On Thu, Dec 28, 2017 at 2:31 PM, Viacheslav Biriukov
<v.v.biriu...@gmail.com> wrote:
>
> Could you please help me with the following code with O_DIRECT and array. I
> tried to implement direct io and stuck with weird behaviour of alignment
> writes created from array.
>
>
> Following code doesn't work:
>
>
> package main
>
>
> import (
>
> "os"
>
> "syscall"
>
> )
>
>
> func main() {
>
> var p [2 << 16]byte
>
> for i := 0; i < len(p); i++ {
>
> p[i] = byte(' ' + i%('~'-' '))
>
> }
>
>
> f, _ := os.OpenFile("/tmp/1.txt",
> os.O_TRUNC|os.O_CREATE|os.O_WRONLY|syscall.O_DIRECT, 0666)
>
> defer f.Close()
>
>
> f.Write(p[:])
>
> }
>
>
> But, if I make a copy of that array – it's OK:
>
>
> package main
>
>
> import (
>
> "os"
>
> "syscall"
>
> )
>
>
> func main() {
>
> var p [2 << 16]byte
>
> for i := 0; i < len(p); i++ {
>
> p[i] = byte(' ' + i%('~'-' '))
>
> }
>
>
> f, _ := os.OpenFile("/tmp/1.txt",
> os.O_TRUNC|os.O_CREATE|os.O_WRONLY|syscall.O_DIRECT, 0666)
>
> defer f.Close()
>
>
> var a []byte // <----- copy
>
> a = append(a, p[:]...) // <----/
>
> f.Write(a)
>
> }
>
>
> Can't figure this out. And how to catch such behaviour in runtime.
1) Always check your errors. You are ignoring the error return of
os.OpenFile and f.Write and f.Close.
2) You asked for help but all you said was that your code "doesn't
work." Tell us what you expected, and precisely what happened
instead.
Ian
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