On Tue, Mar 26, 2024 at 08:15:56PM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@xxxxxxxxx>
>
> The way __print_symbolic() works is limited and inefficient
> in multiple ways:
> - you can only use it with a static list of symbols, but
> e.g. the SKB dropreasons are now a dynamic list
>
> - it builds the list in memory _three_ times, so it takes
> a lot of memory:
> - The print_fmt contains the list (since it's passed to
> the macro there). This actually contains the names
> _twice_, which is fixed up at runtime.
> - TRACE_DEFINE_ENUM() puts a 24-byte struct trace_eval_map
> for every entry, plus the string pointed to by it, which
> cannot be deduplicated with the strings in the print_fmt
> - The in-kernel symbolic printing creates yet another list
> of struct trace_print_flags for trace_print_symbols_seq()
>
> - it also requires runtime fixup during init, which is a lot
> of string parsing due to the print_fmt fixup
>
> Introduce __print_sym() to - over time - replace the old one.
> We can easily extend this also to __print_flags later, but I
> cared only about the SKB dropreasons for now, which has only
> __print_symbolic().
>
> This new __print_sym() requires only a single list of items,
> created by TRACE_DEFINE_SYM_LIST(), or can even use another
> already existing list by using TRACE_DEFINE_SYM_FNS() with
> lookup and show methods.
>
> Then, instead of doing an init-time fixup, just do this at the
> time when userspace reads the print_fmt. This way, dynamically
> updated lists are possible.
>
> For userspace, nothing actually changes, because the print_fmt
> is shown exactly the same way the old __print_symbolic() was.
>
> This adds about 4k .text in my test builds, but that'll be
> more than paid for by the actual conversions.
>
> Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Hi Johannes,
I'm seeing some allmodconfig build problems with this applied on top of
net-next.
In file included from ./include/trace/trace_events.h:27,
from ./include/trace/define_trace.h:102,
from ./include/trace/events/module.h:134,
from kernel/module/main.c:64:
./include/trace/stages/init.h:30: warning: "TRACE_DEFINE_SYM_FNS" redefined
30 | #define TRACE_DEFINE_SYM_FNS(_symbol_id, _lookup, _show) \
|
In file included from ./include/linux/trace_events.h:11,
from kernel/module/main.c:14:
./include/linux/tracepoint.h:130: note: this is the location of the previous definition
130 | #define TRACE_DEFINE_SYM_FNS(...)
|
./include/trace/stages/init.h:54: warning: "TRACE_DEFINE_SYM_LIST" redefined
54 | #define TRACE_DEFINE_SYM_LIST(_symbol_id, ...) \
|
./include/linux/tracepoint.h:131: note: this is the location of the previous definition
131 | #define TRACE_DEFINE_SYM_LIST(...)
|
