signalfd compatibility

Port qemu-kvm's signalfd compat code.

commit 5a7fdd0abd7cd24dac205317a4195446ab8748b5
Author: Anthony Liguori <aliguori@us.ibm.com>
Date:   Wed May 7 11:55:47 2008 -0500

    Use signalfd() in io-thread

    This patch reworks the IO thread to use signalfd() instead of sigtimedwait()
    This will eliminate the need to use SIGIO everywhere.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/compatfd.h b/compatfd.h
new file mode 100644
index 0000000..fc37915
--- /dev/null
+++ b/compatfd.h
@@ -0,0 +1,43 @@
+/*
+ * signalfd/eventfd compatibility
+ *
+ * Copyright IBM, Corp. 2008
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_COMPATFD_H
+#define QEMU_COMPATFD_H
+
+#include <signal.h>
+
+struct qemu_signalfd_siginfo {
+    uint32_t ssi_signo;   /* Signal number */
+    int32_t  ssi_errno;   /* Error number (unused) */
+    int32_t  ssi_code;    /* Signal code */
+    uint32_t ssi_pid;     /* PID of sender */
+    uint32_t ssi_uid;     /* Real UID of sender */
+    int32_t  ssi_fd;      /* File descriptor (SIGIO) */
+    uint32_t ssi_tid;     /* Kernel timer ID (POSIX timers) */
+    uint32_t ssi_band;    /* Band event (SIGIO) */
+    uint32_t ssi_overrun; /* POSIX timer overrun count */
+    uint32_t ssi_trapno;  /* Trap number that caused signal */
+    int32_t  ssi_status;  /* Exit status or signal (SIGCHLD) */
+    int32_t  ssi_int;     /* Integer sent by sigqueue(2) */
+    uint64_t ssi_ptr;     /* Pointer sent by sigqueue(2) */
+    uint64_t ssi_utime;   /* User CPU time consumed (SIGCHLD) */
+    uint64_t ssi_stime;   /* System CPU time consumed (SIGCHLD) */
+    uint64_t ssi_addr;    /* Address that generated signal
+                             (for hardware-generated signals) */
+    uint8_t  pad[48];     /* Pad size to 128 bytes (allow for
+                             additional fields in the future) */
+};
+
+int qemu_signalfd(const sigset_t *mask);
+
+#endif