Re: [PATCH v3 18/36] block: add bdrv_attach_child_common() transaction action

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

26.04.2021 19:14, Kevin Wolf wrote:
> Am 17.03.2021 um 15:35 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> Split out no-perm part of bdrv_root_attach_child() into separate
>> transaction action. bdrv_root_attach_child() now moves to new
>> permission update paradigm: first update graph relations then update
>> permissions.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>   block.c | 189 ++++++++++++++++++++++++++++++++++++++++----------------
>>   1 file changed, 135 insertions(+), 54 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 98ff44dbf7..b6bdc534d2 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -2921,37 +2921,73 @@ static void bdrv_replace_child(BdrvChild *child, BlockDriverState *new_bs)
>>       }
>>   }
>>   
>> -/*
>> - * This function steals the reference to child_bs from the caller.
>> - * That reference is later dropped by bdrv_root_unref_child().
>> - *
>> - * On failure NULL is returned, errp is set and the reference to
>> - * child_bs is also dropped.
>> - *
>> - * The caller must hold the AioContext lock @child_bs, but not that of @ctx
>> - * (unless @child_bs is already in @ctx).
>> - */
>> -BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
>> -                                  const char *child_name,
>> -                                  const BdrvChildClass *child_class,
>> -                                  BdrvChildRole child_role,
>> -                                  uint64_t perm, uint64_t shared_perm,
>> -                                  void *opaque, Error **errp)
>> +static void bdrv_remove_empty_child(BdrvChild *child)
>>   {
>> -    BdrvChild *child;
>> -    Error *local_err = NULL;
>> -    int ret;
>> -    AioContext *ctx;
>> +    assert(!child->bs);
>> +    QLIST_SAFE_REMOVE(child, next);
>> +    g_free(child->name);
>> +    g_free(child);
>> +}
>>   
>> -    ret = bdrv_check_update_perm(child_bs, NULL, perm, shared_perm, NULL, errp);
>> -    if (ret < 0) {
>> -        bdrv_abort_perm_update(child_bs);
>> -        bdrv_unref(child_bs);
>> -        return NULL;
>> +typedef struct BdrvAttachChildCommonState {
>> +    BdrvChild **child;
>> +    AioContext *old_parent_ctx;
>> +    AioContext *old_child_ctx;
>> +} BdrvAttachChildCommonState;
>> +
>> +static void bdrv_attach_child_common_abort(void *opaque)
>> +{
>> +    BdrvAttachChildCommonState *s = opaque;
>> +    BdrvChild *child = *s->child;
>> +    BlockDriverState *bs = child->bs;
>> +
>> +    bdrv_replace_child_noperm(child, NULL);
>> +
>> +    if (bdrv_get_aio_context(bs) != s->old_child_ctx) {
>> +        bdrv_try_set_aio_context(bs, s->old_child_ctx, &error_abort);
>>       }
>>   
>> -    child = g_new(BdrvChild, 1);
>> -    *child = (BdrvChild) {
>> +    if (bdrv_child_get_parent_aio_context(child) != s->old_parent_ctx) {
>> +        GSList *ignore = g_slist_prepend(NULL, child);
>> +
>> +        child->klass->can_set_aio_ctx(child, s->old_parent_ctx, &ignore,
>> +                                      &error_abort);
>> +        g_slist_free(ignore);
>> +        ignore = g_slist_prepend(NULL, child);
>> +        child->klass->set_aio_ctx(child, s->old_parent_ctx, &ignore);
>> +
>> +        g_slist_free(ignore);
>> +    }
>> +
>> +    bdrv_unref(bs);
>> +    bdrv_remove_empty_child(child);
>> +    *s->child = NULL;
>> +}
>> +
>> +static TransactionActionDrv bdrv_attach_child_common_drv = {
>> +    .abort = bdrv_attach_child_common_abort,
>> +};
>> +
>> +/*
>> + * Common part of attoching bdrv child to bs or to blk or to job
>> + */
>> +static int bdrv_attach_child_common(BlockDriverState *child_bs,
>> +                                    const char *child_name,
>> +                                    const BdrvChildClass *child_class,
>> +                                    BdrvChildRole child_role,
>> +                                    uint64_t perm, uint64_t shared_perm,
>> +                                    void *opaque, BdrvChild **child,
>> +                                    Transaction *tran, Error **errp)
>> +{
>> +    BdrvChild *new_child;
>> +    AioContext *parent_ctx;
>> +    AioContext *child_ctx = bdrv_get_aio_context(child_bs);
>> +
>> +    assert(child);
>> +    assert(*child == NULL);
>> +
>> +    new_child = g_new(BdrvChild, 1);
>> +    *new_child = (BdrvChild) {
>>           .bs             = NULL,
>>           .name           = g_strdup(child_name),
>>           .klass          = child_class,
>> @@ -2961,37 +2997,92 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
>>           .opaque         = opaque,
>>       };
>>   
>> -    ctx = bdrv_child_get_parent_aio_context(child);
>> -
>> -    /* If the AioContexts don't match, first try to move the subtree of
>> +    /*
>> +     * If the AioContexts don't match, first try to move the subtree of
>>        * child_bs into the AioContext of the new parent. If this doesn't work,
>> -     * try moving the parent into the AioContext of child_bs instead. */
>> -    if (bdrv_get_aio_context(child_bs) != ctx) {
>> -        ret = bdrv_try_set_aio_context(child_bs, ctx, &local_err);
>> +     * try moving the parent into the AioContext of child_bs instead.
>> +     */
>> +    parent_ctx = bdrv_child_get_parent_aio_context(new_child);
>> +    if (child_ctx != parent_ctx) {
>> +        Error *local_err = NULL;
>> +        int ret = bdrv_try_set_aio_context(child_bs, parent_ctx, &local_err);
>> +
>>           if (ret < 0 && child_class->can_set_aio_ctx) {
>> -            GSList *ignore = g_slist_prepend(NULL, child);
>> -            ctx = bdrv_get_aio_context(child_bs);
>> -            if (child_class->can_set_aio_ctx(child, ctx, &ignore, NULL)) {
>> +            GSList *ignore = g_slist_prepend(NULL, new_child);
>> +            if (child_class->can_set_aio_ctx(new_child, child_ctx, &ignore,
>> +                                             NULL))
>> +            {
>>                   error_free(local_err);
>>                   ret = 0;
>>                   g_slist_free(ignore);
>> -                ignore = g_slist_prepend(NULL, child);
>> -                child_class->set_aio_ctx(child, ctx, &ignore);
>> +                ignore = g_slist_prepend(NULL, new_child);
>> +                child_class->set_aio_ctx(new_child, child_ctx, &ignore);
>>               }
>>               g_slist_free(ignore);
>>           }
>> +
>>           if (ret < 0) {
>>               error_propagate(errp, local_err);
>> -            g_free(child);
>> -            bdrv_abort_perm_update(child_bs);
>> -            bdrv_unref(child_bs);
>> -            return NULL;
>> +            bdrv_remove_empty_child(new_child);
>> +            return ret;
>>           }
>>       }
>>   
>> -    /* This performs the matching bdrv_set_perm() for the above check. */
>> -    bdrv_replace_child(child, child_bs);
>> +    bdrv_ref(child_bs);
>> +    bdrv_replace_child_noperm(new_child, child_bs);
>> +
>> +    *child = new_child;
>>   
>> +    BdrvAttachChildCommonState *s = g_new(BdrvAttachChildCommonState, 1);
>> +    *s = (BdrvAttachChildCommonState) {
>> +        .child = child,
>> +        .old_parent_ctx = parent_ctx,
>> +        .old_child_ctx = child_ctx,
>> +    };
>> +    tran_add(tran, &bdrv_attach_child_common_drv, s);
> 
> Who frees s? Should bdrv_attach_child_common_drv have a .clean?
> 

Hmm, yes, looks like ".clean = g_free" missed.

-- 
Best regards,
Vladimir