ZFS SET_ERROR dtrace probe possible under FreeBSD?

Mark Johnston markj at FreeBSD.org
Tue Sep 16 16:39:50 UTC 2014 

On Tue, Sep 16, 2014 at 11:05:09AM +0100, Steven Hartland wrote:
> 
> ----- Original Message ----- 
> From: "Mark Johnston" <markj at FreeBSD.org>
> 
> 
> > On Mon, Sep 15, 2014 at 07:59:50PM -0700, Matthew Ahrens wrote:
> >> Disclaimer: I'm not an expert in FreeBSD dtrace.
> >> 
> >> It looks like the FreeBSD kernel uses these declaration for kernel SDT
> >> probes, in sdt.h:
> >> 
> >> 333 <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#333>#*define*
> >> DTRACE_PROBE1 <http://src.illumos.org/source/s?refs=DTRACE_PROBE1&project=freebsd-head>(name
> >> <http://src.illumos.org/source/s?defs=name&project=freebsd-head>,
> >> type0 <http://src.illumos.org/source/s?defs=type0&project=freebsd-head>,
> >> arg0 <http://src.illumos.org/source/s?defs=arg0&project=freebsd-head>) \334
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#334> DTRACE_PROBE_IMPL_START
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#DTRACE_PROBE_IMPL_START>(name
> >> <http://src.illumos.org/source/s?defs=name&project=freebsd-head>, arg0
> >> <http://src.illumos.org/source/s?defs=arg0&project=freebsd-head>, 0,
> >> 0, 0, 0) \335
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#335> SDT_PROBE_ARGTYPE
> >> <http://src.illumos.org/source/s?defs=SDT_PROBE_ARGTYPE&project=freebsd-head>(sdt
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#sdt>, ,
> >> , name <http://src.illumos.org/source/s?defs=name&project=freebsd-head>,
> >> 0, #type0 <http://src.illumos.org/source/s?defs=type0&project=freebsd-head>,
> >> NULL <http://src.illumos.org/source/s?defs=NULL&project=freebsd-head>); \336
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#336> DTRACE_PROBE_IMPL_END
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#DTRACE_PROBE_IMPL_END>
> >> 
> >> 
> >> 324 <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#324>#*define* DTRACE_PROBE_IMPL_START
> >> <http://src.illumos.org/source/s?refs=DTRACE_PROBE_IMPL_START&project=freebsd-head>(name
> >> <http://src.illumos.org/source/s?defs=name&project=freebsd-head>, arg0
> >> <http://src.illumos.org/source/s?defs=arg0&project=freebsd-head>, arg1
> >> <http://src.illumos.org/source/s?defs=arg1&project=freebsd-head>, arg2
> >> <http://src.illumos.org/source/s?defs=arg2&project=freebsd-head>, arg3
> >> <http://src.illumos.org/source/s?defs=arg3&project=freebsd-head>, arg4
> >> <http://src.illumos.org/source/s?defs=arg4&project=freebsd-head>) *do*
> >> { \325 <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#325> *static*
> >> SDT_PROBE_DEFINE
> >> <http://src.illumos.org/source/s?defs=SDT_PROBE_DEFINE&project=freebsd-head>(sdt
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#sdt>, ,
> >> , name <http://src.illumos.org/source/s?defs=name&project=freebsd-head>); 
> >>     \326 <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#326> SDT_PROBE
> >> <http://src.illumos.org/source/s?defs=SDT_PROBE&project=freebsd-head>(sdt
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#sdt>, ,
> >> , name <http://src.illumos.org/source/s?defs=name&project=freebsd-head>,
> >> arg0 <http://src.illumos.org/source/s?defs=arg0&project=freebsd-head>,
> >> arg1 <http://src.illumos.org/source/s?defs=arg1&project=freebsd-head>,
> >> arg2 <http://src.illumos.org/source/s?defs=arg2&project=freebsd-head>,
> >> arg3 <http://src.illumos.org/source/s?defs=arg3&project=freebsd-head>,
> >> arg4 <http://src.illumos.org/source/s?defs=arg4&project=freebsd-head>);327
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#327>#*define*
> >> DTRACE_PROBE_IMPL_END
> >> <http://src.illumos.org/source/s?refs=DTRACE_PROBE_IMPL_END&project=freebsd-head> }
> >> *while* (0)
> >> 
> >> 
> >> 163 <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#163>#*define*
> >> SDT_PROBE <http://src.illumos.org/source/s?refs=SDT_PROBE&project=freebsd-head>(prov
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#prov>,
> >> mod <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#mod>,
> >> func <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#func>,
> >> name <http://src.illumos.org/source/s?defs=name&project=freebsd-head>,
> >> arg0 <http://src.illumos.org/source/s?defs=arg0&project=freebsd-head>,
> >> arg1 <http://src.illumos.org/source/s?defs=arg1&project=freebsd-head>,
> >> arg2 <http://src.illumos.org/source/s?defs=arg2&project=freebsd-head>,
> >> arg3 <http://src.illumos.org/source/s?defs=arg3&project=freebsd-head>,
> >> arg4 <http://src.illumos.org/source/s?defs=arg4&project=freebsd-head>) *do*
> >> { \164 <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#164> *if*
> >> (sdt_ <http://src.illumos.org/source/s?defs=sdt_&project=freebsd-head>##prov
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#prov>##_##mod
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#mod>##_##func
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#func>##_##name
> >> <http://src.illumos.org/source/s?defs=name&project=freebsd-head>->id
> >> <http://src.illumos.org/source/s?defs=id&project=freebsd-head>) \165
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#165> (*sdt_probe_func
> >> <http://src.illumos.org/source/s?defs=sdt_probe_func&project=freebsd-head>)(sdt_
> >> <http://src.illumos.org/source/s?defs=sdt_&project=freebsd-head>##prov
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#prov>##_##mod
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#mod>##_##func
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#func>##_##name
> >> <http://src.illumos.org/source/s?defs=name&project=freebsd-head>->id
> >> <http://src.illumos.org/source/s?defs=id&project=freebsd-head>, \166
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#166> 
> >>   (uintptr_t <http://src.illumos.org/source/s?defs=uintptr_t&project=freebsd-head>)
> >> arg0 <http://src.illumos.org/source/s?defs=arg0&project=freebsd-head>,
> >> (uintptr_t <http://src.illumos.org/source/s?defs=uintptr_t&project=freebsd-head>)
> >> arg1 <http://src.illumos.org/source/s?defs=arg1&project=freebsd-head>,
> >> (uintptr_t <http://src.illumos.org/source/s?defs=uintptr_t&project=freebsd-head>)
> >> arg2 <http://src.illumos.org/source/s?defs=arg2&project=freebsd-head>, \167
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#167> 
> >>   (uintptr_t <http://src.illumos.org/source/s?defs=uintptr_t&project=freebsd-head>)
> >> arg3 <http://src.illumos.org/source/s?defs=arg3&project=freebsd-head>,
> >> (uintptr_t <http://src.illumos.org/source/s?defs=uintptr_t&project=freebsd-head>)
> >> arg4 <http://src.illumos.org/source/s?defs=arg4&project=freebsd-head>); \168
> >> <http://src.illumos.org/source/xref/freebsd-head/sys/sys/sdt.h#168>}
> >> *while* (0)
> >> 
> >> 
> >> To do the equivalent "extra static" magic, you will need to expand out the
> >> DTRACE_PROBE1 macro.  I think it should look something like:
> >> 
> >> SDT_PROBE_DEFINE1(sdt, zfs, , set__error, "int");
> >> 
> >> #define SET_ERROR(err) \
> >>     ((sdt_sdt_zfs__set__error->id && \
> >>     (*sdt_probe_func)(sdt_sdt_zfs__set__error->id, (uintptr_t)err, 0, 0, 0,
> >> 0)), \
> >>     err)
> > 
> > I think it would need to be
> > 
> >  SDT_PROBE_DECLARE(sdt, , , set__error);
> > 
> >  #define SET_ERROR(err) ...
> > 
> > in the compat sdt.h, and then kern_dtrace.c or so would contain
> > 
> >  SDT_PROBE_DEFINE1(sdt, , , set__error, "int");
> > 
> > Note that the module shouldn't be hard-coded - it'll be filled in when
> > the probes are created by the SDT code.
> 
> Thanks guys for the pointers, I tried the following slightly ammended
> from Matts original due to sdt_probe_func being a void return:
> 
> Index: sys/cddl/compat/opensolaris/sys/sdt.h
> ===================================================================
> --- sys/cddl/compat/opensolaris/sys/sdt.h       (revision 271518)
> +++ sys/cddl/compat/opensolaris/sys/sdt.h       (working copy)
> @@ -34,6 +34,11 @@
>  #endif
>  #include_next <sys/sdt.h>
>  
> -#define        SET_ERROR(err)  (err)
> +SDT_PROBE_DECLARE(sdt, , , set__error);
>  
> +#define SET_ERROR(err) \
> +       ((sdt_sdt___set__error->id ? \
> +       (*sdt_probe_func)(sdt_sdt___set__error->id, \
> +           (uintptr_t)err, 0, 0, 0, 0) : 0), err)
> +
>  #endif /* _OPENSOLARIS_SYS_SDT_H_ */
> Index: sys/kern/kern_dtrace.c
> ===================================================================
> --- sys/kern/kern_dtrace.c      (revision 271518)
> +++ sys/kern/kern_dtrace.c      (working copy)
> @@ -48,6 +48,8 @@ FEATURE(kdtrace_hooks,
>  
>  static MALLOC_DEFINE(M_KDTRACE, "kdtrace", "DTrace hooks");
>  
> +SDT_PROBE_DEFINE1(sdt, , , set__error, "int");
> +
>  /* Hooks used in the machine-dependent trap handlers. */
>  dtrace_trap_func_t             dtrace_trap_func;
>  dtrace_doubletrap_func_t       dtrace_doubletrap_func;
> 
> But it fails with:-
> /usr/src/sys/kern/kern_dtrace.c:51:24: error: expected identifier
> SDT_PROBE_DEFINE1(sdt, , , set__error, "int");
>                        ^
> /usr/src/sys/kern/kern_dtrace.c:51:1: error: type specifier missing, defaults to 'int' [-Werror,-Wimplicit-int]
> SDT_PROBE_DEFINE1(sdt, , , set__error, "int");
> 
> All other calls to SDT_PROBE_DEFINE1 seem to define all args e.g.
> sys/kern/kern_exit.c:SDT_PROBE_DEFINE1(proc, kernel, , exit, "int");
> 
> Are you sure they should be ommited?

You'll need to #include <sys/sdt.h> in kern_dtrace.c.

> 
> Also is kern_dtrace.c the correct place for the probe define given
> its zfs specific?

I was just thinking that it might be useful elsewhere too.

For now, perhaps the best place is in a new file under
sys/cddl/compat/opensolaris/kern. Then it'll be part of opensolaris.ko
and SET_ERROR will work for any illumos code in the tree, not just ZFS.

-Mark

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