[Qemu-devel] Re: RFC: blockdev_add & friends, brief rationale, QMP docs

[Avi Kivity <avi@redhat.com>]

On 05/28/2010 09:21 PM, Markus Armbruster wrote:

<snip, agreed>

> Summary of the host / guest split:
>
> -drive options                      host or guest?
> bus, unit, if, index, addr          guest, already covered by qdev
> cyls, heads, secs, trans            guest, new qdev properties
>                                        (but defaults depend on image)
> media                               guest
> snapshot, file, cache, aio, format  host, blockdev_add options
>    

We expose some of the cache property to the guest.  IMO we need the 
cache property to be both guest and host, with qemu bridging the 
impedance mismatch if needed.

> rerror, werror                      host, guest drivers will reject
>                                        values they don't support
>    

Did you mean 'block format drivers will reject'?

> serial                              guest, new qdev properties
> readonly                            both host&  guest, qdev will refuse
>                                        to connect readonly host to read/
>                                        write guest
>
> QMP command docs:
>
> blockdev_add
> ------------
>
> Add host block device.
>
> Arguments:
>
> - "id": the host block device's ID, must be unique (json-string)
>    

Unique in which namespace?  A global ID namespace if fine.

> - "file": the disk image file to use (json-string, optional)
> - "format": disk format (json-string, optional)
>      - Possible values: "raw", "qcow2", ...
>    

Need some way to list supported formats.

> - "aio": host AIO (json-string, optional)
>      - Possible values: "threads" (default), "native"
>    

Need some way to list supported options.

> - "cache": host cache usage (json-string, optional)
>      - Possible values: "writethrough" (default), "writeback", "unsafe",
>                         "none"
>    

...

> - "readonly": open image read-only (json-bool, optional, default false)
> - "rerror": what to do on read error (json-string, optional)
>      - Possible values: "report" (default), "ignore", "stop"
>    

...

> - "werror": what to do on write error (json-string, optional)
>      - Possible values: "enospc" (default), "report", "ignore", "stop"
>    

...
> - "snapshot": enable snapshot (json-bool, optional, default false)
>
>    

An alternative to the "Need some way to list *" is to provide another 
query capability, akin to KVM_CAP_..., but I think listing is superior.

> Example:
>
> ->  { "execute": "blockdev_add",
>               "arguments": { "format": "raw", "id": "blk1",
>                              "file": "fedora.img" } }
> <- { "return": {} }
>
> Notes:
>
> (1) If argument "file" is missing, all other optional arguments must be
>      missing as well.  This defines a block device with no media
>      inserted.
>
> (2) It's possible to list supported disk formats by running QEMU with
>      arguments "-blockdev_add \?".
>    

Ok, so there's a partial answer here.

> blockdev_change
> ---------------
>
> Change host block device media.
>
> Arguments are exactly like blockdev_add.
>
> Notes:
>
> (1) If argument "file" is missing, all other optional arguments must be
>      missing as well.  This ejects the media without inserting a new one.
>    

Maybe we want an explicit blockdev_eject instead, not sure.

-- 
error compiling committee.c: too many arguments to function