Re: [uml-devel] [PATCH] uml: flush stdout before forking

[Richard Weinberger]

On Fri, Dec 18, 2015 at 9:28 PM, Vegard Nossum <vegard.nossum@xxxxxxxxxx> wrote:
> I was seeing some really weird behaviour where piping UML's output
> somewhere would cause output to get duplicated:
>
>   $ ./vmlinux | head -n 40
>   Checking that ptrace can change system call numbers...Core dump limits :
>           soft - 0
>           hard - NONE
>   OK
>   Checking syscall emulation patch for ptrace...Core dump limits :
>           soft - 0
>           hard - NONE
>   OK
>   Checking advanced syscall emulation patch for ptrace...Core dump limits :
>           soft - 0
>           hard - NONE
>   OK
>   Core dump limits :
>           soft - 0
>           hard - NONE
>
> This is because these tests do a fork() which duplicates the non-empty
> stdout buffer, then glibc flushes the duplicated buffer as each child
> exits.
>
> A simple workaround is to flush before forking.
>
> Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>

Applied and queued for stable!

-- 
Thanks,
//richard