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Re: [PATCH v11 04/13] copy-on-read: pass overlay base node name to COR d

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v11 04/13] copy-on-read: pass overlay base node name to COR driver
Date: Wed, 14 Oct 2020 17:56:15 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.2

14.10.2020 14:57, Max Reitz wrote:
On 14.10.20 13:09, Max Reitz wrote:
On 12.10.20 19:43, Andrey Shinkevich wrote:
We are going to use the COR-filter for a block-stream job.
To limit COR operations by the base node in the backing chain during
stream job, pass the name of overlay base node to the copy-on-read
driver as base node itself may change due to possible concurrent jobs.
The rest of the functionality will be implemented in the patch that

Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
  block/copy-on-read.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)

Is there a reason why you didn’t add this option to QAPI (as part of a
yet-to-be-created BlockdevOptionsCor)?  Because I’d really like it there.

diff --git a/block/copy-on-read.c b/block/copy-on-read.c
index bcccf0f..c578b1b 100644
--- a/block/copy-on-read.c
+++ b/block/copy-on-read.c
@@ -24,19 +24,24 @@
  #include "block/block_int.h"
  #include "qemu/module.h"
  #include "qapi/error.h"
+#include "qapi/qmp/qerror.h"
  #include "qapi/qmp/qdict.h"
  #include "block/copy-on-read.h"
typedef struct BDRVStateCOR {
      bool active;
+    BlockDriverState *base_overlay;
  } BDRVStateCOR;
static int cor_open(BlockDriverState *bs, QDict *options, int flags,
                      Error **errp)
+    BlockDriverState *base_overlay = NULL;
      BDRVStateCOR *state = bs->opaque;
+    /* We need the base overlay node rather than the base itself */
+    const char *base_overlay_node = qdict_get_try_str(options, "base");

Shouldn’t it be called base-overlay or above-base then?

While reviewing patch 5, I realized this sould indeed be base-overlay
(i.e. the next allocation-bearing layer above the base, not just a
filter on top of base), but that should be noted somewhere, of course.
Best would be the QAPI documentation for this option. O:)

What about naming it just "bottom" or "bottom-node"? If we don't have base, it's strange to have something 
"relative to base". And we can document, that "bottom" must be a non-filter node in a backing chain of 

Best regards,

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