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Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
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Date: Wed, 15 Jan 2014 23:06:23 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block/curl: Implement the libcurl timer
	callback interface
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Kevin Wolf <kwolf@redhat.com>, patches@linaro.org, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, qemu-stable@nongnu.org

Il 15/01/2014 18:23, Peter Maydell ha scritto:
> libcurl versions 7.16.0 and later have a timer callback interface which
> must be implemented in order for libcurl to make forward progress (it
> will sometimes rely on being called back on the timeout if there are
> no file descriptors registered). Implement the callback, and use a
> QEMU AIO timer to ensure we prod libcurl again when it asks us to.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> This fixes the problem I was seeing where trying to use the curl block
> backend just hung. I'm not sure whether all libcurl versions that provide
> the timer callback API require its use, but it shouldn't hurt.

It still hangs here, but the adding the following patch on top fixes
curl on Fedora for me!

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/block/curl.c b/block/curl.c
index 5238961..e0cf138 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -232,20 +232,10 @@ static int curl_find_buf(BDRVCURLState *s, size_t start, size_t len,
     return FIND_RET_NONE;
 }
 
-static void curl_multi_do(void *arg)
+static void curl_multi_read(BDRVCURLState *s)
 {
-    BDRVCURLState *s = (BDRVCURLState *)arg;
-    int running;
-    int r;
     int msgs_in_queue;
 
-    if (!s->multi)
-        return;
-
-    do {
-        r = curl_multi_socket_all(s->multi, &running);
-    } while(r == CURLM_CALL_MULTI_PERFORM);
-
     /* Try to find done transfers, so we can free the easy
      * handle again. */
     do {
@@ -289,6 +279,37 @@ static void curl_multi_do(void *arg)
     } while(msgs_in_queue);
 }
 
+static void curl_multi_do(void *arg)
+{
+    BDRVCURLState *s = (BDRVCURLState *)arg;
+    int running;
+    int r;
+
+    if (!s->multi) {
+        return;
+    }
+
+    do {
+        r = curl_multi_socket_all(s->multi, &running);
+    } while(r == CURLM_CALL_MULTI_PERFORM);
+
+    curl_multi_read(s);
+}
+
+static void curl_multi_timeout_do(void *arg)
+{
+    BDRVCURLState *s = (BDRVCURLState *)arg;
+    int running;
+
+    if (!s->multi) {
+        return;
+    }
+
+    curl_multi_socket_action(s->multi, CURL_SOCKET_TIMEOUT, 0, &running);
+
+    curl_multi_read(s);
+}
+
 static CURLState *curl_init_state(BDRVCURLState *s)
 {
     CURLState *state = NULL;
@@ -498,7 +519,7 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
 
     aio_timer_init(bdrv_get_aio_context(bs), &s->timer,
                    QEMU_CLOCK_REALTIME, SCALE_NS,
-                   curl_multi_do, s);
+                   curl_multi_timeout_do, s);
 
     // Now we know the file exists and its size, so let's
     // initialize the multi interface!