[RFC PATCH 1/9] block/curl: Add an 'offset' parameter, affecting all range requests

[David Edmondson]

A new 'offset' parameter affects all range requests that are sent to
the remote server. The value, in bytes, is simply added to any byte
offset values passed in to the driver.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
---
 block/curl.c                          | 12 +++++++++++-
 docs/system/device-url-syntax.rst.inc |  4 ++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/block/curl.c b/block/curl.c
index 4f907c47be..32ec760f66 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -74,6 +74,7 @@ static CURLMcode __curl_multi_socket_action(CURLM 
*multi_handle,
 #define CURL_BLOCK_OPT_PASSWORD_SECRET "password-secret"
 #define CURL_BLOCK_OPT_PROXY_USERNAME "proxy-username"
 #define CURL_BLOCK_OPT_PROXY_PASSWORD_SECRET "proxy-password-secret"
+#define CURL_BLOCK_OPT_OFFSET "offset"
 
 #define CURL_BLOCK_OPT_READAHEAD_DEFAULT (256 * 1024)
 #define CURL_BLOCK_OPT_SSLVERIFY_DEFAULT true
@@ -135,6 +136,7 @@ typedef struct BDRVCURLState {
     char *password;
     char *proxyusername;
     char *proxypassword;
+    size_t offset;
 } BDRVCURLState;
 
 static void curl_clean_state(CURLState *s);
@@ -658,6 +660,11 @@ static QemuOptsList runtime_opts = {
             .type = QEMU_OPT_STRING,
             .help = "ID of secret used as password for HTTP proxy auth",
         },
+        {
+            .name = CURL_BLOCK_OPT_OFFSET,
+            .type = QEMU_OPT_SIZE,
+            .help = "Offset into underlying content"
+        },
         { /* end of list */ }
     },
 };
@@ -769,6 +776,8 @@ static int curl_open(BlockDriverState *bs, QDict *options, 
int flags,
         }
     }
 
+    s->offset = qemu_opt_get_size(opts, CURL_BLOCK_OPT_OFFSET, 0);
+
     trace_curl_open(file);
     qemu_co_queue_init(&s->free_state_waitq);
     s->aio_context = bdrv_get_aio_context(bs);
@@ -899,7 +908,8 @@ static void curl_setup_preadv(BlockDriverState *bs, 
CURLAIOCB *acb)
     }
     state->acb[0] = acb;
 
-    snprintf(state->range, 127, "%" PRIu64 "-%" PRIu64, start, end);
+    snprintf(state->range, 127, "%" PRIu64 "-%" PRIu64,
+             s->offset + start, s->offset + end);
     trace_curl_setup_preadv(acb->bytes, start, state->range);
     curl_easy_setopt(state->curl, CURLOPT_RANGE, state->range);
 
diff --git a/docs/system/device-url-syntax.rst.inc 
b/docs/system/device-url-syntax.rst.inc
index 88d7a372a7..33f1ddfe6d 100644
--- a/docs/system/device-url-syntax.rst.inc
+++ b/docs/system/device-url-syntax.rst.inc
@@ -197,6 +197,10 @@ These are specified using a special URL syntax.
       get the size of the image to be downloaded. If not set, the
       default timeout of 5 seconds is used.
 
+   ``offset``
+      Add an offset, in bytes, to all range requests sent to the
+      remote server.
+
    Note that when passing options to qemu explicitly, ``driver`` is the
    value of <protocol>.
 
-- 
2.27.0