linux-kernel - Re: [PATCH] [SCSI] sg: fix read() error reporting

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Date:	Wed, 11 Feb 2015 12:45:32 -0500
From:	Douglas Gilbert <dgilbert@...erlog.com>
To:	Tony Battersby <tonyb@...ernetics.com>, linux-scsi@...r.kernel.org,
	"James E.J. Bottomley" <JBottomley@...allels.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [SCSI] sg: fix read() error reporting

On 15-02-11 11:32 AM, Tony Battersby wrote:
> Fix SCSI generic read() incorrectly returning success after detecting an
> error.
>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Tony Battersby <tonyb@...ernetics.com>
> ---
>
> For inclusion in kernel 3.20.
>
> --- linux-3.19.0/drivers/scsi/sg.c.orig	2015-02-08 21:54:22.000000000 -0500
> +++ linux-3.19.0/drivers/scsi/sg.c	2015-02-10 09:26:09.000000000 -0500
> @@ -546,7 +546,7 @@ static ssize_t
>   sg_new_read(Sg_fd * sfp, char __user *buf, size_t count, Sg_request * srp)
>   {
>   	sg_io_hdr_t *hp = &srp->header;
> -	int err = 0;
> +	int err = 0, err2;
>   	int len;
>
>   	if (count < SZ_SG_IO_HDR) {
> @@ -575,8 +575,8 @@ sg_new_read(Sg_fd * sfp, char __user *bu
>   		goto err_out;
>   	}
>   err_out:
> -	err = sg_finish_rem_req(srp);
> -	return (0 == err) ? count : err;
> +	err2 = sg_finish_rem_req(srp);
> +	return err ? : err2 ? : count;

Tony,
Your point is well made.

I just don't like that last line, using a gcc extension that
hasn't even made it into C11 (or C++11). Wouldn't:
     return err ? err : (err2 ? err2 : count);

be a bit better? I think the following snippet makes the intent
clear but would it generate any more code:
     if (err || err2)
	return err ? err : err2;
     else
         return count;

Doug Gilbert


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