by Chuck Lever III

[permalink] [raw]

Subject: Re: [PATCH v2 01/25] NFSD: Fix TP_printk() format specifier in trace_nfsd_dirent()

Hello Steven-

> On May 13, 2021, at 10:50 AM, Steven Rostedt <[email protected]> wrote:
>
> On Wed, 12 May 2021 16:52:05 +0000
> Chuck Lever III <[email protected]> wrote:
>
>> The underlying need is to support non-NUL-terminated C strings.
>>
>> I assumed that since the commentary around 9a6944fee68e claims
>> the proper way to trace C strings is to use __string and friends,
>> and those do not support non-NUL-terminated strings, that such
>> strings are really not first-class citizens. Thus I concluded
>> that my use of '%.*s' was incorrect.
>>
>> Having some __string-style helpers that can deal with such
>> strings would be valuable.
>
> I guess the best I can do is a strncpy version, that will add the '\0' in
> the ring buffer. That way we don't need to save the length as well (length
> would need to be at least 4 bytes, where as '\0' is one).
>
> Something like this?

I don't see this change in v5.14-rc1.

> I added "__string_len()" and "__assign_str_len()". You use them just like
> __string() and __assign_str() but add a max length that you want to use
> (although, it will always allocate "len" regardless if the string is
> smaller). Then use __get_str() just like you use __string().
>
> Would something like that work?
>
> -- Steve
>
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 8268bf747d6f..7ab23535a0c8 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -102,6 +102,9 @@ TRACE_MAKE_SYSTEM_STR();
> #undef __string
> #define __string(item, src) __dynamic_array(char, item, -1)
>
> +#undef __string_len
> +#define __string_len(item, src, len) __dynamic_array(char, item, -1)
> +
> #undef __bitmask
> #define __bitmask(item, nr_bits) __dynamic_array(char, item, -1)
>
> @@ -197,6 +200,9 @@ TRACE_MAKE_SYSTEM_STR();
> #undef __string
> #define __string(item, src) __dynamic_array(char, item, -1)
>
> +#undef __string_len
> +#define __string_len(item, src, len) __dynamic_array(char, item, -1)
> +
> #undef __bitmask
> #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
>
> @@ -444,6 +450,9 @@ static struct trace_event_functions trace_event_type_funcs_##call = { \
> #undef __string
> #define __string(item, src) __dynamic_array(char, item, -1)
>
> +#undef __string_len
> +#define __string_len(item, src, len) __dynamic_array(char, item, -1)
> +
> #undef __bitmask
> #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
>
> @@ -492,6 +501,9 @@ static struct trace_event_fields trace_event_fields_##call[] = { \
> #define __string(item, src) __dynamic_array(char, item, \
> strlen((src) ? (const char *)(src) : "(null)") + 1)
>
> +#undef __string_len
> +#define __string_len(item, src, len) __dynamic_array(char, item, (len) + 1)
> +
> /*
> * __bitmask_size_in_bytes_raw is the number of bytes needed to hold
> * num_possible_cpus().
> @@ -655,10 +667,18 @@ static inline notrace int trace_event_get_offsets_##call( \
> #undef __string
> #define __string(item, src) __dynamic_array(char, item, -1)
>
> +#undef __string_len
> +#define __string_len(item, src, len) __dynamic_array(char, item, -1)
> +
> #undef __assign_str
> #define __assign_str(dst, src) \
> strcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)");
>
> +#undef __assign_str_len
> +#define __assign_str_len(dst, src, len) \
> + strncpy(__get_str(dst), (src) ? (const char *)(src) : "(null)", len); \
> + __get_str(dst)[len] = '\0';
> +
> #undef __bitmask
> #define __bitmask(item, nr_bits) __dynamic_array(unsigned long, item, -1)
>
>
>

--
Chuck Lever

2021-07-12 17:10:16

by Steven Rostedt

[permalink] [raw]

Subject: Re: [PATCH v2 01/25] NFSD: Fix TP_printk() format specifier in trace_nfsd_dirent()

On Mon, 12 Jul 2021 15:18:05 +0000
Chuck Lever III <[email protected]> wrote:

> Hello Steven-
>
> > On May 13, 2021, at 10:50 AM, Steven Rostedt <[email protected]> wrote:
> >
> > On Wed, 12 May 2021 16:52:05 +0000
> > Chuck Lever III <[email protected]> wrote:
> >
> >> The underlying need is to support non-NUL-terminated C strings.
> >>
> >> I assumed that since the commentary around 9a6944fee68e claims
> >> the proper way to trace C strings is to use __string and friends,
> >> and those do not support non-NUL-terminated strings, that such
> >> strings are really not first-class citizens. Thus I concluded
> >> that my use of '%.*s' was incorrect.
> >>
> >> Having some __string-style helpers that can deal with such
> >> strings would be valuable.
> >
> > I guess the best I can do is a strncpy version, that will add the '\0' in
> > the ring buffer. That way we don't need to save the length as well (length
> > would need to be at least 4 bytes, where as '\0' is one).
> >
> > Something like this?
>
> I don't see this change in v5.14-rc1.

Grumble.

I thought this thread was over with the bug fix that was sent, but
completely forgot about this change, as I never made it into a real commit.

I can add this now, kick off some tests, and grovel to Linus saying that
this is unused code, but other code will depend on this, and I want to get
it upstream so that it can.

-- Steve
>
>
> > I added "__string_len()" and "__assign_str_len()". You use them just like
> > __string() and __assign_str() but add a max length that you want to use
> > (although, it will always allocate "len" regardless if the string is
> > smaller). Then use __get_str() just like you use __string().
> >
> > Would something like that work?
> >
> > -- Steve
> >