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

Ira Weiny
2024-08-22T17:53:43Z

Petr Mladek wrote:
> On Fri 2024-08-16 09:44:10, Ira Weiny wrote:
> > The use of struct range in the CXL subsystem is growing. In particular,
> > the addition of Dynamic Capacity devices uses struct range in a number
> > of places which are reported in debug and error messages.
> >
> > To wit requiring the printing of the start/end fields in each print
> > became cumbersome. Dan Williams mentions in [1] that it might be time
> > to have a print specifier for struct range similar to struct resource
> >
> > A few alternatives were considered including '%pn' for 'print raNge' but
> > %par follows that struct range is most often used to store a range of
> > physical addresses. So use '%par' for 'print address range'.
> >
> > --- a/Documentation/core-api/printk-formats.rst
> > +++ b/Documentation/core-api/printk-formats.rst
> > @@ -231,6 +231,20 @@ width of the CPU data path.
> >
> > Passed by reference.
> >
> > +Struct Range
> > +------------
> > +
> > +::
> > +
> > + %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.

>
> > + [range 0x0000000060000000-0x000000006fffffff]
> > +
> > +For printing struct range. A variation of printing a physical address is to
> > +print the value of struct range which are often used to hold a physical address
> > +range.
> > +
> > +Passed by reference.
> > +
> > DMA address types dma_addr_t
> > ----------------------------
> >
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 2d71b1115916..c132178fac07 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -1140,6 +1140,39 @@ char *resource_string(char *buf, char *end, struct resource *res,
> > return string_nocheck(buf, end, sym, spec);
> > }
> >
> > +static noinline_for_stack
> > +char *range_string(char *buf, char *end, const struct range *range,
> > + struct printf_spec spec, const char *fmt)
> > +{
> > +#define RANGE_PRINTK_SIZE 16
> > +#define RANGE_DECODED_BUF_SIZE ((2 * sizeof(struct range)) + 4)
> > +#define RANGE_PRINT_BUF_SIZE sizeof("[range - ]")
>
> I think that it should be "[range -]"

Sounds good.

>
> > + char sym[RANGE_DECODED_BUF_SIZE + RANGE_PRINT_BUF_SIZE];
> > + char *p = sym, *pend = sym + sizeof(sym);
> > +
> > + static const struct printf_spec str_spec = {
> > + .field_width = -1,
> > + .precision = 10,
> > + .flags = LEFT,
> > + };
>
> Is this really needed? What about using "default_str_spec" instead?

Because I got confused and was coping from resource_string().

Deleted now...

>
> > + static const struct printf_spec range_spec = {
> > + .base = 16,
> > + .field_width = RANGE_PRINTK_SIZE,

However, my testing indicates this needs to be.

.field_width = 18, /* 2 (0x) + 2 * 8 (bytes) */

... to properly zero pad the value. Does that make sense?

> > + .precision = -1,
> > + .flags = SPECIAL | SMALL | ZEROPAD,
> > + };
> > +
> > + *p++ = '[';
> > + p = string_nocheck(p, pend, "range ", str_spec);
> > + p = number(p, pend, range->start, range_spec);
> > + *p++ = '-';
> > + p = number(p, pend, range->end, range_spec);
> > + *p++ = ']';
> > + *p = '\0';
> > +
> > + return string_nocheck(buf, end, sym, spec);
> > +}
> > +
> > static noinline_for_stack
> > char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
> > const char *fmt)
>
> Also add a selftest into lib/test_printf.c, please.

Yes of course... Makes testing easier too.

Thanks,
Ira

>
> Best Regards,
> Petr