Re: [PATCH v6 2/4] copy-on-read: add filter append/drop functions

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

On 19.08.2020 13:21, Vladimir Sementsov-Ogievskiy wrote:
> 19.08.2020 00:24, Andrey Shinkevich wrote:
>> Provide API for the COR-filter insertion/removal.
>> Also, drop the filter child permissions for an inactive state when the
>> filter node is being removed.
>>
>> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
>> ---
>>   block/copy-on-read.c | 103 
>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>>   block/copy-on-read.h |  36 ++++++++++++++++++
>>   2 files changed, 139 insertions(+)
>>   create mode 100644 block/copy-on-read.h
>>
>> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
>> index cb03e0f..150d9b7 100644
>> --- a/block/copy-on-read.c
>> +++ b/block/copy-on-read.c
>> @@ -23,11 +23,21 @@
>>   #include "qemu/osdep.h"
>>   #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;
>> +} BDRVStateCOR;
>>       static int cor_open(BlockDriverState *bs, QDict *options, int 
>> flags,
>>                       Error **errp)
>>   {
>> +    BDRVStateCOR *state = bs->opaque;
>> +
>>       bs->file = bdrv_open_child(NULL, options, "file", bs, 
>> &child_of_bds,
>>                                  BDRV_CHILD_FILTERED | 
>> BDRV_CHILD_PRIMARY,
>>                                  false, errp);
>> @@ -42,6 +52,8 @@ 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);
>>   +    state->active = true;
>
> We don't need to call bdrv_child_refresh_perms() here, as permissions 
> will be
> updated soon, when the filter node get its parent, yes?
>
> Let's add at least a comment on this.
>
>> +
>>       return 0;
>>   }
>>   @@ -57,6 +69,17 @@ static void cor_child_perm(BlockDriverState *bs, 
>> BdrvChild *c,
>>                              uint64_t perm, uint64_t shared,
>>                              uint64_t *nperm, uint64_t *nshared)
>>   {
>> +    BDRVStateCOR *s = bs->opaque;
>> +
>> +    if (!s->active) {
>> +        /*
>> +         * While the filter is being removed
>> +         */
>> +        *nperm = 0;
>> +        *nshared = BLK_PERM_ALL;
>> +        return;
>> +    }
>> +
>>       *nperm = perm & PERM_PASSTHROUGH;
>>       *nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
>>   @@ -135,6 +158,7 @@ static void cor_lock_medium(BlockDriverState 
>> *bs, bool locked)
>>     static BlockDriver bdrv_copy_on_read = {
>>       .format_name                        = "copy-on-read",
>> +    .instance_size                      = sizeof(BDRVStateCOR),
>>         .bdrv_open                          = cor_open,
>>       .bdrv_child_perm                    = cor_child_perm,
>> @@ -159,4 +183,83 @@ static void bdrv_copy_on_read_init(void)
>>       bdrv_register(&bdrv_copy_on_read);
>>   }
>>   +
>> +static BlockDriverState *create_filter_node(BlockDriverState *bs,
>> +                                            const char 
>> *filter_node_name,
>> +                                            Error **errp)
>> +{
>> +    QDict *opts = qdict_new();
>> +
>> +    qdict_put_str(opts, "driver", "copy-on-read");
>> +    qdict_put_str(opts, "file", bdrv_get_node_name(bs));
>> +    if (filter_node_name) {
>> +        qdict_put_str(opts, "node-name", filter_node_name);
>> +    }
>> +
>> +    return bdrv_open(NULL, NULL, opts, BDRV_O_RDWR, errp);
>> +}
>> +
>> +
>> +BlockDriverState *bdrv_cor_filter_append(BlockDriverState *bs,
>> +                                         const char *filter_node_name,
>> +                                         Error **errp)
>> +{
>> +    BlockDriverState *cor_filter_bs;
>> +    BDRVStateCOR *state;
>> +    Error *local_err = NULL;
>> +
>> +    cor_filter_bs = create_filter_node(bs, filter_node_name, errp);
>> +    if (cor_filter_bs == NULL) {
>> +        error_prepend(errp, "Could not create filter node: ");
>> +        return NULL;
>> +    }
>> +
>> +    if (!filter_node_name) {
>> +        cor_filter_bs->implicit = true;
>> +    }
>> +
>> +    bdrv_drained_begin(bs);
>> +    bdrv_replace_node(bs, cor_filter_bs, &local_err);
>> +    bdrv_drained_end(bs);
>> +
>> +    if (local_err) {
>> +        bdrv_unref(cor_filter_bs);
>> +        error_propagate(errp, local_err);
>> +        return NULL;
>> +    }
>> +
>> +    state = cor_filter_bs->opaque;
>> +    state->active = true;
>
> hmm stop. it's already active, after create_filter_node, so you don't 
> need to set it again, isn't it?


I will remove the extra assignment from the cor_open() for consistancy.

Andrey


>
>> +
>> +    return cor_filter_bs;
>> +}
>> +
>> +
>> +void bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs)
>> +{
>> +    BdrvChild *child;
>> +    BlockDriverState *bs;
>> +    BDRVStateCOR *s = cor_filter_bs->opaque;
>> +
>> +    child = bdrv_filter_child(cor_filter_bs);
>> +    if (!child) {
>> +        return;
>> +    }
>> +    bs = child->bs;
>> +
>> +    /* Retain the BDS until we complete the graph change. */
>> +    bdrv_ref(bs);
>> +    /* Hold a guest back from writing while permissions are being 
>> reset. */
>> +    bdrv_drained_begin(bs);
>> +    /* Drop permissions before the graph change. */
>> +    s->active = false;
>> +    bdrv_child_refresh_perms(cor_filter_bs, child, &error_abort);
>> +    bdrv_replace_node(cor_filter_bs, bs, &error_abort);
>> +
>> +    bdrv_drained_end(bs);
>> +    bdrv_unref(bs);
>> +    bdrv_unref(cor_filter_bs);
>> +}
>> +
>> +
>>   block_init(bdrv_copy_on_read_init);
>> diff --git a/block/copy-on-read.h b/block/copy-on-read.h
>> new file mode 100644
>> index 0000000..db03c6c
>> --- /dev/null
>> +++ b/block/copy-on-read.h
>> @@ -0,0 +1,36 @@
>> +/*
>> + * Copy-on-read filter block driver
>> + *
>> + * The filter driver performs Copy-On-Read (COR) operations
>> + *
>> + * Copyright (c) 2018-2020 Virtuozzo International GmbH.
>> + *
>> + * Author:
>> + *   Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License as published by
>> + * the Free Software Foundation; either version 2 of the License, or
>> + * (at your option) any later version.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program. If not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>> +#ifndef COPY_ON_READ_FILTER
>> +#define COPY_ON_READ_FILTER
>> +
>> +#include "block/block_int.h"
>> +#include "block/block-copy.h"
>
> do you really need block-copy.h ?
>
>> +
>> +BlockDriverState *bdrv_cor_filter_append(BlockDriverState *bs,
>> +                                         const char *filter_node_name,
>> +                                         Error **errp);
>> +void bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs);
>> +
>> +#endif /* COPY_ON_READ_FILTER */
>>
>
> Code seems correct to me, with extra "state->active = true;" dropped:
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>