commit bf1915b6d85d3c222200ef5d5fd7745ed299b17b
author Steven Moreland <smoreland@google.com> Thu Jul 16 22:43:02 2020 +0000
committer Steven Moreland <smoreland@google.com> Fri Jul 17 21:42:35 2020 +0000
tree 73713917dda312caa5228d6d0674d104d804f590
parent ea8305102a6cdd1b2cf89b1f020391bd19f71244

libbinder: setMinSchedulerPolicy

This function on BBinder allows the minimum scheduling priority for
incoming binder transactions to be set by the binder driver. This
functionality was originally developed for libhwbinder and ported here.
The main difference from libhwbider is that invalid priority sets cause
an abort, whereas for libhwbinder, an error is returned. Unfortunately,
that error is frequently ignored, and since this reflects static
configuration, abort is considered a benefit.

Bug: 149933095
Test: binderLibTest
Change-Id: Ie93aebb09f4142cd66d841ca8b3ca39d1e0bb75e

libs/binder/Parcel.cpp

diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index 660b96a..c7cb495 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -20,6 +20,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
+#include <linux/sched.h>
 #include <pthread.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -188,16 +189,18 @@
     return OK;
 }
 
+static constexpr inline int schedPolicyMask(int policy, int priority) {
+    return (priority & FLAT_BINDER_FLAG_PRIORITY_MASK) | ((policy & 3) << FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT);
+}
+
 status_t Parcel::flattenBinder(const sp<IBinder>& binder)
 {
     flat_binder_object obj;
+    obj.flags = FLAT_BINDER_FLAG_ACCEPTS_FDS;
 
-    if (IPCThreadState::self()->backgroundSchedulingDisabled()) {
-        /* minimum priority for all nodes is nice 0 */
-        obj.flags = FLAT_BINDER_FLAG_ACCEPTS_FDS;
-    } else {
-        /* minimum priority for all nodes is MAX_NICE(19) */
-        obj.flags = 0x13 | FLAT_BINDER_FLAG_ACCEPTS_FDS;
+    int schedBits = 0;
+    if (!IPCThreadState::self()->backgroundSchedulingDisabled()) {
+        schedBits = schedPolicyMask(SCHED_NORMAL, 19);
     }
 
     if (binder != nullptr) {
@@ -213,6 +216,13 @@
             obj.handle = handle;
             obj.cookie = 0;
         } else {
+            int policy = local->getMinSchedulerPolicy();
+            int priority = local->getMinSchedulerPriority();
+
+            if (policy != 0 || priority != 0) {
+                // override value, since it is set explicitly
+                schedBits = schedPolicyMask(policy, priority);
+            }
             if (local->isRequestingSid()) {
                 obj.flags |= FLAT_BINDER_FLAG_TXN_SECURITY_CTX;
             }
@@ -226,6 +236,8 @@
         obj.cookie = 0;
     }
 
+    obj.flags |= schedBits;
+
     return finishFlattenBinder(binder, obj);
 }