14.10.2020 19:08, Andrey Shinkevich wrote:
On 14.10.2020 14:09, 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
follows.
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@xxxxxxxxxxxxx>
---
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.
I agree that passing a base overlay under the base option looks clumsy. We could pass the base node name and find its overlay ourselves here in cor_open(). In that case, we can use the existing QAPI.
Actually, there is no existing QAPI: if you don't modify qapi/*.json, user is not able to pass the option through QAPI. It's still possible to pass the option through command-line, or when create the filter internally (like we are going to do in block-stream), but not through QAPI. So, it's better to make a new QAPI parameter, to make the new option available for QMP interface.
The reason I used the existing QAPI is to make it easier for a user to operate with the traditional options and to keep things simple. So, the user shouldn't think what overlay or above-base node to pass.
If we introduce the specific BlockdevOptionsCor, what other options may come with?
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?
The base_overlay identifier is used below as the pointer to BS. The base_overlay_node stands for the name of the node. I used that identifier to differ between the types. And the above_base has another meaning per block/stream.c - it can be a temporary filter with a JSON-name.
bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
@@ -52,7 +57,16 @@ 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 (base_overlay_node) {
+ qdict_del(options, "base");
+ base_overlay = bdrv_lookup_bs(NULL, base_overlay_node, errp);
I think this is a use-after-free. The storage @base_overlay_node points
to belongs to a QString, which is referenced only by @options; so
deleting that element of @options should free that string.
Max
I will swap those two function calls (bdrv_lookup_bs(); qdict_del();).
Thank you.
Andrey
+ if (!base_overlay) {
+ error_setg(errp, QERR_BASE_NOT_FOUND, base_overlay_node);
+ return -EINVAL;
+ }
+ }
state->active = true;
+ state->base_overlay = base_overlay;
/*
* We don't need to call bdrv_child_refresh_perms() now as the permissions
--
Best regards,
Vladimir
