Patchwork [02/17] event_notifier: enable it to use pipes

login
register
mail settings
Submitter Paolo Bonzini
Date Sept. 25, 2012, 12:55 p.m.
Message ID <1348577763-12920-3-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/186805/
State New
Headers show

Comments

Paolo Bonzini - Sept. 25, 2012, 12:55 p.m.
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(-)
Stefan Hajnoczi - Oct. 8, 2012, 7:03 a.m.
On Tue, Sep 25, 2012 at 02:55:48PM +0200, Paolo Bonzini wrote:
>  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) {

ret = -errno;

> +            goto fail;
> +        }
> +        ret = fcntl_setfl(fds[1], O_NONBLOCK);
> +        if (ret < 0) {

ret = -errno;

> +            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;

If we're changing the return value representation, then we might as well:

return -errno;

But no caller actually checks the return value.

Patch

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 *);