Enable use of DTRACE_PROBE* macros in "spl" module

This change modifies some of the infrastructure for enabling the use of
the DTRACE_PROBE* macros, such that we can use tehm in the "spl" module.

Currently, when the DTRACE_PROBE* macros are used, they get expanded to
create new functions, and these dynamically generated functions become
part of the "zfs" module.

Since the "spl" module does not depend on the "zfs" module, the use of
DTRACE_PROBE* in the "spl" module would result in undefined symbols
being used in the "spl" module. Specifically, DTRACE_PROBE* would turn
into a function call, and the function being called would be a symbol
only contained in the "zfs" module; which results in a linker and/or
runtime error.

Thus, this change adds the necessary logic to the "spl" module, to
mirror the tracing functionality available to the "zfs" module. After
this change, we'll have a "trace_zfs.h" header file which defines the
probes available only to the "zfs" module, and a "trace_spl.h" header
file which defines the probes available only to the "spl" module.

Reviewed by: Brad Lewis <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Prakash Surya <[email protected]>
Closes #9525

3 files changed, 26 insertions, 1 deletions

diff --git a/lib/libspl/include/sys/Makefile.am b/lib/libspl/include/sys/Makefile.am
index d84ed1ec4..a83fc025e 100644
--- a/lib/libspl/include/sys/Makefile.am
+++ b/lib/libspl/include/sys/Makefile.am
@@ -35,7 +35,8 @@ libspl_HEADERS = \
 	$(top_srcdir)/lib/libspl/include/sys/sunddi.h \
 	$(top_srcdir)/lib/libspl/include/sys/systeminfo.h \
 	$(top_srcdir)/lib/libspl/include/sys/time.h \
-	$(top_srcdir)/lib/libspl/include/sys/trace_defs.h \
+	$(top_srcdir)/lib/libspl/include/sys/trace_spl.h \
+	$(top_srcdir)/lib/libspl/include/sys/trace_zfs.h \
 	$(top_srcdir)/lib/libspl/include/sys/types32.h \
 	$(top_srcdir)/lib/libspl/include/sys/types.h \
 	$(top_srcdir)/lib/libspl/include/sys/tzfile.h \
diff --git a/lib/libspl/include/sys/trace_spl.h b/lib/libspl/include/sys/trace_spl.h
new file mode 100644
index 000000000..b80d288f7
--- /dev/null
+++ b/lib/libspl/include/sys/trace_spl.h
@@ -0,0 +1,24 @@
+/* Here to keep the libspl build happy */
+
+#ifndef _LIBSPL_SPL_TRACE_H
+#define	_LIBSPL_SPL_TRACE_H
+
+/*
+ * 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).
+ */
+#undef SET_ERROR
+#define	SET_ERROR(err) \
+	(__set_error(__FILE__, __func__, __LINE__, err), err)
+
+
+#endif
diff --git a/lib/libspl/include/sys/trace_defs.h b/lib/libspl/include/sys/trace_zfs.h
index 87ed5ad3c..87ed5ad3c 100644
--- a/lib/libspl/include/sys/trace_defs.h
+++ b/lib/libspl/include/sys/trace_zfs.h