ioctl: allow to stop decoding number

For some ioctls, like from drm, the identification of the correct ioctl
is done by custom code.  Specifying IOCTL_NUMBER_STOP_LOOKUP on
return of ioctl_decode_command_number() disables further calls to
ioctl_lookup().

* defs.h (IOCTL_NUMBER_UNKNOWN, IOCTL_NUMBER_HANDLED,
IOCTL_NUMBER_STOP_LOOKUP): Add macros representing ioctl number state
decoding.
* ioctl.c (SYS_FUNC(ioctl)): Skip ioctl_lookup() when
ioctl_decode_command_number() returns a value with
IOCTL_NUMBER_STOP_LOOKUP flag is set.

Suggested-by: Patrik Jakobsson <[email protected]>
Signed-off-by: Gabriel Laskar <[email protected]>
Signed-off-by: Dmitry V. Levin <[email protected]>

Author: GabrielL

defs.h

@@ -450,6 +450,10 @@ extern const struct xlat whence_codes[];
 #define STACKTRACE_CAPTURE_ON_ENTER 01000 /* Capture stacktrace on "entering" stage */
 #define TRACE_INDIRECT_SUBCALL	02000	/* Syscall is an indirect socket/ipc subcall. */
 
+#define IOCTL_NUMBER_UNKNOWN 0
+#define IOCTL_NUMBER_HANDLED 1
+#define IOCTL_NUMBER_STOP_LOOKUP 010
+
 #define indirect_ipccall(tcp) (tcp->s_ent->sys_flags & TRACE_INDIRECT_SUBCALL)
 
 #if defined(ARM) || defined(AARCH64) \

ioctl.c

@@ -278,15 +278,17 @@ SYS_FUNC(ioctl)
 		printfd(tcp, tcp->u_arg[0]);
 		tprints(", ");
 		ret = ioctl_decode_command_number(tcp);
-		iop = ioctl_lookup(tcp->u_arg[1]);
-		if (iop) {
-			if (ret)
-				tprints(" or ");
-			tprints(iop->symbol);
-			while ((iop = ioctl_next_match(iop)))
-				tprintf(" or %s", iop->symbol);
-		} else if (!ret) {
-			ioctl_print_code(tcp->u_arg[1]);
+		if (!(ret & IOCTL_NUMBER_STOP_LOOKUP)) {
+			iop = ioctl_lookup(tcp->u_arg[1]);
+			if (iop) {
+				if (ret)
+					tprints(" or ");
+				tprints(iop->symbol);
+				while ((iop = ioctl_next_match(iop)))
+					tprintf(" or %s", iop->symbol);
+			} else if (!ret) {
+				ioctl_print_code(tcp->u_arg[1]);
+			}
 		}
 		ret = ioctl_decode(tcp);
 	} else {