[PATCH V3 00/11] telemetry: add u32 value type and hex integer string API

[lihuisong (C)]

在 2022/12/12 20:03, Morten Brørup 写道:
>> From: Bruce Richardson [mailto:bruce.richardson at intel.com]
>> Sent: Monday, 12 December 2022 12.21
>>
>> On Mon, Dec 12, 2022 at 12:02:32PM +0100, Morten Brørup wrote:
>>>> From: Bruce Richardson [mailto:bruce.richardson at intel.com]
>>>> Sent: Monday, 12 December 2022 11.32
>>>>
>>>> On Mon, Dec 12, 2022 at 02:42:55PM +0800, Huisong Li wrote:
>>>>> Some lib telemetry interfaces add the 'u32' and 'u64' data by the
>>>>> rte_tel_data_add_dict/array_int API. This may cause data
>> conversion
>>>> error
>>>>> or data truncation.
>>>>>
>>>>> The 'u32' data can not be assigned to signed 32-bit integer.
>> However,
>>>>> assigning to u64 is very wasteful, after all, the buffer capacity
>> of
>>>> each
>>>>> transfer is limited. So it is necessary for 'u32' data to add
>> usigned
>>>>> 32-bit integer type and a series of 'u32' operation APIs.
>>>>>
>>>>> This patchset uses the new 'u32' API to resolve the problem of
>> data
>>>>> conversion error, and use the 'u64' API to add 'u64' data.
>>>>>
>>>>> In addition, this patchset introduces two APIs to store u32 and
>> u64
>>>>> values as hexadecimal encoded strings in telemetry library.
>>>>>
>>>>> --- -v3: fix a misspelling mistake in commit log.  -v2: - fix ABI
>>>> break
>>>>> warning.  - introduce two APIs to store u32 and u64 values as
>>>> hexadecimal
>>>>> encoded strings.
>>>>>
>>>> I'm not convinced about adding the u32 value generically to the
>>>> telemetry
>>>> lib - except in the case of having explicit function calls for u32
>> vs
>>>> u64
>>>> hex strings. Having a u32 type doesn't gain us any space internally
>>>> over a
>>>> u64 value, since all values are in a union type. Also, for output
>> as
>>>> json,
>>>> the numeric values are all output as decimal values, meaning that
>> the
>>>> value
>>>> 1 appears as the same size in the output string whether it is a u32
>> or
>>>> u64
>>>> type. Now, it may save space in a future binary output format, but
>> even
>>>> then it still may not do so.
>>> I agree that a u32 doesn't gain any space internally.
>>>
>>> However, many SNMP counters are unsigned 32 bit, and expected to wrap
>> around as such.
>>> So I suppose the u32 type might be useful for SNMP, if obtained
>> through the telemetry library.
>>> Alternatively, we could somehow reuse the u64 type and require the
>> application to pass (value & UINT32_MAX) to the u64 functions. To make
>> this easy to use, we should add some wrappers to do it for the
>> application. And eventually we would probably end up with something
>> very similar to this patch.
>> I think just using the u64 functions is probably simplest and best
>> right
>> now. If we add support for something like snmp then yes, it would make
>> sense to explicitly add it, but it seems like a lot of extra code for
>> little or no benefit until we support something like that.
> <rant>
> If we wanted to fix this generally, we should rely on type promotion, so the existing _int function should be updated to take an int64_t value, and the _u64 function should be renamed to _uint (and still take an uint64_t value). However, that would break the ABI, and would need to go through some process for that. So let's not change this now.
> </rant>
>
> I tend to agree with Bruce on this: Let's get rid of the new u32 functions, and rely on the u64 functions for that instead.
All right. Let's drop the new u32 functions.
>
>>>> Therefore, I'd tend to keep the existing u64 type as-is, and
>> instead
>>>> only
>>>> add the functions for outputting hex values. Those hex output
>> functions
>>>> could take an additional parameter indicating the desired hex
>> output
>>>> length, as there could well be cases where we want just 16-bit hex
>>>> value
>>>> too.
>>> The way I read the patch series, the hex output length is not fixed,
>> but an u64 value of 5 will be output as 0x5, not 0x0000000000000005.
>>> So the only benefit of having both u32_hex and u64_hex functions is
>> to avoid type promotion from uint32_t to uint64_t on input for 32 bit
>> values.
>>> Instead of passing a 3rd parameter or adding u16_hex functions, we
>> could consider just having one set of hex functions using uint64_t for
>> the value, and rely on type promotion for 32 and 16 bit values.
>> +1 to having only a single hex function, and I think type promotion
>> should
>> work fine.
>>
>> However, I still think it might be worthwhile allowing the user to pass
>> in
>> a min output length parameter too. I find for many hex strings having
>> the
>> leading zeros to explicitly show the length can be useful. The value
>> "0"
>> could cover the current behaviour of no-padding, otherwise the
>> parameter
>> should indicate the number of bits to be displayed. (If we want to lock
>> it
>> down we can use an enum parameter rather than int to limit it to 0, 8,
>> 16,
>> 32 or 64 bit displayed values).
> An extra parameter for minimum output length (in number of input bits) would be very nice, and makes avoids a set of functions for each bit width.
>
> (I don't think it should be lock it down to some special bit lengths; there is no need to prevent 24 bit or other exotic bit widths.)
>
> Something like this:
>
> char str[64]; // Big enough length.
> if (bits != 0) {
>    char format[16]; // Big enough length.
>    sprintf(format, "0x0%u%" PRIx64, (bits + 3) / 4);
>    sprintf(str, format, value);
> } else {
>    sprintf(str, "0x%" PRIx64, value);
> }
Fix it in v4.
>> All that said, I'm not massively concerned if we want to just keep the
>> current approach of always just printing without any leading zeros.
>> It's a
>> nice-to-have only for me.
>>
>> /Bruce
>
> .