[Qemu-devel] [PATCH 02/17] event_notifier: enable it to use pipes

[Paolo Bonzini <pbonzini@redhat.com>]

This takes the eventfd emulation code from the main loop.  When the
EventNotifier is used for the main loop too, we need this compatibility
code.

Without CONFIG_EVENTFD, event_notifier_get_fd is only usable for the
"read" side of the notifier, for example to set a select() handler.

Reviewed-by: Anthony Liguori <anthony@codemonkey.ws>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 event_notifier.c | 83 +++++++++++++++++++++++++++++++++++++++++++++-----------
 event_notifier.h |  3 +-
 2 file modificati, 69 inserzioni(+), 17 rimozioni(-)

diff --git a/event_notifier.c b/event_notifier.c
index 2c207e1..88c114b 100644
--- a/event_notifier.c
+++ b/event_notifier.c
@@ -20,48 +20,99 @@
 
 void event_notifier_init_fd(EventNotifier *e, int fd)
 {
-    e->fd = fd;
+    e->rfd = fd;
+    e->wfd = fd;
 }
 
 int event_notifier_init(EventNotifier *e, int active)
 {
+    int fds[2];
+    int ret;
+
 #ifdef CONFIG_EVENTFD
-    int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);
-    if (fd < 0)
-        return -errno;
-    e->fd = fd;
-    return 0;
+    ret = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
 #else
-    return -ENOSYS;
+    ret = -1;
+    errno = ENOSYS;
 #endif
+    if (ret >= 0) {
+        e->rfd = e->wfd = ret;
+    } else {
+        if (errno != ENOSYS) {
+            return -errno;
+        }
+        if (qemu_pipe(fds) < 0) {
+            return -errno;
+        }
+        ret = fcntl_setfl(fds[0], O_NONBLOCK);
+        if (ret < 0) {
+            goto fail;
+        }
+        ret = fcntl_setfl(fds[1], O_NONBLOCK);
+        if (ret < 0) {
+            goto fail;
+        }
+        e->rfd = fds[0];
+        e->wfd = fds[1];
+    }
+    if (active) {
+        event_notifier_set(e);
+    }
+    return 0;
+
+fail:
+    close(fds[0]);
+    close(fds[1]);
+    return ret;
 }
 
 void event_notifier_cleanup(EventNotifier *e)
 {
-    close(e->fd);
+    if (e->rfd != e->wfd) {
+        close(e->rfd);
+    }
+    close(e->wfd);
 }
 
 int event_notifier_get_fd(EventNotifier *e)
 {
-    return e->fd;
+    return e->rfd;
 }
 
 int event_notifier_set_handler(EventNotifier *e,
                                EventNotifierHandler *handler)
 {
-    return qemu_set_fd_handler(e->fd, (IOHandler *)handler, NULL, e);
+    return qemu_set_fd_handler(e->rfd, (IOHandler *)handler, NULL, e);
 }
 
 int event_notifier_set(EventNotifier *e)
 {
-    uint64_t value = 1;
-    int r = write(e->fd, &value, sizeof(value));
-    return r == sizeof(value);
+    static const uint64_t value = 1;
+    ssize_t ret;
+
+    do {
+        ret = write(e->wfd, &value, sizeof(value));
+    } while (ret < 0 && errno == EINTR);
+
+    /* EAGAIN is fine, a read must be pending.  */
+    if (ret < 0 && errno != EAGAIN) {
+        return -1;
+    }
+    return 0;
 }
 
 int event_notifier_test_and_clear(EventNotifier *e)
 {
-    uint64_t value;
-    int r = read(e->fd, &value, sizeof(value));
-    return r == sizeof(value);
+    int value;
+    ssize_t len;
+    char buffer[512];
+
+    /* Drain the notify pipe.  For eventfd, only 8 bytes will be read.  */
+    value = 0;
+    do {
+        len = read(e->rfd, buffer, sizeof(buffer));
+        value |= (len > 0);
+    } while ((len == -1 && errno == EINTR) || len == sizeof(buffer));
+
+    return value;
 }
diff --git a/event_notifier.h b/event_notifier.h
index f0ec2f2..f04d12d 100644
--- a/event_notifier.h
+++ b/event_notifier.h
@@ -16,7 +16,8 @@
 #include "qemu-common.h"
 
 struct EventNotifier {
-    int fd;
+    int rfd;
+    int wfd;
 };
 
 typedef void EventNotifierHandler(EventNotifier *);
-- 
1.7.12