Date: Mon, 15 Sep 2014 20:13:19 -0700 From: Mark Johnston <markj@FreeBSD.org> To: Matthew Ahrens <mahrens@delphix.com> Cc: Steven Hartland <smh@freebsd.org>, hackers@freebsd.org, freebsd-dtrace@freebsd.org Subject: Re: ZFS SET_ERROR dtrace probe possible under FreeBSD? Message-ID: <20140916031318.GB26720@charmander.picturesperfect.net> In-Reply-To: <CAJjvXiF4kPFW--SioqAvR%2BF1kwMgYUkfGqtLd4ZHh0jWhrNN5Q@mail.gmail.com> References: <AEC968EBE6DE4E56A76DD7578DC25483@multiplay.co.uk> <CAJjvXiF4kPFW--SioqAvR%2BF1kwMgYUkfGqtLd4ZHh0jWhrNN5Q@mail.gmail.com>
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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. -Mark > > Note that SET_ERROR is an expansion of SDT_PROBE, but rewritten to be a > single statement, so that we can do the same trick with the comma operator. > > --matt > > On Mon, Sep 15, 2014 at 7:03 PM, Steven Hartland <smh@freebsd.org> wrote: > > > The following commit added SET_ERROR dtrace probes to illumos > > https://github.com/illumos/illumos-gate/commit/be6fd75 > > > > Now we have all the SET_ERROR calls but the FreeBSD's ZFS implementation > > but our SET_ERROR in sys/cddl/compat/opensolaris/sys/sdt.h is simply: > > #define SET_ERROR(err) (err) > > > > I tried using the illumos version but that resulted being unable > > to mount ZFS root, so clearly not right. > > > > /* > > * the set-error SDT probe is extra static, in that we declare its fake > > * function literally, rather than with the DTRACE_PROBE1() macro. This is > > * necessary so that SET_ERROR() can evaluate to a value, which wouldn't > > * be possible if it required multiple statements (to declare the function > > * and then call it). > > * > > * SET_ERROR() uses the comma operator so that it can be used without much > > * additional code. For example, "return (EINVAL);" becomes > > * "return (SET_ERROR(EINVAL));". Note that the argument will be evaluated > > * twice, so it should not have side effects (e.g. something like: > > * "return (SET_ERROR(log_error(EINVAL, info)));" would log the error > > twice). > > */ > > extern void __dtrace_probe_set__error(uintptr_t); > > #define SET_ERROR(err) (__dtrace_probe_set__error(err), err) > > > > > > For those that know the the ins and outs of our dtrace is it > > possible for us to add support for this trace point? > > > > Regards > > Steve
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