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

[Vladimir Sementsov-Ogievskiy]

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?

> +
> +    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>

--
Best regards,
Vladimir