Re: [PATCH] t9010: Open backflow FIFO once to work around kernel race condition

From: Stefano Lattarini <stefano.lattarini@gmail.com>
Date: Jun 26, 2012, 23:08 UTC
Message-ID: <4FEA40FC.2080604@gmail.com>
In-Reply-To: <20120626224053.GA7155@burratino>

[Adding bug-autoconf]

On 06/27/2012 12:40 AM, Jonathan Nieder wrote:

Show 11 quoted lines

> Hi,
> 
> Quick first impressions:
> 
> Anders Kaseorg wrote:
> 
>> Sidestep this problem by opening the backflow FIFO once for
>> read+write.
> 
> Is that portable?
>

According to the Autoconf manual, no:

    Some shells, like ash, don't recognize bi-directional redirection (‘<>’).
    And even on shells that recognize it, it is not portable to use on fifos:
    Posix does not require read-write support for named pipes, and Cygwin
    does not support it:

       $ mkfifo fifo
       $ exec 5<>fifo
       $ echo hi >&5
       bash: echo: write error: Communication error on send

But while the issue about Cygwin might still be relevant, the one about ash seems to be out-of-date: I've verified that the "exec 5<>fifo" command works with both dash 0.5.2 and dash 0.5.5.1 (that's why I'm CC:ing bug-autoconf).

Regards,
  Stefano