Re: [Xen-devel] [PATCH] x86: fix off-by-one error when printing memory ranges

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.02.2020 12:34, Wei Liu wrote:
> On Wed, Feb 05, 2020 at 11:45:39AM +0000, Wei Liu wrote:
>> On Wed, Feb 05, 2020 at 09:12:50AM +0100, Jan Beulich wrote:
>>> On 04.02.2020 18:19, Wei Liu wrote:
>>>> On Tue, Feb 04, 2020 at 06:07:00PM +0100, Jan Beulich wrote:
>>>>> On 04.02.2020 17:55, Wei Liu wrote:
>>>>>> Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
>>>>>> ---
>>>>>>  xen/arch/x86/e820.c | 2 +-
>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/xen/arch/x86/e820.c b/xen/arch/x86/e820.c
>>>>>> index b9f589cac3..d67387f137 100644
>>>>>> --- a/xen/arch/x86/e820.c
>>>>>> +++ b/xen/arch/x86/e820.c
>>>>>> @@ -94,7 +94,7 @@ static void __init print_e820_memory_map(struct 
>>>>>> e820entry *map, unsigned int ent
>>>>>>      for (i = 0; i < entries; i++) {
>>>>>>          printk(" %016Lx - %016Lx ",
>>>>>>                 (unsigned long long)(map[i].addr),
>>>>>> -               (unsigned long long)(map[i].addr + map[i].size));
>>>>>> +               (unsigned long long)(map[i].addr + map[i].size) - 1);
>>>>>
>>>>> Why was this an error? If we used [,] like Linux does - sure.
>>>>> But we don't. The presentation, without looking at the source,
>>>>> simply leaves open whether this was meant to be [,] or [,).
>>>>> And it continues to be left open with the adjustment made.
>>>>>
>>>>
>>>> Well, Linux's representation is not what is normally done in math
>>>> either.
>>>>
>>>> It is like
>>>>
>>>>   Xen: [mem 0x0000000000000000-0x000000000009efff] usable
>>>>
>>>> Note it is using '-', not ','. And there is "mem" at the beginning.
>>>>
>>>> I have always interpreted the [] pair as something to enclose the range,
>>>> not of mathematically meaning.
>>>>
>>>> If you want, I can change Xen's format string to "[%016Lx, %016Lx]".
>>>
>>> I think this would make things less ambiguous, yes. But my primary
>>> request here is to have neither "fix" nor "error" nor anything
>>> alike in the title or description.
>>
>> OK. I can certainly change the subject line to
>>
>>   x86: subtract 1 when printing e820 ranges
> 
> If I hear no further objections I will commit this patch with the above
> subject line today.

And with the presentation changed to [,]?

Jan

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