On Sun, Apr 04, 2021 at 01:22:23AM +0200, Klemens Nanni wrote:
> print(9) says it only documents differences and points at printf(3) for
> identical/shared bits:
>
> DESCRIPTION
> [...]
>
> Since each of these kernel functions is a variant of its user space
> counterpart, this page describes only the differences between the user
> space and kernel versions. Refer to printf(3) for functional details.
>
> FORMAT OPTIONS
> The kernel functions don't support as many formatting specifiers as their
> user space counterparts. In addition to the floating point formatting
> specifiers, the following integer type specifiers are not supported:
>
> %hh Argument of char type. This format specifier is accepted by the
> kernel but will be handled as %h.
>
> %j Argument of intmax_t or uintmax_t type.
>
> %t Argument of ptrdiff_t type.
>
> The kernel functions support some additional formatting specifiers:
>
> %b Bit field expansion. [...]
>
>
> So reading this, I get the impression that print(3)'s entire conversion
> specifications syntax is supported (merely with a few less `conversion'
> specifiers):
>
> %[argno$][flags][width][.precision][size]conversion
>
> but printf(9) supports much fewer specifiers, afaict amounting to
>
> %[width][size]conversion
>
> That's fine, but code using printf(3) syntax might actually compile
> without warnings (like this example did for me) and be useless afterall:
>
> + printf("%1$s: node %2$x:\n"
> + " mclk_rate is %3$u (0x%3$x)\n",
> + __func__, sc->sc_node, mclk_rate);
>
> Apr 4 00:32:29 pine64 /bsd: mclk_rate is $u (0x $x)
>
>
> I don't fancy expanding syntax or adding checks to the kernel's printf.c
> but documenting it seems needed.
>
> Feedback? Objections? OK?
>
> diff 5b147494c5d594d5ec97ca57686c9e3527b87e29 /usr/src
> blob - c31fb0cb42e9af426c42306a54339ec7f7f375a7
> file + share/man/man9/printf.9
> --- share/man/man9/printf.9
> +++ share/man/man9/printf.9
> @@ -119,6 +119,17 @@ send formatted strings to the ddb console, and are onl
> Since each of these kernel functions is a variant of its user space
> counterpart, this page describes only the differences between the user
> space and kernel versions.
> +.Pp
> +The limited syntax of a conversion specification is:
hi. i'm fine with your diff, though cannot really judge the actual
content. but the "limited syntax" text is a bit ambiguous. you could
still expect from it that a full syntax version is supported.
maybe spell it out?
printf(9) supports a subset of the conversion specification
available to printf(3):
sth like that?
jmc
> +.Bd -filled -offset indent
> +.Sm off
> +.Cm %
> +.Op Ar width
> +.Op Ar size
> +.Ar conversion
> +.Sm on
> +.Ed
> +.Pp
> Refer to
> .Xr printf 3
> for functional details.
>
