libhealthloop: Handle netlink receive buffer overflows

The Linux kernel netlink implementation sets EPOLLERR if delivery of a
netlink message fails because of a buffer overrun (see also the Linux
kernel netlink_overrun() and sock_def_error_report() functions). Handle
buffer overruns by calling ScheduleBatteryUpdate() unconditionally.

Bug: 203462310
Change-Id: I54f7d239e6b4caad0db4d1b15de7c0385f796ebd
Signed-off-by: Bart Van Assche <bvanassche@google.com>

health/utils/libhealthloop/HealthLoop.cpp

@@ -57,14 +57,13 @@ int HealthLoop::RegisterEvent(int fd, BoundFunction func, EventWakeup wakeup) {
                                           EventHandler{this, fd, std::move(func)}))
                                   .get();
 
-    struct epoll_event ev;
-
-    ev.events = EPOLLIN;
+    struct epoll_event ev = {
+            .events = EPOLLIN | EPOLLERR,
+            .data.ptr = reinterpret_cast<void*>(event_handler),
+    };
 
     if (wakeup == EVENT_WAKEUP_FD) ev.events |= EPOLLWAKEUP;
 
-    ev.data.ptr = reinterpret_cast<void*>(event_handler);
-
     if (epoll_ctl(epollfd_, EPOLL_CTL_ADD, fd, &ev) == -1) {
         KLOG_ERROR(LOG_TAG, "epoll_ctl failed; errno=%d\n", errno);
         return -1;
@@ -119,9 +118,15 @@ void HealthLoop::PeriodicChores() {
 
 // TODO(b/140330870): Use BPF instead.
 #define UEVENT_MSG_LEN 2048
-void HealthLoop::UeventEvent(uint32_t /*epevents*/) {
+void HealthLoop::UeventEvent(uint32_t epevents) {
     // No need to lock because uevent_fd_ is guaranteed to be initialized.
 
+    if (epevents & EPOLLERR) {
+        // The netlink receive buffer overflowed.
+        ScheduleBatteryUpdate();
+        return;
+    }
+
     char msg[UEVENT_MSG_LEN + 2];
     char* cp;
     int n;