[Ocfs2-test-devel] [PATCH 42/59] mmap-test: fix segment fault

[Junxiao Bi]

On 09/23/2015 01:13 PM, Eric Ren wrote:
> Hello Junxiao,
> 
> Please look at comment below.
> 
> On Mon, Sep 14, 2015 at 10:44:28AM +0800, Junxiao Bi wrote: 
>> When test file size is multiple of page size, there will be write out of
>> mmap range and cause segment fault.
>>
>> Signed-off-by: Junxiao Bi <junxiao.bi at oracle.com>
>> ---
>>  programs/mmap_test/mmap_test.c |    8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/programs/mmap_test/mmap_test.c b/programs/mmap_test/mmap_test.c
>> index 9edbb58..711bb81 100644
>> --- a/programs/mmap_test/mmap_test.c
>> +++ b/programs/mmap_test/mmap_test.c
>> @@ -80,6 +80,14 @@ int main(int argc, char *argv[])
>>      }
>>  
>>      offset = stat_buf.st_size % page_size;
>> +
>> +    /* fix offset if the file size is multiple of page size */
>> +    if (offset == 0)
>> +	    offset = page_size;
>> +
> 
> I cannot understand the below.
> 1. if (.st_size < page_size && .st_size != 0)
>         both if-statement won't hit;
> 
> 2. if (.st_size > page_size && .st_size % page_size != 0)
>         1st if-statement won't hit;
>         2st if-statement won't hit, also;
> 
> 3. if (.st_size !=0 && .st_size % page_size == 0)
>         1st if-statement hit!
>         2st if-statement won't hit!
> 
> 4. if (.st_size == 0)
>         1st if-statement hit;
>         2st if-statement will hit!!! As a result, offset varied 0,
>         page_size, and 0 again.
> 
> So, the 2th if-statement is odd! Or I mistake something?
2th is for the case st_size == 0, do you mean it's useless and can be
dropped?

Thanks,
Junxiao.
> 
> Thanks,
> Eric Ren
> 
>> +    if (offset > stat_buf.st_size)
>> +	    offset = stat_buf.st_size;
>> +
>>      ptr = buf + (stat_buf.st_size - offset);
>>      remain = page_size - offset;
>>  
>> -- 
>> 1.7.9.5
>>
>>
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