Add event handlers for module load and unload events. The load handlers are

called after the module has been loaded, and the unload handlers are called
before the module is unloaded. Moreover, the module unload handlers may
return an error to prevent the unload from proceeding.

Reviewed by:	avg
MFC after:	2 weeks

3 files changed, 22 insertions, 3 deletions

diff --git a/share/man/man9/EVENTHANDLER.9 b/share/man/man9/EVENTHANDLER.9
index 4a1666087c9b..ee015cd7909e 100644
--- a/share/man/man9/EVENTHANDLER.9
+++ b/share/man/man9/EVENTHANDLER.9
@@ -23,7 +23,7 @@
 .\" SUCH DAMAGE.
 .\" $FreeBSD$
 .\"
-.Dd May 11, 2012
+.Dd August 1, 2013
 .Dt EVENTHANDLER 9
 .Os
 .Sh NAME
@@ -199,6 +199,12 @@ Callbacks invoked when a new network interface appears.
 Callbacks invoked when a network interface is taken down.
 .It Vt bpf_track
 Callbacks invoked when a BPF listener attaches to/detaches from network interface.
+.It Vt mod_load
+Callbacks invoked after a module has been loaded.
+.It Vt mod_unload
+Callbacks invoked before a module is about to be unloaded.
+These callbacks may be used to return an error and prevent the unload from
+proceeding.
 .It Vt power_profile_change
 Callbacks invoked when the power profile of the system changes.
 .It Vt process_exec
diff --git a/sys/kern/kern_linker.c b/sys/kern/kern_linker.c
index b3ab4df35a27..883752b613d1 100644
--- a/sys/kern/kern_linker.c
+++ b/sys/kern/kern_linker.c
@@ -45,6 +45,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/module.h>
 #include <sys/mount.h>
 #include <sys/linker.h>
+#include <sys/eventhandler.h>
 #include <sys/fcntl.h>
 #include <sys/jail.h>
 #include <sys/libkern.h>
@@ -1046,6 +1047,9 @@ kern_kldload(struct thread *td, const char *file, int *fileid)
 	lf->userrefs++;
 	if (fileid != NULL)
 		*fileid = lf->id;
+
+	EVENTHANDLER_INVOKE(mod_load, lf);
+
 #ifdef HWPMC_HOOKS
 	KLD_DOWNGRADE();
 	pkm.pm_file = lf->filename;
@@ -1101,8 +1105,10 @@ kern_kldunload(struct thread *td, int fileid, int flags)
 	if (lf) {
 		KLD_DPF(FILE, ("kldunload: lf->userrefs=%d\n", lf->userrefs));
 
-		/* Check if there are DTrace probes enabled on this file. */
-		if (lf->nenabled > 0) {
+		EVENTHANDLER_INVOKE(mod_unload, lf, &error);
+		if (error != 0)
+			error = EBUSY;
+		else if (lf->nenabled > 0) {
 			printf("kldunload: attempt to unload file that has"
 			    " DTrace probes enabled\n");
 			error = EBUSY;
diff --git a/sys/sys/eventhandler.h b/sys/sys/eventhandler.h
index 02fbeaa816d1..7e1eee2ecd00 100644
--- a/sys/sys/eventhandler.h
+++ b/sys/sys/eventhandler.h
@@ -266,4 +266,11 @@ EVENTHANDLER_DECLARE(nmbclusters_change, uma_zone_chfn);
 EVENTHANDLER_DECLARE(nmbufs_change, uma_zone_chfn);
 EVENTHANDLER_DECLARE(maxsockets_change, uma_zone_chfn);
 
+/* Module load and unload events */
+struct linker_file;
+typedef void (*mod_load_fn)(void *, struct linker_file *);
+typedef void (*mod_unload_fn)(void *, struct linker_file *, int *);
+EVENTHANDLER_DECLARE(mod_load, mod_load_fn);
+EVENTHANDLER_DECLARE(mod_unload, mod_unload_fn);
+
 #endif /* SYS_EVENTHANDLER_H */