Change file descriptor to be blocking. #4
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tqorange
reviewed
Feb 2, 2019
| @@ -41,6 +41,7 @@ func getRawFtraceChan(fp FileProvider, cpu int, doneCh <-chan bool) (<-chan []by | |||
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| for { | |||
| var buf = make([]byte, syscall.Getpagesize()) | |||
| syscall.SetNonblock(int(f.(*os.File).Fd()), false) | |||
tqorange
approved these changes
Feb 2, 2019
Setheck
reviewed
Feb 2, 2019
| @@ -41,6 +41,7 @@ func getRawFtraceChan(fp FileProvider, cpu int, doneCh <-chan bool) (<-chan []by | |||
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| for { | |||
| var buf = make([]byte, syscall.Getpagesize()) | |||
| syscall.SetNonblock(int(f.(*os.File).Fd()), false) | |||
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Is this all we need? I thought I tried this out. Then Reading
golang/go#22939 and https://go-review.googlesource.com/c/go/+/100077/13
I was under the impression we needed to change the os.Open in file.go to something closer to os.NewFile then make the call to syscall.SetNonblock (golang/go#22939 (comment))
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I tried replacing Open with OpenFile, passing in O_NONBLOCK. I also tried setting `syscall.SetNonblock(fd, false)` immediately after the OpenFile and earlier in the loop.
I think the go runtime is adjusting the state of the file descriptor. For example (https://golang.org/src/os/file_unix.go <https://golang.org/src/os/file_unix.go>) changes it when you call Fd(), why not in other places?
It is by making the Read() call /blocking/ that our previous behavior is preserved, as we’ve always been working with blocking files (pipes) and the Select() call to switch between them.
But I admit I’m fairly perplexed by it as well.
… On Feb 1, 2019, at 5:33 PM, Seth ***@***.***> wrote:
@Setheck commented on this pull request.
In ftrace/raw.go <#4 (comment)>:
> @@ -41,6 +41,7 @@ func getRawFtraceChan(fp FileProvider, cpu int, doneCh <-chan bool) (<-chan []by
for {
var buf = make([]byte, syscall.Getpagesize())
+ syscall.SetNonblock(int(f.(*os.File).Fd()), false)
Is this all we need? I thought I tried this out. Then Reading
golang/go#22939 <golang/go#22939> and https://go-review.googlesource.com/c/go/+/100077/13 <https://go-review.googlesource.com/c/go/+/100077/13>
I was under the impression we needed to change the os.Open in file.go to something closer to os.NewFile then make the call to syscall.SetNonblock (golang/go#22939 (comment) <golang/go#22939 (comment)>)
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nkirsch
changed the title
…d pipes as non-blocking - and we ultimately want to force blocking behavior.
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This appears to be changed via the go runtime, as we need to set the file descriptor type prior to each read call.
gatherseems to function the same in go1.8 or go 1.11.