block/curl: check error return of curl_global_init()

If curl_global_init() fails, per the documentation no other curl
functions may be called, so make sure to check the return value.

Also, some minor changes to the initialization latch variable 'inited':

- Make it static in the file, for clarity
- Change the name for clarity
- Make it a bool

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>

block/curl.c

@@ -89,6 +89,8 @@ static CURLMcode __curl_multi_socket_action(CURLM *multi_handle,
 
 struct BDRVCURLState;
 
+static bool libcurl_initialized;
+
 typedef struct CURLAIOCB {
     Coroutine *co;
     QEMUIOVector *qiov;
@@ -686,14 +688,23 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
     double d;
     const char *secretid;
     const char *protocol_delimiter;
+    int ret;
 
-    static int inited = 0;
 
     if (flags & BDRV_O_RDWR) {
         error_setg(errp, "curl block device does not support writes");
         return -EROFS;
     }
 
+    if (!libcurl_initialized) {
+        ret = curl_global_init(CURL_GLOBAL_ALL);
+        if (ret) {
+            error_setg(errp, "libcurl initialization failed with %d", ret);
+            return -EIO;
+        }
+        libcurl_initialized = true;
+    }
+
     qemu_mutex_init(&s->mutex);
     opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
     qemu_opts_absorb_qdict(opts, options, &local_err);
@@ -772,11 +783,6 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
         }
     }
 
-    if (!inited) {
-        curl_global_init(CURL_GLOBAL_ALL);
-        inited = 1;
-    }
-
     DPRINTF("CURL: Opening %s\n", file);
     QSIMPLEQ_INIT(&s->free_state_waitq);
     s->aio_context = bdrv_get_aio_context(bs);