On Wed 2024-02-28 09:32:37, Rasmus Villemoes wrote:
> On 27/02/2024 19.32, Ville Syrjälä wrote:
> > On Tue, Feb 27, 2024 at 10:38:10AM +0100, Rasmus Villemoes wrote:
> >> On 26/02/2024 15.57, Jani Nikula wrote:
> So if we really want to go down this road, I think it should be
> something like %pX{drm:whatever}, with core printf just looking up the
> token "drm" in a run-time list of registered callbacks (because I don't
> want vsprintf.c filled with random subsystems' formatting code), and
> that single callback would then be handed a pointer to the rest of the
> format string (i.e. the "whatever}..."), the pointer argument from the
> varargs, and the buf,end pair. But then we're back to trusting that
> callback (which might of course multiplex based on the "whatever" part)
> to behave correctly. And then we might as well avoid the string parsing
> and just do the "callback + pointer" in one struct (passed as pointer to
> compound literal), which also avoids the tricky "what to do about module
> unload versus unregistering of callbacks" etc.
Mathew Wilcox had the idea to introduce a structure:
struct printf_state {
char *buf;
char *end;
void *ptr;
};
Where *ptr would point to some data which should be printed,
same as wee pass to the %pbla now.
Then allow to implement:
char *my_func(struct printf_state *ps, void *ptr);
and use it as:
printk("%pX(%p)\n", my_func, ptr);
One problem here is type checking of the data passed via *ptr
but we already have the same problem now.
Another problem is how to make sure that the function is safe.
A solution might be to implement an API for appending characters,
strings, numbers, ... Similar to seq_buf() API.
AFAIK, the result was to actually use the existing seq_buf API
to format the string. AFAIK, it motivated:
+ commit 96928d9032a7c34f1 ("seq_buf: Add seq_buf_do_printk() helper")
and probably also
+ commit d0ed46b60396cfa7 ("tracing: Move readpos from seq_buf to trace_seq")
and also this one is pretty useful:
+ commit dcc4e5728eeaeda8 ("seq_buf: Introduce DECLARE_SEQ_BUF and
seq_buf_str()")
And it motivated:
+ commit dcc4e5728eeaeda84878ca0 ("seq_buf: Introduce
DECLARE_SEQ_BUF and seq_buf_str()")
Best Regards,
Petr
