[PATCH v2 5/6] Fill finfo structure only when a decoder requests

[Masatake YAMATO]

This is minor optimization.

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

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

Signed-off-by: Masatake YAMATO <yamato at redhat.com>
---
 src/ioctl.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/ioctl.c b/src/ioctl.c
index a839da817..d675c9763 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_finfo(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;
@@ -438,7 +452,8 @@ SYS_FUNC(ioctl)
 		struct finfo finfoa;
 		struct finfo *finfo = NULL;
 		char path[PATH_MAX + 1];
-		if (getfdpath_pid(tcp->pid, tcp->u_arg[0], path, sizeof(path)) >= 0)
+		if (ioctl_does_expect_finfo(tcp)
+		    && getfdpath_pid(tcp->pid, tcp->u_arg[0], path, sizeof(path)) >= 0)
 			finfo = get_finfo_for_dev(path, &finfoa);
 		printfd_with_finfo(tcp, tcp->u_arg[0], finfo);
 		tprint_arg_next();
-- 
2.35.1