[PATCH 4/6] Fill fd_info structure only when a decoder requests

[Masatake YAMATO]

This is a minor optimization.

If a ioctl decoder wants to use fd_info as a hint, the
decoder call tell the request to its upper layer via
newly introduced function ioctl_does_expect_fd_info().

* src/ioctl.c (ioctl_does_expect_fd_info): New function.
(SYS_FUNC(ioctl)): Collect fd_info only when
ioctl_does_expect_fd_info() returns true.

Signed-off-by: Masatake YAMATO <yamato at redhat.com>
---
 src/ioctl.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/ioctl.c b/src/ioctl.c
index 72e827d9c..75f2c30b7 100644
--- a/src/ioctl.c
+++ b/src/ioctl.c
@@ -429,6 +429,20 @@ ioctl_decode(struct tcb *tcp)
 	return 0;
 }
 
+/*
+ * If your ioctl decoder needs the extra inforamtion
+ * about a fd for later processing, return true.
+ */
+static bool ioctl_does_expect_fd_info(struct tcb *tcp)
+{
+	const unsigned int code = tcp->u_arg[1];
+	switch (_IOC_TYPE(code)) {
+	case 'T':
+		return true;
+	}
+	return false;
+}
+
 SYS_FUNC(ioctl)
 {
 	const struct_ioctlent *iop;
@@ -437,7 +451,10 @@ SYS_FUNC(ioctl)
 	if (entering(tcp)) {
 		struct fd_info *fd_info = NULL;
 
-		printfd_filling_info(tcp, tcp->u_arg[0], &fd_info);
+		printfd_filling_info(tcp, tcp->u_arg[0],
+				     ioctl_does_expect_fd_info(tcp)
+				     ? &fd_info
+				     : NULL);
 		tprint_arg_next();
 
 		if (xlat_verbosity != XLAT_STYLE_ABBREV)
-- 
2.35.1