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

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Message-ID: <54DB9BD7.7090605@cybernetics.com>
Date:	Wed, 11 Feb 2015 13:13:43 -0500
From:	Tony Battersby <tonyb@...ernetics.com>
To:	dgilbert@...erlog.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 02/11/2015 12:45 PM, Douglas Gilbert wrote:
> 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
>
>
>
I checked before submitting, and the foo ? : bar construct is already
used at least 455 times in the kernel, so it is nothing new.

find linux-3.19 -type f -name "*.[ch]" | xargs grep '\? :' | wc -l
455

But you are probably right; I think that with such small variable names
your version is more readable due to the nesting.  Updated patch below.

---

Fix SCSI generic read() incorrectly returning success after detecting an
error.

Cc: <stable@...r.kernel.org>
Signed-off-by: Tony Battersby <tonyb@...ernetics.com>
---

--- 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	2015-02-11 13:02:56.000000000 -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 ? err : (err2 ? err2 : count);
 }
 
 static ssize_t

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