[Qemu-devel] [PATCH] aio-posix: Don't use epoll if epoll_create1 not available

[Qemu-devel] [PATCH] aio-posix: Don't use epoll if epoll_create1 not available

[Fam Zheng]

Reported-by: Matthew Fortune <Matthew.Fortune@imgtec.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 aio-posix.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/aio-posix.c b/aio-posix.c
index fa7f8ab..97e5a0c 100644
--- a/aio-posix.c
+++ b/aio-posix.c
@@ -18,7 +18,9 @@
 #include "block/block.h"
 #include "qemu/queue.h"
 #include "qemu/sockets.h"
-#ifdef CONFIG_EPOLL
+
+#if defined(CONFIG_EPOLL) && defined(CONFIG_EPOLL_CREATE1)
+#define USE_EPOLL 1
 #include <sys/epoll.h>
 #endif
 
@@ -33,7 +35,7 @@ struct AioHandler
     QLIST_ENTRY(AioHandler) node;
 };
 
-#ifdef CONFIG_EPOLL
+#ifdef USE_EPOLL
 
 /* The fd number threashold to switch to epoll */
 #define EPOLL_ENABLE_THRESHOLD 64
@@ -483,7 +485,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
 
 void aio_context_setup(AioContext *ctx, Error **errp)
 {
-#ifdef CONFIG_EPOLL
+#ifdef USE_EPOLL
     assert(!ctx->epollfd);
     ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
     if (ctx->epollfd == -1) {
-- 
2.4.3

Re: [Qemu-devel] [PATCH] aio-posix: Don't use epoll if epoll_create1 not available

[Stefan Hajnoczi]

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On Tue, Feb 23, 2016 at 09:20:14AM +0800, Fam Zheng wrote:
> Reported-by: Matthew Fortune <Matthew.Fortune@imgtec.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  aio-posix.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/aio-posix.c b/aio-posix.c
> index fa7f8ab..97e5a0c 100644
> --- a/aio-posix.c
> +++ b/aio-posix.c
> @@ -18,7 +18,9 @@
>  #include "block/block.h"
>  #include "qemu/queue.h"
>  #include "qemu/sockets.h"
> -#ifdef CONFIG_EPOLL
> +
> +#if defined(CONFIG_EPOLL) && defined(CONFIG_EPOLL_CREATE1)
> +#define USE_EPOLL 1

Other Linux syscalls with multiple versions for CLOEXEC support tend to
be wrapped in util/osdep.c.  When CLOEXEC isn't available they just skip
it rather than manually adding the flag using fcntl(2).

The following function is added:

  int qemu_epoll_create(void)
  {
  #if defined(CONFIG_EPOLL_CREATE1)
      return epoll_create1(EPOLL_CLOEXEC);
  #elif defined(CONFIG_EPOLL)
      return epoll_create(1);
  #else
      return -ENOSYS;
  #endif
  }

Now the rest of QEMU can rely on just CONFIG_EPOLL.

Even if you don't want to add qemu_epoll_create(), please keep things
simple by doing just s/CONFIG_EPOLL/CONFIG_EPOLL_CREATE1/ in
aio-posix.c.  That way USE_EPOLL isn't needed.  It's confusing to have
multiple preprocessor definitions related to epoll.

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