From: Dmitry V. Levin <ldv@altlinux.org>
Date: Wed, 19 Jul 2017 00:33:56 +0000 (+0000)
Subject: userfaultfd: enhance decoding of struct uffdio_api.features
X-Git-Tag: v4.19~249
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=16eded4c4b53d9ac4fa90860f05abeb96855185a;p=strace

userfaultfd: enhance decoding of struct uffdio_api.features

As struct uffdio_api.features has read-write semantics,
print the value returned by the kernel only when it differs
from the value passed to the kernel.

* userfaultfd.c (uffdio_ioctl) <UFFDIO_API>: On entering syscall,
save the value of struct uffdio_api.features.  On exiting syscall, do
not print struct uffdio_api.features when it's the same as on entering.
* tests/ioctl_uffdio.c (main): Update expected output.
---

diff --git a/tests/ioctl_uffdio.c b/tests/ioctl_uffdio.c
index a4115c55..24c642a7 100644
--- a/tests/ioctl_uffdio.c
+++ b/tests/ioctl_uffdio.c
@@ -70,10 +70,12 @@ main(void)
 	api_struct->api = UFFD_API;
 	api_struct->features = 0;
 	rc = ioctl(fd, UFFDIO_API, api_struct);
-	printf("ioctl(%d, UFFDIO_API, {api=0xaa, features=0"
-	       " => features=%#" PRIx64 ", ioctls=1<<_UFFDIO_REGISTER|"
-	       "1<<_UFFDIO_UNREGISTER|1<<_UFFDIO_API",
-	       fd, (uint64_t)api_struct->features);
+	printf("ioctl(%d, UFFDIO_API, {api=0xaa, features=0", fd);
+	if (api_struct->features)
+		printf(" => features=%#" PRIx64,
+		       (uint64_t) api_struct->features);
+	printf(", ioctls=1<<_UFFDIO_REGISTER|"
+	       "1<<_UFFDIO_UNREGISTER|1<<_UFFDIO_API");
 	api_struct->ioctls &= ~(1ull<<_UFFDIO_REGISTER|
 				1ull<<_UFFDIO_UNREGISTER|
 				1ull<<_UFFDIO_API);
diff --git a/userfaultfd.c b/userfaultfd.c
index 41224e2f..07a305b5 100644
--- a/userfaultfd.c
+++ b/userfaultfd.c
@@ -69,6 +69,7 @@ uffdio_ioctl(struct tcb *const tcp, const unsigned int code,
 {
 	switch (code) {
 	case UFFDIO_API: {
+		uint64_t *entering_features;
 		struct uffdio_api ua;
 		if (entering(tcp)) {
 			tprints(", ");
@@ -79,9 +80,18 @@ uffdio_ioctl(struct tcb *const tcp, const unsigned int code,
 			 */
 			PRINT_FIELD_X("{", ua, api);
 			PRINT_FIELD_X(", ", ua, features);
+			entering_features = malloc(sizeof(*entering_features));
+			if (entering_features) {
+				*entering_features = ua.features;
+				set_tcb_priv_data(tcp, entering_features, free);
+			}
 		} else {
 			if (!syserror(tcp) && !umove(tcp, arg, &ua)) {
-				PRINT_FIELD_X(" => ", ua, features);
+				entering_features = get_tcb_priv_data(tcp);
+				if (!entering_features
+				    || *entering_features != ua.features) {
+					PRINT_FIELD_X(" => ", ua, features);
+				}
 				PRINT_FIELD_FLAGS64(", ", ua, ioctls,
 						    uffd_api_flags,
 						    "_UFFDIO_???");