[Qemu-devel] [PATCH 3/5] Use qemu_eventfd for POSIX AIO

[Jan Kiszka]

Use qemu_eventfd for signaling POSIX AIO completions. If native eventfd
suport is available, this avoids multiple read accesses to drain
multiple pending signals. As before we use a pipe if eventfd is not
supported.

Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
---
 posix-aio-compat.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/posix-aio-compat.c b/posix-aio-compat.c
index c9b8ebf..7c3ff6e 100644
--- a/posix-aio-compat.c
+++ b/posix-aio-compat.c
@@ -481,7 +481,7 @@ static void posix_aio_read(void *opaque)
     PosixAioState *s = opaque;
     ssize_t len;
 
-    /* read all bytes from signal pipe */
+    /* read all bytes from eventfd or signal pipe */
     for (;;) {
         char bytes[16];
 
@@ -506,10 +506,14 @@ static PosixAioState *posix_aio_state;
 
 static void posix_aio_notify_event(void)
 {
-    char byte = 0;
+    /* Write 8 bytes to be compatible with eventfd.  */
+    static const uint64_t val = 1;
     ssize_t ret;
 
-    ret = write(posix_aio_state->wfd, &byte, sizeof(byte));
+    do {
+        ret = write(posix_aio_state->wfd, &val, sizeof(val));
+    } while (ret < 0 && errno == EINTR);
+
     if (ret < 0 && errno != EAGAIN)
         die("write()");
 }
@@ -623,7 +627,7 @@ int paio_init(void)
     s = g_malloc(sizeof(PosixAioState));
 
     s->first_aio = NULL;
-    if (qemu_pipe(fds) == -1) {
+    if (qemu_eventfd(fds) == -1) {
         fprintf(stderr, "failed to create pipe\n");
         g_free(s);
         return -1;
-- 
1.7.3.4