[RFC PATCH 7/9] block/curl: Allow the user to control the number of cache blocks

[David Edmondson <david.edmondson@oracle.com>]

Rather than using a fixed number, allow the user to specify the number
of cache blocks allocated. This cannot be less than the number of Curl
states and defaults to that value.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
---
 block/curl.c                          | 20 +++++++++++++++++---
 docs/system/device-url-syntax.rst.inc |  4 ++++
 qapi/block-core.json                  |  4 ++++
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/block/curl.c b/block/curl.c
index 0ea9eedebd..27fa77c351 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -75,14 +75,15 @@ static CURLMcode __curl_multi_socket_action(CURLM *multi_handle,
 #define CURL_BLOCK_OPT_PROXY_PASSWORD_SECRET "proxy-password-secret"
 #define CURL_BLOCK_OPT_OFFSET "offset"
 #define CURL_BLOCK_OPT_BLOCKSIZE "blocksize"
+#define CURL_BLOCK_OPT_BLOCKCOUNT "blockcount"
 
 #define CURL_BLOCK_OPT_SSLVERIFY_DEFAULT true
 #define CURL_BLOCK_OPT_TIMEOUT_DEFAULT 5
 /* Must be a non-zero power of 2. */
 #define CURL_BLOCK_OPT_BLOCKSIZE_DEFAULT (256 * 1024)
+/* The defaultnumber of blocks to store in the cache. */
+#define CURL_BLOCK_OPT_BLOCKCOUNT_DEFAULT (CURL_NUM_STATES)
 
-/* The maximum number of blocks to store in the cache. */
-#define CURL_BLOCK_CACHE_MAX_BLOCKS 100
 /* The number of heads in the hash table. */
 #define CURL_BLOCK_CACHE_HASH 37
 
@@ -161,6 +162,7 @@ typedef struct BDRVCURLState {
     char *proxypassword;
     size_t offset;
     size_t blocksize;
+    int cache_max;
     int cache_allocated; /* The number of block_t currently allocated. */
     QLIST_HEAD(, block) cache_free;
     QTAILQ_HEAD(, block) cache_lru;
@@ -287,7 +289,7 @@ static block_t *curl_cache_get(BDRVCURLState *s)
     }
 
     /* If not at the limit, try get a new one. */
-    if (s->cache_allocated < CURL_BLOCK_CACHE_MAX_BLOCKS) {
+    if (s->cache_allocated < s->cache_max) {
         b = curl_cache_alloc(s);
         if (b) {
             b->use++;
@@ -929,6 +931,11 @@ static QemuOptsList runtime_opts = {
             .type = QEMU_OPT_SIZE,
             .help = "Block size for IO requests"
         },
+        {
+            .name = CURL_BLOCK_OPT_BLOCKCOUNT,
+            .type = QEMU_OPT_SIZE,
+            .help = "Maximum number of cached blocks"
+        },
         { /* end of list */ }
     },
 };
@@ -1039,6 +1046,13 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
         error_setg(errp, "blocksize must be a non-zero power of two");
         goto out_noclean;
     }
+    s->cache_max = qemu_opt_get_size(opts, CURL_BLOCK_OPT_BLOCKCOUNT,
+                                     CURL_BLOCK_OPT_BLOCKCOUNT_DEFAULT);
+    if (s->cache_max < CURL_NUM_STATES) {
+        error_setg(errp, "blockcount must be larger than %d",
+            CURL_NUM_STATES - 1);
+        goto out_noclean;
+    }
 
     trace_curl_open(file);
     qemu_co_queue_init(&s->free_state_waitq);
diff --git a/docs/system/device-url-syntax.rst.inc b/docs/system/device-url-syntax.rst.inc
index ee504ee41a..56843cb38f 100644
--- a/docs/system/device-url-syntax.rst.inc
+++ b/docs/system/device-url-syntax.rst.inc
@@ -201,6 +201,10 @@ These are specified using a special URL syntax.
       bytes. The value must be a non-zero power of two.  It defaults
       to 256kB.
 
+   ``blockcount``
+      The number of ``blocksize`` blocks that the system may allocate
+      to store data read from the remote server.
+
    Note that when passing options to qemu explicitly, ``driver`` is the
    value of <protocol>.
 
diff --git a/qapi/block-core.json b/qapi/block-core.json
index cd16197e1e..91888166fa 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3767,11 +3767,15 @@
 # @blocksize: Size of all IO requests sent to the remote server; must
 #             be a non-zero power of two (defaults to 1 256kB)
 #
+# @blockcount: The number of IO blocks used to cache data from the
+#              remote server.
+#
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsCurlBase',
   'data': { 'url': 'str',
             '*blocksize': 'int',
+            '*blockcount': 'int',
             '*timeout': 'int',
             '*username': 'str',
             '*password-secret': 'str',
-- 
2.27.0