Patchwork [6/8] enable event_notifier to use pipes

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Submitter Paolo Bonzini
Date May 26, 2010, 2:09 p.m.
Message ID <1274882978-9875-7-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/53619/
State New
Headers show

Comments

Paolo Bonzini - May 26, 2010, 2:09 p.m.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 event_notifier.c |   69 +++++++++++++++++++++++++++++++++++++++---------------
 event_notifier.h |    3 +-
 2 files changed, 52 insertions(+), 20 deletions(-)
Richard Henderson - May 26, 2010, 6:19 p.m.
On 05/26/2010 07:09 AM, Paolo Bonzini wrote:
> -#ifdef CONFIG_EVENTFD
> -#include <sys/eventfd.h>
> -#endif

Is there a reason not to use eventfd if it is available?


r~
Paolo Bonzini - May 26, 2010, 7:48 p.m.
On 05/26/2010 08:19 PM, Richard Henderson wrote:
> On 05/26/2010 07:09 AM, Paolo Bonzini wrote:
>> -#ifdef CONFIG_EVENTFD
>> -#include<sys/eventfd.h>
>> -#endif
>
> Is there a reason not to use eventfd if it is available?

qemu_eventfd chooses between eventfd or pipes.  The reads and writes are 
done so that both cases are accomodated.

Paolo

Patch

diff --git a/event_notifier.c b/event_notifier.c
index 066adb9..a33f3c5 100644
--- a/event_notifier.c
+++ b/event_notifier.c
@@ -10,51 +10,82 @@ 
  * the COPYING file in the top-level directory.
  */
 
+#include "qemu-common.h"
 #include "event_notifier.h"
 #include "qemu-char.h"
-#ifdef CONFIG_EVENTFD
-#include <sys/eventfd.h>
-#endif
 
 int event_notifier_init(EventNotifier *e, int active)
 {
-#ifdef CONFIG_EVENTFD
-    int fd = eventfd(!!active, EFD_NONBLOCK | EFD_CLOEXEC);
-    if (fd < 0)
+    int fds[2];
+    int err;
+    if (qemu_eventfd (fds) < 0)
         return -errno;
-    e->fd = fd;
+
+    err = fcntl_setfl(fds[0], O_NONBLOCK);
+    if (err < 0)
+        goto fail;
+
+    err = fcntl_setfl(fds[1], O_NONBLOCK);
+    if (err < 0)
+        goto fail;
+
+    e->rfd = fds[0];
+    e->wfd = fds[1];
+    if (active)
+        event_notifier_set(e);
     return 0;
-#else
-    return -ENOSYS;
-#endif
+
+fail:
+    close(fds[0]);
+    close(fds[1]);
+    return err;
 }
 
 void event_notifier_cleanup(EventNotifier *e)
 {
-    close(e->fd);
+    close(e->rfd);
+    close(e->wfd);
 }
 
 int event_notifier_get_fd(EventNotifier *e)
 {
-    return e->fd;
+    return e->wfd;
 }
 
 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 f6ec9ef..ff9d6f2 100644
--- a/event_notifier.h
+++ b/event_notifier.h
@@ -4,7 +4,8 @@ 
 #include "qemu-common.h"
 
 struct EventNotifier {
-	int fd;
+    int rfd;
+    int wfd;
 };
 
 typedef void EventNotifierHandler(EventNotifier *);