Re: [PATCH 02/18] fuse: Allow exporting BDSs via FUSE

[Kevin Wolf <kwolf@redhat.com>]

Am 19.12.2019 um 15:38 hat Max Reitz geschrieben:
> fuse-export-add allows mounting block graph nodes via FUSE on some
> existing regular file.  That file should then appears like a raw disk
> image, and accesses to it result in accesses to the exported BDS.
> 
> Right now, we only set up the mount point and tear all mount points down
> in bdrv_close_all().  We do not implement any access functions, so
> accessing the mount point only results in errors.  This will be
> addressed by a followup patch.
> 
> The set of exported nodes is kept in a hash table so we can later add a
> fuse-export-remove that allows unmounting.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>

> diff --git a/qapi/block.json b/qapi/block.json
> index 145c268bb6..03f8d1b537 100644
> --- a/qapi/block.json
> +++ b/qapi/block.json
> @@ -317,6 +317,29 @@
>  ##
>  { 'command': 'nbd-server-stop' }
>  
> +##
> +# @fuse-export-add:
> +#
> +# Exports a block graph node on some (file) mountpoint as a raw image.
> +#
> +# @node-name: Node to be exported
> +#
> +# @mountpoint: Path on which to export the block device via FUSE.
> +#              This must point to an existing regular file.
> +#
> +# @writable: Whether clients should be able to write to the block
> +#            device via the FUSE export. (default: false)
> +#
> +# Since: 5.0
> +##
> +{ 'command': 'fuse-export-add',
> +  'data': {
> +      'node-name': 'str',
> +      'mountpoint': 'str',
> +      '*writable': 'bool'
> +  },
> +  'if': 'defined(CONFIG_FUSE)' }

Can this use a BlockExport union from the start like I'm introducing in
the storage daemon series, together with a generic block-export-add?

It also looks like node-name and writable should be part of the common
base of BlockExport. Unfortunately this would mean that I can't use the
same BlockExportNbd for the existing nbd-server-add command any more. I
guess I could somehow get a shared base type for both, though.

Markus, any thoughts on these QAPI interfaces?

Kevin