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

Ira Weiny
2024-08-27T21:45:21Z

Petr Mladek wrote:
> On Mon 2024-08-26 16:17:52, 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.
> > 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.
> > 3) %par r for range.
>
> Yes. I got it.
>
> Well, is struct range really used for addresses?

Commonly yes. But I agree with Andy that it is not always.

> It rather looks like
> a range of any 64-bit values.
>
> > %p[rR] is taken. %pra confuses things IMO.
>
> Another variants might be %pr64 or %prange.
>
> IMHO, there is no good solution. We are trying to find the least
> bad one. The meaning should be as obvious and as least confusing
> as possible.

Yep.

>
> Honestly, I do not have a strong opinion. I kind of like %prange ;-)
> But I could live with all other variants, except for %pn mentioned below.
>
> > > > 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.
>
> How exactly does it break the convention, please?
>
> Do you passing a pointer to struct range instead of a pointer to
> struct resource?

Yes a pointer is passed as the parameter. This is what %p means AFAIU.
Then the modifier is applied to know what we are pointing to.

>
> It should not be a big problem as long as the vsprintf() code is
> able to guess the right pointer type from the %pXX modifier.
>
> > The other idea I had, mentioned in the commit
> > message was %pn. Meaning passed by pointer 'raNge'.
>
> This looks like the worst variant to me.

Fair enough.

>
> > > 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);
> > +
> > + *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';
> > +
> > + return string_nocheck(buf, end, sym, spec);
> > +}
>
> I agree that there is not much duplicated code in the end.
>
> > 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? 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.
>
> This would be nasty. I believe that this is not what Andy meant.

Nope.

>
> Best Regards,
> Petr
>
> PS: I have vacation until the end of the week, so my next eventual
> reaction would be delayed.

No hurry. I'm still mucking around with it,
Ira