Add ability to proxy ioprio of client apps (#1534)

src/ioprio.cpp

@@ -0,0 +1,73 @@
+#include "ioprio.hpp"
+
+#ifdef __linux__
+# include <linux/ioprio.h>
+# include <sys/syscall.h>
+# include <unistd.h>
+# include <errno.h>
+#else
+#warning "ioprio not supported on this platform"
+#endif
+
+thread_local int ioprio::SetFrom::thread_prio = -1;
+bool _enabled = false;
+
+int
+ioprio::get(const int which_,
+            const int who_)
+{
+#ifdef SYS_ioprio_get
+  int rv;
+
+  rv = syscall(SYS_ioprio_get,which_,who_);
+
+  return ((rv == -1) ? -errno : rv);
+#else
+  return -ENOSUP;
+#endif
+}
+
+int
+ioprio::set(const int which_,
+            const int who_,
+            const int ioprio_)
+{
+#ifdef SYS_ioprio_set
+  int rv;
+
+  rv = syscall(SYS_ioprio_set,which_,who_,ioprio_);
+
+  return ((rv == -1) ? -errno : rv);
+#else
+  return -ENOSUP;
+#endif
+}
+
+void
+ioprio::enable(const bool enable_)
+{
+  _enabled = enable_;
+}
+
+bool
+ioprio::enabled()
+{
+  return _enabled;
+}
+
+ioprio::SetFrom::SetFrom(const pid_t pid_)
+{
+  int client_prio;
+
+  if(!_enabled)
+    return;
+
+  client_prio = ioprio::get(IOPRIO_WHO_PROCESS,pid_);
+  if(client_prio < 0)
+    return;
+  if(client_prio == thread_prio)
+    return;
+
+  thread_prio = client_prio;
+  ioprio::set(IOPRIO_WHO_PROCESS,0,client_prio);
+}