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>

compatfd.c

@@ -0,0 +1,117 @@
+/*
+ * 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.
+ *
+ */
+
+#include "qemu-common.h"
+#include "compatfd.h"
+
+#include <sys/syscall.h>
+#include <pthread.h>
+
+struct sigfd_compat_info
+{
+    sigset_t mask;
+    int fd;
+};
+
+static void *sigwait_compat(void *opaque)
+{
+    struct sigfd_compat_info *info = opaque;
+    int err;
+    sigset_t all;
+
+    sigfillset(&all);
+    sigprocmask(SIG_BLOCK, &all, NULL);
+
+    do {
+        siginfo_t siginfo;
+
+        err = sigwaitinfo(&info->mask, &siginfo);
+        if (err == -1 && errno == EINTR) {
+            err = 0;
+            continue;
+        }
+
+        if (err > 0) {
+            char buffer[128];
+            size_t offset = 0;
+
+            memcpy(buffer, &err, sizeof(err));
+            while (offset < sizeof(buffer)) {
+                ssize_t len;
+
+                len = write(info->fd, buffer + offset,
+                            sizeof(buffer) - offset);
+                if (len == -1 && errno == EINTR)
+                    continue;
+
+                if (len <= 0) {
+                    err = -1;
+                    break;
+                }
+
+                offset += len;
+            }
+        }
+    } while (err >= 0);
+
+    return NULL;
+}
+
+static int qemu_signalfd_compat(const sigset_t *mask)
+{
+    pthread_attr_t attr;
+    pthread_t tid;
+    struct sigfd_compat_info *info;
+    int fds[2];
+
+    info = malloc(sizeof(*info));
+    if (info == NULL) {
+        errno = ENOMEM;
+        return -1;
+    }
+
+    if (pipe(fds) == -1) {
+        free(info);
+        return -1;
+    }
+
+    qemu_set_cloexec(fds[0]);
+    qemu_set_cloexec(fds[1]);
+
+    memcpy(&info->mask, mask, sizeof(*mask));
+    info->fd = fds[1];
+
+    pthread_attr_init(&attr);
+    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+
+    pthread_create(&tid, &attr, sigwait_compat, info);
+
+    pthread_attr_destroy(&attr);
+
+    return fds[0];
+}
+
+int qemu_signalfd(const sigset_t *mask)
+{
+#if defined(CONFIG_SIGNALFD)
+    int ret;
+
+    ret = syscall(SYS_signalfd, -1, mask, _NSIG / 8);
+    if (ret != -1) {
+        qemu_set_cloexec(ret);
+        return ret;
+    }
+#endif
+
+    return qemu_signalfd_compat(mask);
+}