Re: [Qemu-devel] [Qemu-block] [PATCH 09/19] test-bdrv-drain: Add test for node deletion

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Apr 11, 2018 at 06:39:30PM +0200, Kevin Wolf wrote:
> +static void do_test_delete_by_drain(bool detach_instead_of_delete)
> +{
> +    BlockBackend *blk;
> +    BlockDriverState *bs, *child_bs, *null_bs;
> +    BDRVTestTopState *tts;
> +    TestCoDeleteByDrainData dbdd;
> +    Coroutine *co;
> +
> +    bs = bdrv_new_open_driver(&bdrv_test_top_driver, "top", BDRV_O_RDWR,
> +                              &error_abort);
> +    bs->total_sectors = 65536 >> BDRV_SECTOR_BITS;
> +    tts = bs->opaque;
> +
> +    null_bs = bdrv_open("null-co://", NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
> +                        &error_abort);
> +    bdrv_attach_child(bs, null_bs, "null-child", &child_file, &error_abort);
> +
> +    /* This child will be the one to pass to requests through to, and
> +     * it will stall until a drain occurs */
> +    child_bs = bdrv_new_open_driver(&bdrv_test, "child", BDRV_O_RDWR,
> +                                    &error_abort);
> +    child_bs->total_sectors = 65536 >> BDRV_SECTOR_BITS;
> +    /* Takes our reference to child_bs */
> +    tts->wait_child = bdrv_attach_child(bs, child_bs, "wait-child", &child_file,
> +                                        &error_abort);
> +
> +    /* This child is just there to be deleted
> +     * (for detach_instead_of_delete == true) */
> +    null_bs = bdrv_open("null-co://", NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
> +                        &error_abort);
> +    bdrv_attach_child(bs, null_bs, "null-child", &child_file, &error_abort);

Why is null_bs created twice (with the exact same "null-child" name)?
I'm surprised that bdrv_attach_child() succeeds with a duplicate name.
Anyway, I find the duplicate null_bs confusing and I'm not sure if it's
a copy-paste mistake.

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