linux-kernel - Re: [V2, 06/12] selftests, powerpc: Add test for system wide DSCR default

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Date:	Thu, 09 Apr 2015 16:01:03 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	Michael Ellerman <mpe@...erman.id.au>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
CC:	mikey@...ling.org, anton@...ba.org
Subject: Re: [V2, 06/12] selftests, powerpc: Add test for system wide DSCR
 default

On 03/27/2015 05:31 PM, Michael Ellerman wrote:
> On Tue, 2015-13-01 at 10:22:34 UTC, Anshuman Khandual wrote:
>> This patch adds a test case for the system wide DSCR default
>> value, which when changed through it's sysfs interface must
>> be visible to all threads reading DSCR either through the
>> privilege state SPR or the problem state SPR. The DSCR value
>> change should be immediate as well.
> 
> ...
> 
>> +
>> +/* Default DSCR access */
>> +unsigned long get_default_dscr(void)
>> +{
>> +	int fd = -1;
>> +	char buf[16];
>> +	unsigned long val;
>> +
>> +	if (fd == -1) {
>> +		fd = open(DSCR_DEFAULT, O_RDONLY);
>> +		if (fd == -1) {
>> +			perror("open() failed\n");
>> +			exit(1);
>> +		}
>> +	}
>> +	memset(buf, 0, sizeof(buf));
>> +	lseek(fd, 0, SEEK_SET);
>> +	read(fd, buf, sizeof(buf));
> 

Normally, I build the test cases like

$cd tools/testing/selftests/powerpc/
$make dscr

with these compiler flags "-Wall -O2 -flto -Wall -Werror" which
is still working for me. Then I figured out that the read and
write declaration in unistd.h header file has "_wur" in it.

extern ssize_t read (int __fd, void *__buf, size_t __nbytes) __wur;
extern ssize_t write (int __fd, const void *__buf, size_t __n) __wur;

Then some how the compiler (GCC 4.8.3) is not complaining about it.

> 
> This and the other tests are failing to build:
> 
>     In file included from dscr_default_test.c:16:0:
>     dscr.h: In function â€˜get_default_dscrâ€™:
>     dscr.h:93:6: error: ignoring return value of â€˜readâ€™, declared with attribute warn_unused_result [-Werror=unused-result]
>       read(fd, buf, sizeof(buf));
>           ^
>     dscr.h: In function â€˜set_default_dscrâ€™:
>     dscr.h:112:7: error: ignoring return value of â€˜writeâ€™, declared with attribute warn_unused_result [-Werror=unused-result]
>       write(fd, buf, strlen(buf));
>            ^
>     cc1: all warnings being treated as errors

Anyways, I can change the header file helper functions if you would like.
BTW, the patch series does not apply as it is and requires rebasing. Would
send out a new version of it.

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