits
// completely disabling file access to lock down unit tests.
package fs
import (
"errors"
"os"
"sync"
)
// Ioctler is a file handle that supports ioctl calls.
type Ioctler interface {
// Ioctl sends a linux ioctl on the file handle. op is effectively a uint32.
//
// The op is expected to be encoded in the format on x64. ARM happens to
// share the same format.
Ioctl(op uint, data uintptr) error
}
// Open opens a file.
//
// Returns an error if Inhibit() was called.
func Open(path string, flag int) (*File, error) {
mu.Lock()
if inhibited {
mu.Unlock()
return nil, errors.New("file I/O is inhibited")
}
used = true
mu.Unlock()
f, err := os.OpenFile(path, flag, 0600)
if err != nil {
return nil, err
}
return &File{f}, nil
}
// Inhibit inhibits any future file I/O. It panics if any file was opened up to
// now.
//
// It should only be called in unit tests.
func Inhibit() {
mu.Lock()
inhibited = true
if used {
panic("calling Inhibit() while files were already opened")
}
mu.Unlock()
}
// File is a superset of os.File.
type File struct {
*os.File
}
// Ioctl sends an ioctl to the file handle.
func (f *File) Ioctl(op uint, data uintptr) error {
if isMIPS {
var err error
if op, err = translateOpMIPS(op); err != nil {
return err
}
}
return ioctl(f.Fd(), op, data)
}
// Event is a file system event.
type Event struct {
event
}
// MakeEvent initializes an epoll *edge* triggered event on linux.
//
// An edge triggered event is basically an "auto-reset" event, where waiting on
// the edge resets it. A level triggered event requires manual resetting; this
// could be done via a Read() call but there's no need to require the user to
// call Read(). This is particularly useless in the case of gpio.RisingEdge and
// gpio.FallingEdge.
//
// As per the official doc, edge triggers is still remembered even when no
// epoll_wait() call is running, so no edge is missed. Two edges will be
// coallesced into one if the user mode process can't keep up. There's no
// accumulation of edges.
func (e *Event) MakeEvent(fd uintptr) error {
return e.event.makeEvent(fd)
}
// Wait waits for an event or the specified amount of time.
func (e *Event) Wait(timeoutms int) (int, error) {
return e.event.wait(timeoutms)
}
//
var (
mu sync.Mutex
inhibited bool
used bool
)
func translateOpMIPS(op uint) (uint, error) {
// Decode the arm/x64 encoding and reencode as MIPS specific linux ioctl.
// arm/x64: DIR(2), SIZE(14), TYPE(8), NR(8)
// mips: DIR(3), SIZE(13), TYPE(8), NR(8)
// Check for size overflow.
if (op & (1 << (13 + 8 + 8))) != 0 {
return 0, errors.New("fs: op code size is too large")
}
const mask = (1 << (13 + 8 + 8)) - 1
out := op & mask
// Convert dir.
switch op >> (14 + 8 + 8) {
case 0: // none
out |= 1 << (13 + 8 + 8)
case 1: // write
out |= 4 << (13 + 8 + 8)
case 2: // read
out |= 2 << (13 + 8 + 8)
default:
return 0, errors.New("fs: op code dir is invalid")
}
return out, nil
}