Re: [PATCH] qio: fix command spawn RDONLY/WRONLY

[Daniel P . Berrangé]

On Thu, Sep 01, 2022 at 02:11:20PM +0400, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> The in/out handling is inverted, although nothing seemed to notice that yet.

On the contrary, it is correct, and the unit tests validate this.

> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  io/channel-command.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/io/channel-command.c b/io/channel-command.c
> index 9f2f4a1793..ed17b44f74 100644
> --- a/io/channel-command.c
> +++ b/io/channel-command.c
> @@ -79,10 +79,10 @@ qio_channel_command_new_spawn(const char *const argv[],
>      flags = flags & O_ACCMODE;
>  
>      if (flags == O_RDONLY) {
> -        stdinnull = true;
> +        stdoutnull = true;
>      }
>      if (flags == O_WRONLY) {
> -        stdoutnull = true;
> +        stdinnull = true;
>      }

This change breaks the unit tests.

The confusion is because there are two parties involves. The 'flags'
variable is from the POV of the parent process, while stdinnull/stdoutnull
are from the POV of the child process.

IOW, if the parent process is reading from the child (O_RDONLY),
then the child needs a stdout to write to the parent, but not
any stdin to read from the parent, hence we set stdin to /dev/null
in the child.

With regards,
Daniel
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