Re: [PATCH v3 02/25] printk: Add print format (%par) for struct range

Andy Shevchenko
2024-08-27T13:18:09Z

On Mon, Aug 26, 2024 at 04:17:52PM -0500, Ira Weiny wrote:
> Andy Shevchenko wrote:
> > On Mon, Aug 26, 2024 at 03:23:50PM +0200, Petr Mladek wrote:
> > > On Thu 2024-08-22 21:10:25, Andy Shevchenko wrote:
> > > > On Thu, Aug 22, 2024 at 12:53:32PM -0500, Ira Weiny wrote:
> > > > > Petr Mladek wrote:
> > > > > > On Fri 2024-08-16 09:44:10, Ira Weiny wrote:

...

> > > > > > > + %par [range 0x60000000-0x6fffffff] or
> > > > > >
> > > > > > It seems that it is always 64-bit. It prints:
> > > > > >
> > > > > > struct range {
> > > > > > u64 start;
> > > > > > u64 end;
> > > > > > };
> > > > >
> > > > > Indeed. Thanks I should not have just copied/pasted.
> > > >
> > > > With that said, I'm not sure the %pa is a good placeholder for this ('a' stands
> > > > to "address" AFAIU). Perhaps this should go somewhere under %pr/%pR?
>
> I'm speaking a bit for Dan here but also the logical way I thought of
> things.
>
> 1) %p does not dictate anything about the format of the data. Rather
> indicates that what is passed is a pointer. Because we are passing a
> pointer to a range struct %pXX makes sense.

There is no objection to that.

> 2) %pa indicates what follows is 'address'. This was a bit of creative
> license because, as I said in the commit message most of the time
> struct range contains an address range. So for this narrow use case it
> also makes sense.

As in the discussion it was pointed out that struct range is always 64-bit,
limiting it to the "address" is a wrong assumption as we are talking generic
printing routine here. We don't know what users will be in the future on 32-bit
platforms, or what data (semantically) is being held by this structure.

> 3) %par r for range.

I understand, but again struct range != address.

> %p[rR] is taken.
> %pra confuses things IMO.

It doesn't confuse me. :-) But I believe Petr also has a rationale behind this
proposal as he described earlier.

> > > The r/R in %pr/%pR actually stands for "resource".
> > >
> > > But "%ra" really looks like a better choice than "%par". Both
> > > "resource" and "range" starts with 'r'. Also the struct resource
> > > is printed as a range of values.
>
> %r could be used I think. But this breaks with the convention of passing a
> pointer and how to interpret it. The other idea I had, mentioned in the commit
> message was %pn. Meaning passed by pointer 'raNge'.

No, we can't use %r or anything else that is documented for the standard
printf() format specifiers, otherwise you will get a compiler warning and
basically it means no go.

> I think that follows better than %r. That would be another break from C99.
> But we don't have to follow that.
>
> > Fine with me as long as it:
> > 1) doesn't collide with %pa namespace
> > 2) tries to deduplicate existing code as much as possible.
>
> Andy, I'm not quite following how you expect to share the code between
> resource_string() and range_string()?
>
> There is very little duplicated code. In fact with Petr's suggestions and some
> more work range_string() is quite simple:
>
> +static noinline_for_stack
> +char *range_string(char *buf, char *end, const struct range *range,
> + struct printf_spec spec, const char *fmt)
> +{
> +#define RANGE_DECODED_BUF_SIZE ((2 * sizeof(struct range)) + 4)
> +#define RANGE_PRINT_BUF_SIZE sizeof("[range -]")
> + char sym[RANGE_DECODED_BUF_SIZE + RANGE_PRINT_BUF_SIZE];
> + char *p = sym, *pend = sym + sizeof(sym);

Missing check for pointer, but it's not that I wanted to tell.

> + *p++ = '[';
> + p = string_nocheck(p, pend, "range ", default_str_spec);

Hmm... %pr uses str_spec, what the difference can be here?

> + p = special_hex_number(p, pend, range->start, sizeof(range->start));
> + *p++ = '-';
> + p = special_hex_number(p, pend, range->end, sizeof(range->end));

This is basically the copy of %pr implementation.

p = number(p, pend, res->start, *specp);
if (res->start != res->end) {
*p++ = '-';
p = number(p, pend, res->end, *specp);
}

Would it be possible to unify? I think so, but it requires a bit of thinking.

That's why testing is very important in this kind of generic code.

> + *p++ = ']';
> + *p = '\0';
> +
> + return string_nocheck(buf, end, sym, spec);
> +}
>
> Also this is the bulk of the patch except for documentation and the new
> testing code. [new patch below]
>
> Am I missing your point somehow?

See above.

> I considered cramming a struct range into a
> struct resource to let resource_string() process the data. But that would
> involve creating a new IORESOURCE_* flag (not ideal) and also does not allow
> for the larger u64 data in struct range should this be a 32 bit physical
> address config.

No, that's not what I was expecting.

> Most importantly that would not be much less code AFAICT.

...

> + %par [range 0x0000000060000000-0x000000006fffffff]

I still think this is not okay to use %pa namespace.

...

> +static void __init
> +struct_range(void)
> +{
> + struct range test_range = {
> + .start = 0xc0ffee00ba5eba11,
> + .end = 0xc0ffee00ba5eba11,
> + };
> +
> + test("[range 0xc0ffee00ba5eba11-0xc0ffee00ba5eba11]",
> + "%par", &test_range);
> +
> + test_range = (struct range) {
> + .start = 0xc0ffee,
> + .end = 0xba5eba11,
> + };
> + test("[range 0x0000000000c0ffee-0x00000000ba5eba11]",
> + "%par", &test_range);

Case when start == end?
Case when end < start?

> +}

...

> + *p++ = '[';
> + p = string_nocheck(p, pend, "range ", default_str_spec);
> + p = special_hex_number(p, pend, range->start, sizeof(range->start));
> + *p++ = '-';
> + p = special_hex_number(p, pend, range->end, sizeof(range->end));
> + *p++ = ']';
> + *p = '\0';

As per above comments.

--
With Best Regards,
Andy Shevchenko