[Libguestfs] [PATCH nbdkit v2 5/6] New plugin: ones

[Eric Blake]

On Wed, May 17, 2023 at 11:06:58AM +0100, Richard W.M. Jones wrote:
> Returns a fully allocated disk containing all 0xff (all ones), or
> another byte of your choice.
> ---
>  plugins/data/nbdkit-data-plugin.pod           |   1 +
>  plugins/full/nbdkit-full-plugin.pod           |   1 +
>  plugins/null/nbdkit-null-plugin.pod           |   1 +
>  plugins/ones/nbdkit-ones-plugin.pod           |  77 +++++++
>  plugins/pattern/nbdkit-pattern-plugin.pod     |   4 +-
>  plugins/random/nbdkit-random-plugin.pod       |   1 +
>  .../nbdkit-sparse-random-plugin.pod           |   1 +
>  plugins/zero/nbdkit-zero-plugin.pod           |   1 +
>  configure.ac                                  |   2 +
>  plugins/ones/Makefile.am                      |  70 +++++++
>  tests/Makefile.am                             |   4 +
>  plugins/ones/ones.c                           | 191 ++++++++++++++++++
>  tests/test-ones.sh                            |  53 +++++
>  13 files changed, 406 insertions(+), 1 deletion(-)
> 
> +++ b/plugins/ones/ones.c
> @@ -0,0 +1,191 @@

> +
> +/* Write zeroes. */
> +static int
> +ones_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
> +{
> +  /* nothing */
> +  return 0;
> +}

Since writing zeroes is a no-op...

> +static struct nbdkit_plugin plugin = {
> +  .name              = "ones",
> +  .version           = PACKAGE_VERSION,
> +  .config            = ones_config,
> +  .config_help       = ones_config_help,
> +  .magic_config_key  = "size",
> +  .open              = ones_open,
> +  .get_size          = ones_get_size,
> +  .can_multi_conn    = ones_can_multi_conn,
> +  .can_cache         = ones_can_cache,
> +  .pread             = ones_pread,
> +  .pwrite            = ones_pwrite,
> +  .zero              = ones_zero,
> +  .trim              = ones_trim,
> +  .can_fua           = ones_can_fua,
> +  .flush             = ones_flush,
> +  .extents           = ones_extents,
> +  /* In this plugin, errno is preserved properly along error return
> +   * paths from failed system calls.
> +   */
> +  .errno_is_preserved = 1,
> +};

...we probably also want to supply .can_fast_zero with a function that
returns true.


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org