Avoid blocking read from iphb socket

In theory there should be something to read unless it is possible
that glib can call io watch with null condition. Still there is
at least one crash report where dsme process watchdog has killed
mce that was stuck at iphb socket read.

Check validity of io watch id, add explicit test for G_IO_IN and
use nonblocking recv() instead of vanilla read().

[mce] Avoid blocking read from iphb socket. Fixes JB#28990

mce-hbtimer.c

@@ -33,6 +33,9 @@
 # include "libwakelock.h"
 #endif
 
+#include <sys/types.h>
+#include <sys/socket.h>
+
 #include <stdlib.h>
 #include <stdint.h>
 #include <inttypes.h>
@@ -703,6 +706,9 @@ mht_iphb_wakeup_cb(GIOChannel *chn, GIOCondition cnd, gpointer data)
 
     gboolean keep_going = FALSE;
 
+    if( !mht_iphb_wakeup_watch_id )
+        goto cleanup_nak;
+
     int fd = g_io_channel_unix_get_fd(chn);
 
     if( fd < 0 )
@@ -711,9 +717,12 @@ mht_iphb_wakeup_cb(GIOChannel *chn, GIOCondition cnd, gpointer data)
     if( cnd & ~G_IO_IN )
         goto cleanup_nak;
 
+    if( !(cnd & G_IO_IN) )
+        goto cleanup_ack;
+
     char buf[256];
 
-    int rc = read(fd, buf, sizeof buf);
+    int rc = recv(fd, buf, sizeof buf, MSG_DONTWAIT);
 
     if( rc == 0 ) {
         if( !shutting_down )
@@ -722,7 +731,7 @@ mht_iphb_wakeup_cb(GIOChannel *chn, GIOCondition cnd, gpointer data)
     }
 
     if( rc == -1 ) {
-        if( errno == EINTR || errno == EAGAIN )
+        if( errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK )
             goto cleanup_ack;
 
         mce_log(LL_ERR, "read error: %m");