linux-kernel - Re: [PATCH 2/4] um: os_set_fd_block: Return old blocking mode

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Date:   Tue, 04 Jan 2022 10:00:25 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Richard Weinberger <richard@....at>, linux-um@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, anton.ivanov@...bridgegreys.com
Subject: Re: [PATCH 2/4] um: os_set_fd_block: Return old blocking mode

On Sat, 2022-01-01 at 22:58 +0100, Richard Weinberger wrote:
> This will be needed when we restore the old mode upon exit.
> The function now returns < 0 in case of an error, 1 if O_NONBLOCK
> was set, 0 otherwise.
> 
> +++ b/arch/um/drivers/chan_user.c
> @@ -257,7 +257,7 @@ static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
>  	}
>  
>  	err = os_set_fd_block(*fd_out, 0);
> -	if (err) {
> +	if (err < 0) {
>  		printk(UM_KERN_ERR "winch_tramp: failed to set thread_fd "
>  		       "non-blocking.\n");
>  		goto out_close;

This does 'return err' afterwards, which then changes the logic from 0
to 1, which seems wrong - especially given that it gets passed further
elsewhere as a pid, which seems very questionable in the first place,
but at least 1 would be valid pid unlike 0?

IOW, I think you need

-	return err;
+	return 0;

a couple of lines later.

johannes