Re: [PATCH] block: nbd: Fix dirty bitmap context name

[Kevin Wolf]

Am 19.12.2019 um 14:41 hat Vladimir Sementsov-Ogievskiy geschrieben:
> Ahh, I see, it's documented as
> 
> +# @bitmap: Also export the dirty bitmap reachable from @device, so the
> +#          NBD client can use NBD_OPT_SET_META_CONTEXT with
> +#          "qemu:dirty-bitmap:NAME" to inspect the bitmap. (since 4.0)
> 
> and it is logical to assume that export name (which is @name argument) is
> mentioned. But we never mentioned it. This is just documented after
> removed experimenatl command x-nbd-server-add-bitmap,
> 
> look at
> 
> commit 7dc570b3806e5b0a4c9219061556ed5a4a0de80c
> Author: Eric Blake <address@hidden>
> Date:   Fri Jan 11 13:47:18 2019 -0600
> 
>      nbd: Remove x-nbd-server-add-bitmap
> 
> ...
> 
> -# @bitmap-export-name: How the bitmap will be seen by nbd clients
> -#                      (default @bitmap)
> -#
> -# Note: the client must use NBD_OPT_SET_META_CONTEXT with a query of
> -# "qemu:dirty-bitmap:NAME" (where NAME matches @bitmap-export-name) to access
> -# the exposed bitmap.
> 
> 
> So, this "NAME" is saved and now looks incorrect. What should be fixed, is 
> Qapi
> documentation.

Hm, I don't know these interfaces very well, but from you explanation it
looks to me as if having a bitmap name made sense with
x-nbd-server-add-bitmap because it could be called more than once for
exporting multiple bitmaps.

But now, we have only nbd-server-add, which takes a single bitmap name.
As we don't have to distinguish multiple bitmaps any more, wouldn't it
make more sense to use "qemu:dirty-bitmap" without any other
information? Both export name and bitmap name are already identified by
the connection.

But if we have to have something there, using the bitmap name (which may
or may not be the same as used in the image file) makes a little more
sense because it makes the interface extensible for the case that we
ever want to re-introduce an nbd-server-add-bitmap.

(By the way, even if the patch were correct, it lacks a Signed-off-by.)

Kevin