Re: Another Obsolete Fix me in trace.h?

Re: Another Obsolete Fix me in trace.h?

[Paolo Bonzini]

On 24/11/2014 05:36, nick wrote:
> Greetings Again Gleb and others,
> I am assuming in the code I am pasting below the fix me is obsolete now and I can remove it. :)
> Cheers Nick
> TP_printk("%s (0x%x)",
>                   __print_symbolic(__entry->exception, kvm_trace_sym_exc),
>                    /* FIXME: don't print error_code if not present */
>                   __entry->has_error ? __entry->error_code : 0)
> );
> 

No, it's not obsolete, the idea is to print only

   %s

instead of

   %s (0x%x)

if __entry->has_error is false.  I don't know the trace API well enough
to know if that is possible.

Paolo

Re: Another Obsolete Fix me in trace.h?

[Jan Kiszka]

On 2014-11-24 11:12, Paolo Bonzini wrote:
> On 24/11/2014 05:36, nick wrote:
>> Greetings Again Gleb and others,
>> I am assuming in the code I am pasting below the fix me is obsolete now and I can remove it. :)
>> Cheers Nick
>> TP_printk("%s (0x%x)",
>>                   __print_symbolic(__entry->exception, kvm_trace_sym_exc),
>>                    /* FIXME: don't print error_code if not present */
>>                   __entry->has_error ? __entry->error_code : 0)
>> );
>>
> 
> No, it's not obsolete, the idea is to print only
> 
>    %s
> 
> instead of
> 
>    %s (0x%x)
> 
> if __entry->has_error is false.  I don't know the trace API well enough
> to know if that is possible.

Last time I ran across such a scenario, it was not feasible and
essentially required separate tracepoints. But maybe Steven knows a trick.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux

Re: Another Obsolete Fix me in trace.h?

[Radim Krčmář]

2014-11-24 11:40+0100, Jan Kiszka:
> On 2014-11-24 11:12, Paolo Bonzini wrote:
> > On 24/11/2014 05:36, nick wrote:
> >> Greetings Again Gleb and others,
> >> I am assuming in the code I am pasting below the fix me is obsolete now and I can remove it. :)
> >> Cheers Nick
> >> TP_printk("%s (0x%x)",
> >>                   __print_symbolic(__entry->exception, kvm_trace_sym_exc),
> >>                    /* FIXME: don't print error_code if not present */
> >>                   __entry->has_error ? __entry->error_code : 0)
> >> );
> >>
> > 
> > No, it's not obsolete, the idea is to print only
> > 
> >    %s
> > 
> > instead of
> > 
> >    %s (0x%x)
> > 
> > if __entry->has_error is false.  I don't know the trace API well enough
> > to know if that is possible.
> 
> Last time I ran across such a scenario, it was not feasible and
> essentially required separate tracepoints. But maybe Steven knows a trick.

The format string has to be a string literal[1]; we could change it to
allow expressions[2], but what we want is almost possible through a
direct call to trace_seq_printf()[3].

The raw result would look like

  #define __print(fmt, args...) ({ \
  	const char *buf_start = trace_seq_buffer_ptr(p); \
  	trace_seq_printf(p, fmt, args); \
  	trace_seq_putc(p, '\0'); \
  	buf_start; \
  	})

  TP_printk("%s%s", [...],
            __entry->has_error ? __print("(0x%x)", __entry->error_code) : "")

and would be acceptable if something __print-like made it into a ftrace
helper[4].  (Userspace won't be able to nicely print it otherwise.)


---
1: #define TP_printk(fmt, args...) fmt "\n", args
2: TP_printk(__entry->has_error ? "%s (0x%x)" : "%s", [...]
3: Already in scsi_dispatch_cmd_start or kvm_mmu_get_page tracepoints.
4: Like __print_hex or print_symbolic.

Re: Another Obsolete Fix me in trace.h?

[Steven Rostedt]

On Mon, 24 Nov 2014 22:00:01 +0100
Radim Krčmář <rkrcmar@redhat.com> wrote:

> 2014-11-24 11:40+0100, Jan Kiszka:
> > On 2014-11-24 11:12, Paolo Bonzini wrote:
> > > On 24/11/2014 05:36, nick wrote:
> > >> Greetings Again Gleb and others,
> > >> I am assuming in the code I am pasting below the fix me is obsolete now and I can remove it. :)
> > >> Cheers Nick
> > >> TP_printk("%s (0x%x)",
> > >>                   __print_symbolic(__entry->exception, kvm_trace_sym_exc),
> > >>                    /* FIXME: don't print error_code if not present */
> > >>                   __entry->has_error ? __entry->error_code : 0)
> > >> );
> > >>
> > > 
> > > No, it's not obsolete, the idea is to print only
> > > 
> > >    %s
> > > 
> > > instead of
> > > 
> > >    %s (0x%x)
> > > 
> > > if __entry->has_error is false.  I don't know the trace API well enough
> > > to know if that is possible.
> > 
> > Last time I ran across such a scenario, it was not feasible and
> > essentially required separate tracepoints. But maybe Steven knows a trick.
> 
> The format string has to be a string literal[1]; we could change it to
> allow expressions[2], but what we want is almost possible through a
> direct call to trace_seq_printf()[3].
> 
> The raw result would look like
> 
>   #define __print(fmt, args...) ({ \
>   	const char *buf_start = trace_seq_buffer_ptr(p); \
>   	trace_seq_printf(p, fmt, args); \
>   	trace_seq_putc(p, '\0'); \
>   	buf_start; \
>   	})
> 
>   TP_printk("%s%s", [...],
>             __entry->has_error ? __print("(0x%x)", __entry->error_code) : "")
> 
> and would be acceptable if something __print-like made it into a ftrace
> helper[4].  (Userspace won't be able to nicely print it otherwise.)

You mean if we add something like a __print_conditional(cond, fmt, ...);

For this case you would have:

  TP_printk("%s%s", [...],
	__print_conditional(__entry->has_error, " (0x%x)", __entry->error_code));

Where __print_conditional() will return "" when "cond" is false, and
will return the formatted string otherwise.

That wouldn't be too hard to implement.

-- Steve


> 
> 
> ---
> 1: #define TP_printk(fmt, args...) fmt "\n", args
> 2: TP_printk(__entry->has_error ? "%s (0x%x)" : "%s", [...]
> 3: Already in scsi_dispatch_cmd_start or kvm_mmu_get_page tracepoints.
> 4: Like __print_hex or print_symbolic.

Re: Another Obsolete Fix me in trace.h?

[Radim Krčmář]

2014-11-24 16:19-0500, Steven Rostedt:
> On Mon, 24 Nov 2014 22:00:01 +0100
> Radim Krčmář <rkrcmar@redhat.com> wrote:
> 
> > 2014-11-24 11:40+0100, Jan Kiszka:
> > The format string has to be a string literal[1]; we could change it to
> > allow expressions[2], but what we want is almost possible through a
> > direct call to trace_seq_printf()[3].
> > 
> > The raw result would look like
> > 
> >   #define __print(fmt, args...) ({ \
> >   	const char *buf_start = trace_seq_buffer_ptr(p); \
> >   	trace_seq_printf(p, fmt, args); \
> >   	trace_seq_putc(p, '\0'); \
> >   	buf_start; \
> >   	})
> > 
> >   TP_printk("%s%s", [...],
> >             __entry->has_error ? __print("(0x%x)", __entry->error_code) : "")
> > 
> > and would be acceptable if something __print-like made it into a ftrace
> > helper[4].  (Userspace won't be able to nicely print it otherwise.)
> 
> You mean if we add something like a __print_conditional(cond, fmt, ...);

The benefit of _conditional is cleaner code?

(_conditional would be possible as a #define on top of generic print,
 the ternary seems to be parsed correctly.)

> For this case you would have:
> 
>   TP_printk("%s%s", [...],
> 	__print_conditional(__entry->has_error, " (0x%x)", __entry->error_code));
> 
> Where __print_conditional() will return "" when "cond" is false, and
> will return the formatted string otherwise.

(This might introduce 'const char empty[] = ""'.)

> That wouldn't be too hard to implement.

I'll look at the patch tommorrow.

Thanks.

Re: Another Obsolete Fix me in trace.h?

[Radim Krčmář]

2014-11-24 22:49+0100, Radim Krčmář:
> 2014-11-24 16:19-0500, Steven Rostedt:
> > That wouldn't be too hard to implement.
> 
> I'll look at the patch tommorrow.

The kernel part is trivial.
Most of the code is going to be in tools/lib/traceevent/event-parse.c.

I wasn't sure whether to
1) define new 'enum print_arg_type' for our function and do exactly what
   other __print* did
2) extend existing PRINT_FUNC with variable arguments and register it as
   a "global" event handler

as (2) makes more sense to me, but we already had it when some __print*
was implemented ... (and I didn't want to dig too deep into the project)

Re: Another Obsolete Fix me in trace.h?

[Steven Rostedt]

On Wed, 26 Nov 2014 13:40:26 +0100
Radim Krčmář <rkrcmar@redhat.com> wrote:

> 2014-11-24 22:49+0100, Radim Krčmář:
> > 2014-11-24 16:19-0500, Steven Rostedt:
> > > That wouldn't be too hard to implement.
> > 
> > I'll look at the patch tommorrow.
> 
> The kernel part is trivial.
> Most of the code is going to be in tools/lib/traceevent/event-parse.c.
> 
> I wasn't sure whether to
> 1) define new 'enum print_arg_type' for our function and do exactly what
>    other __print* did
> 2) extend existing PRINT_FUNC with variable arguments and register it as
>    a "global" event handler
> 
> as (2) makes more sense to me, but we already had it when some __print*
> was implemented ... (and I didn't want to dig too deep into the project)

Add a new hardcoded instance. The PRINT_FUNC is for plugins that have a
unique function for the events they handle. Notice that event-parse
does not define any func handlers. If this is to be generic, then lets
make it specified as a new enum.

Thanks,

-- Steve

Re: Another Obsolete Fix me in trace.h?

[Radim Krčmář]

2014-11-26 09:15-0500, Steven Rostedt:
> On Wed, 26 Nov 2014 13:40:26 +0100
> Radim Krčmář <rkrcmar@redhat.com> wrote:
> > The kernel part is trivial.
> > Most of the code is going to be in tools/lib/traceevent/event-parse.c.
> > 
> > I wasn't sure whether to
> > 1) define new 'enum print_arg_type' for our function and do exactly what
> >    other __print* did
> > 2) extend existing PRINT_FUNC with variable arguments and register it as
> >    a "global" event handler
> > 
> > as (2) makes more sense to me, but we already had it when some __print*
> > was implemented ... (and I didn't want to dig too deep into the project)
> 
> Add a new hardcoded instance. The PRINT_FUNC is for plugins that have a
> unique function for the events they handle. Notice that event-parse
> does not define any func handlers. If this is to be generic, then lets
> make it specified as a new enum.

Ok, thanks.

(It just seemed weird that we have an infrastructure that could allow a
 "generic plugin" to cover this functionality.)

Re: Another Obsolete Fix me in trace.h?

[Steven Rostedt]

On Wed, 26 Nov 2014 15:49:34 +0100
Radim Krčmář <rkrcmar@redhat.com> wrote:

 
> (It just seemed weird that we have an infrastructure that could allow a
>  "generic plugin" to cover this functionality.)

Maybe in the future we may do something like that. But for now, think
of these as "optimized" ;-)

-- Steve