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-rw-r--r--inotify/inotify.go250
1 files changed, 188 insertions, 62 deletions
diff --git a/inotify/inotify.go b/inotify/inotify.go
index 2fd3a83..2db414c 100644
--- a/inotify/inotify.go
+++ b/inotify/inotify.go
@@ -1,4 +1,4 @@
-// Copyright 2015 Luke Shumaker <lukeshu@sbcglobal.net>.
+// Copyright 2015-2016 Luke Shumaker <lukeshu@sbcglobal.net>.
//
// This is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as
@@ -22,16 +22,54 @@ import (
"sync"
"syscall"
"unsafe"
+ "os"
)
+// Most of the complexity here is that we syncronize around access to
+// the file descriptor. Why? Because we're worried that it could get
+// closed and re-used between the time the fd is read from the os.File
+// and the time the system call is actually dispatched.
+//
+// A B
+// in.method() in.Close(); syscall.Open()
+// ---------------------------------------------------
+// fd = in.fd
+// syscall.Close()
+// syscall.Open()
+// syscall(fd)
+//
+// And you're wondering "should we really protoect against that; after
+// all: share by communicating, don't communicate by sharing" and "why
+// do we have to deal with this condition if os.File doesn't?"
+// Because an inotify instance is more like a net.Listener. If you
+// notice, net.netFD has do deal with a very similar situtation. At
+// some level, you may simply observe that with inotify it makes sense
+// to have one goroutine add/remove watches, and have another read
+// them; where this kind of communication doesn't make sense with
+// ordinary files.
+//
+// So, how does net.netFD deal with it? Well... it is tightly coupled
+// with some private routines in runtime/sema.go. That is, we can't
+// look at it for too much guidance.
+
type Inotify struct {
- fd file
- fdLock sync.RWMutex
- buffFull [4096]byte
+ fd inFd
+ fdLock sync.RWMutex
+ fdBlock bool
+
+ buffFull [4096]byte // 4KiB is a good size, but the bare
+ // minimum is `sizeof(struct
+ // inotify_event) + NAME_MAX + 1`
buff []byte
buffLock sync.Mutex
+ buffErr error
+
+ ch chan chev
}
+// Event is a file system event from inotify.
+//
+// An Event is invalid if Wd is < 0.
type Event struct {
Wd Wd // Watch descriptor
Mask Mask // Mask describing event
@@ -39,90 +77,178 @@ type Event struct {
Name *string // Optional name
}
-// Create an inotify instance. The variant InotifyInit1() allows
-// flags to access extra functionality.
-func InotifyInit() (*Inotify, error) {
- fd, err := inotify_init()
- o := Inotify{
+type chev struct {
+ Ev Event
+ Err error
+}
+
+func newInotify(fd inFd, blocking bool) *Inotify {
+ if fd < 0 {
+ return nil
+ }
+ in := &Inotify{
fd: fd,
+ fdBlock: blocking,
+ ch: make(chan chev),
}
- o.buff = o.buffFull[:0]
- return &o, err
+ in.buff = in.buffFull[:0]
+ go in.worker()
+ return in
}
-// Create an inotify instance, with flags specifying extra
-// functionality.
+// InotifyInit creates an inotify instance. The variant
+// InotifyInit1() allows flags to access extra functionality.
+func InotifyInit() (*Inotify, error) {
+ fd, err := sys_inotify_init()
+ return newInotify(fd, true), err
+}
+
+// InotifyInit1 create an inotify instance, with flags specifying
+// extra functionality.
func InotifyInit1(flags int) (*Inotify, error) {
- fd, err := inotify_init1(flags)
- o := Inotify{
- fd: fd,
- }
- o.buff = o.buffFull[:0]
- return &o, err
+ fd, err := sys_inotify_init1(flags &^ IN_NONBLOCK)
+ return newInotify(fd, flags & IN_NONBLOCK == 0), err
}
-// Add a watch to the inotify instance, or modifies an existing watch
-// item.
-func (o *Inotify) AddWatch(path string, mask Mask) (Wd, error) {
- o.fdLock.RLock()
- defer o.fdLock.RUnlock()
- return inotify_add_watch(o.fd, path, mask)
+// AddWatch adds a watch to the inotify instance, or modifies an
+// existing watch item.
+func (in *Inotify) AddWatch(path string, mask Mask) (Wd, error) {
+ in.fdLock.RLock()
+ defer in.fdLock.RUnlock()
+ return sys_inotify_add_watch(in.fd, path, mask)
}
-// Remove a watch from the inotify instance.
-func (o *Inotify) RmWatch(wd Wd) error {
- o.fdLock.RLock()
- defer o.fdLock.RUnlock()
- return inotify_rm_watch(o.fd, wd)
+// RmWatch removes a watch from the inotify instance.
+func (in *Inotify) RmWatch(wd Wd) error {
+ in.fdLock.RLock()
+ defer in.fdLock.RUnlock()
+ return sys_inotify_rm_watch(in.fd, wd)
}
-// Close the inotify instance; further calls to this object will
-// error.
-//
-// Events recieved before Close() is called may still be Read() after
-// the call to Close().
-//
-// Beware that if Close() is called while waiting on Read(), it will
-// block until events are read.
-func (o *Inotify) Close() error {
- o.fdLock.Lock()
- defer o.fdLock.Unlock()
- defer func() { o.fd = -1 }()
- return sysclose(o.fd)
+// Close closes the inotify instance; further calls to this object
+// will error.
+func (in *Inotify) Close() (err error) {
+ defer func() {
+ if r := recover(); r != nil {
+ // This is a double-close condition.
+ //
+ // Choices for the error:
+ // - Linux: EBADF
+ // - os.File: syscall.EINVAL
+ // - net.netFD: net.errClosing = errors.New(...)
+ err = os.NewSyscallError("close", syscall.EBADF)
+ }
+ }()
+ close(in.ch) // will panic if already closed; hence above
+
+ // I would love to be able to return the error from sys_close;
+ // but it might block forever.
+ go func() {
+ in.fdLock.Lock()
+ in.fdLock.Unlock()
+ sys_close(in.fd)
+ }()
+ return
}
-// Read an event from the inotify instance.
+// read is a low-level read an event from the inotify instance.
//
-// Events recieved before Close() is called may still be Read() after
-// the call to Close().
-func (o *Inotify) Read() (Event, error) {
- o.buffLock.Lock()
- defer o.buffLock.Unlock()
-
- if len(o.buff) == 0 {
- o.fdLock.RLock()
- len, err := sysread(o.fd, o.buffFull[:])
- o.fdLock.RUnlock()
- if len == 0 {
- return Event{Wd: -1}, o.Close()
- } else if len < 0 {
- return Event{Wd: -1}, err
+// It's low-level/private because it can deadlock between it and the
+// `go` block in Close. Instead, a worker calls this in a loop,
+// writes the result to a channel, and a public reader can safely get
+// it from the channel. No deadlock.
+func (in *Inotify) read() (Event, error) {
+ in.buffLock.Lock()
+ defer in.buffLock.Unlock()
+
+ if len(in.buff) == 0 {
+ if in.buffErr != nil {
+ return Event{Wd: -1}, in.buffErr
}
- o.buff = o.buffFull[0:len]
+ var n int
+ in.fdLock.RLock()
+ n, in.buffErr = sys_read(in.fd, in.buffFull[:])
+ in.fdLock.RUnlock()
+ in.buff = in.buffFull[0:n]
}
- raw := (*syscall.InotifyEvent)(unsafe.Pointer(&o.buff[0]))
+ if len(in.buff) < syscall.SizeofInotifyEvent {
+ // Either Linux screwed up (and we have no chance of
+ // handling that sanely), or this Inotify came from an
+ // existing FD that wasn't really an inotify instance.
+ in.buffErr = syscall.EBADF
+ return Event{Wd: -1}, in.buffErr
+ }
+ raw := (*syscall.InotifyEvent)(unsafe.Pointer(&in.buff[0]))
ret := Event{
Wd: Wd(raw.Wd),
Mask: Mask(raw.Mask),
Cookie: raw.Cookie,
Name: nil,
}
+ if int64(len(in.buff)) < syscall.SizeofInotifyEvent+int64(raw.Len) {
+ // Same as above.
+ in.buffErr = syscall.EBADF
+ return Event{Wd: -1}, in.buffErr
+ }
if raw.Len > 0 {
- bytes := (*[syscall.NAME_MAX]byte)(unsafe.Pointer(&o.buff[syscall.SizeofInotifyEvent]))
+ bytes := (*[syscall.NAME_MAX]byte)(unsafe.Pointer(&in.buff[syscall.SizeofInotifyEvent]))
name := string(bytes[:raw.Len-1])
ret.Name = &name
}
- o.buff = o.buff[0 : syscall.SizeofInotifyEvent+raw.Len]
+ in.buff = in.buff[0 : syscall.SizeofInotifyEvent+raw.Len]
return ret, nil
}
+
+func (in *Inotify) worker() {
+ defer recover()
+ for {
+ ev, err := in.read()
+ in.ch <- chev{ev, err} // will panic on .Close()
+ }
+}
+
+// Read calls either ReadBlock or ReadNonblock, depending on whether
+// the Inotify instance has the IN_NONBLOCK flag set.
+func (in *Inotify) Read() (Event, error) {
+ if in.fdBlock {
+ return in.ReadBlock()
+ } else {
+ return in.ReadNonblock()
+ }
+}
+
+// ReadBlock reads exactly one Event or an error from the inotify
+// instance. If an Event or error is not available for reading, it
+// blocks until one is.
+//
+// If err is non-nil, then the Event is invalid (ev.Wd < 0); and if
+// err is nil, then then the Event is valid.
+func (in *Inotify) ReadBlock() (Event, error) {
+ e, ok := <-in.ch
+ if !ok {
+ return Event{Wd: -1}, os.NewSyscallError("read", syscall.EBADF)
+ }
+ return e.Ev, e.Err
+}
+
+// ReadNonblock reads either an Event or an error from the inotify
+// instance, but doesn't block if an event isn't ready.
+//
+// Unlike Read, it may be the case that both the Event is invalid and
+// the error is nil. This indicates that the read simply returned
+// instead of blocking.
+//
+// ev, err := in.ReadNonblock()
+// haveRead = ev.Wd >= 0 || err != nil
+func (in *Inotify) ReadNonblock() (Event, error) {
+ select {
+ case e, ok := <-in.ch:
+ if !ok {
+ return Event{Wd: -1}, os.NewSyscallError("read", syscall.EBADF)
+ }
+ return e.Ev, e.Err
+ default:
+ return Event{Wd: -1}, nil
+ }
+}
generated by cgit v1.1-4-g5e80 at 2024-04-26 18:43:06 +0000