[PATCH v14 05/13] qapi: create BlockdevOptionsCor structure for COR driver

[Vladimir Sementsov-Ogievskiy]

From: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>

Create the BlockdevOptionsCor structure for COR driver specific options
splitting it off form the BlockdevOptionsGenericFormat. The only option
'bottom' node in the structure denotes an image file that limits the
COR operations in the backing chain.
We are going to use the COR-filter for a block-stream job and will pass
a bottom node name to the COR driver. The bottom node is the first
non-filter overlay of the base. It was introduced because the base node
itself may change due to possible concurrent jobs.

Suggested-by: Max Reitz <mreitz@redhat.com>
Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
  [vsementsov: fix bdrv_is_allocated_above() usage]
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qapi/block-core.json | 21 +++++++++++++++-
 block/copy-on-read.c | 57 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 8ef3df6767..04055ef50c 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3942,6 +3942,25 @@
   'data': { 'throttle-group': 'str',
             'file' : 'BlockdevRef'
              } }
+
+##
+# @BlockdevOptionsCor:
+#
+# Driver specific block device options for the copy-on-read driver.
+#
+# @bottom: the name of a non-filter node (allocation-bearing layer) that limits
+#          the COR operations in the backing chain (inclusive).
+#          For the block-stream job, it will be the first non-filter overlay of
+#          the base node. We do not involve the base node into the COR
+#          operations because the base may change due to a concurrent
+#          block-commit job on the same backing chain.
+#
+# Since: 5.2
+##
+{ 'struct': 'BlockdevOptionsCor',
+  'base': 'BlockdevOptionsGenericFormat',
+  'data': { '*bottom': 'str' } }
+
 ##
 # @BlockdevOptions:
 #
@@ -3994,7 +4013,7 @@
       'bochs':      'BlockdevOptionsGenericFormat',
       'cloop':      'BlockdevOptionsGenericFormat',
       'compress':   'BlockdevOptionsGenericFormat',
-      'copy-on-read':'BlockdevOptionsGenericFormat',
+      'copy-on-read':'BlockdevOptionsCor',
       'dmg':        'BlockdevOptionsGenericFormat',
       'file':       'BlockdevOptionsFile',
       'ftp':        'BlockdevOptionsCurlFtp',
diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index 618c4c4f43..67f61983c0 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -24,18 +24,23 @@
 #include "block/block_int.h"
 #include "qemu/module.h"
 #include "qapi/error.h"
+#include "qapi/qmp/qdict.h"
 #include "block/copy-on-read.h"
 
 
 typedef struct BDRVStateCOR {
     bool active;
+    BlockDriverState *bottom_bs;
 } BDRVStateCOR;
 
 
 static int cor_open(BlockDriverState *bs, QDict *options, int flags,
                     Error **errp)
 {
+    BlockDriverState *bottom_bs = NULL;
     BDRVStateCOR *state = bs->opaque;
+    /* Find a bottom node name, if any */
+    const char *bottom_node = qdict_get_try_str(options, "bottom");
 
     bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
                                BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
@@ -51,7 +56,17 @@ static int cor_open(BlockDriverState *bs, QDict *options, 
int flags,
         ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
             bs->file->bs->supported_zero_flags);
 
+    if (bottom_node) {
+        bottom_bs = bdrv_lookup_bs(NULL, bottom_node, errp);
+        if (!bottom_bs) {
+            error_setg(errp, "Bottom node '%s' not found", bottom_node);
+            qdict_del(options, "bottom");
+            return -EINVAL;
+        }
+        qdict_del(options, "bottom");
+    }
     state->active = true;
+    state->bottom_bs = bottom_bs;
 
     /*
      * We don't need to call bdrv_child_refresh_perms() now as the permissions
@@ -107,8 +122,46 @@ static int coroutine_fn 
cor_co_preadv_part(BlockDriverState *bs,
                                            size_t qiov_offset,
                                            int flags)
 {
-    return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
-                               flags | BDRV_REQ_COPY_ON_READ);
+    int64_t n;
+    int local_flags;
+    int ret;
+    BDRVStateCOR *state = bs->opaque;
+
+    if (!state->bottom_bs) {
+        return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
+                                   flags | BDRV_REQ_COPY_ON_READ);
+    }
+
+    while (bytes) {
+        local_flags = flags;
+
+        /* In case of failure, try to copy-on-read anyway */
+        ret = bdrv_is_allocated(bs->file->bs, offset, bytes, &n);
+        if (ret <= 0) {
+            ret = 
bdrv_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
+                                          state->bottom_bs, true, offset,
+                                          n, &n);
+            if (ret > 0 || ret < 0) {
+                local_flags |= BDRV_REQ_COPY_ON_READ;
+            }
+            /* Finish earlier if the end of a backing file has been reached */
+            if (n == 0) {
+                break;
+            }
+        }
+
+        ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
+                                  local_flags);
+        if (ret < 0) {
+            return ret;
+        }
+
+        offset += n;
+        qiov_offset += n;
+        bytes -= n;
+    }
+
+    return 0;
 }
 
 
-- 
2.21.3