Instead of only iterating over the set of known SDT probes when sdt.ko is

loaded and unloaded, also have sdt.ko register callbacks with kern_sdt.c
that will be called when a newly loaded KLD module adds more probes or
a module with probes is unloaded.

This fixes two issues: first, if a module with SDT probes was loaded after
sdt.ko was loaded, those new probes would not be available in DTrace.
Second, if a module with SDT probes was unloaded while sdt.ko was loaded,
the kernel would panic the next time DTrace had cause to try and do
anything with the no-longer-existent probes.

This makes it possible to create SDT probes in KLD modules, although there
are still two caveats: first, any SDT probes in a KLD module must be part
of a DTrace provider that is defined in that module.  At present DTrace
only destroys probes when the provider is destroyed, so you can still
panic the system if a KLD module creates new probes in a provider from a
different module(including the kernel) and then unload the the first module.

Second, the system will panic if you unload a module containing SDT probes
while there is an active D script that has enabled those probes.

MFC after:	1 month

1 files changed, 4 insertions, 0 deletions

diff --git a/sys/sys/sdt.h b/sys/sys/sdt.h
index 3ee18a8..90d1699 100644
--- a/sys/sys/sdt.h
+++ b/sys/sys/sdt.h
@@ -258,6 +258,10 @@ int sdt_argtype_listall(struct sdt_probe *, sdt_argtype_listall_func_t, void *);
 int sdt_probe_listall(struct sdt_provider *, sdt_probe_listall_func_t, void *);
 int sdt_provider_listall(sdt_provider_listall_func_t,void *);
 
+void sdt_register_callbacks(sdt_provider_listall_func_t, void *,
+    sdt_provider_listall_func_t, void *, sdt_probe_listall_func_t, void *);
+void sdt_deregister_callbacks(void);
+
 #endif /* KDTRACE_HOOKS */
 
 #endif /* _KERNEL */