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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 19:18:28 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 |
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@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.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. MaxI 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
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