Re: [PATCH 04/11] qemu-options: finesse the recommendations around -blockdev

[Markus Armbruster]

Alex Bennée <alex.bennee@linaro.org> writes:

> We are a bit premature in recommending -blockdev/-device as the best
> way to configure block devices, especially in the common case.
> Improve the language to hopefully make things clearer.
>
> Suggested-by: Michael Tokarev <mjt@tls.msk.ru>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  qemu-options.hx | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 59bdf67a2c..9a69ed838e 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1143,10 +1143,14 @@ have gone through several iterations as the feature 
> set and complexity
>  of the block layer have grown. Many online guides to QEMU often
>  reference older and deprecated options, which can lead to confusion.
>  
> -The recommended modern way to describe disks is to use a combination of
> +The most explicit way to describe disks is to use a combination of
>  ``-device`` to specify the hardware device and ``-blockdev`` to
>  describe the backend. The device defines what the guest sees and the
> -backend describes how QEMU handles the data.
> +backend describes how QEMU handles the data. The ``-drive`` option
> +combines the device and backend into a single command line options
> +which is useful in the majority of cases.

-drive may look simpler from afar, but it really is a hot mess.  Sadly,
we can't get rid of it until we find a replacement for configuring
onboard block devices.  We might be able to clean it up some if we
accept compatibility breaks.  A new convenience option would be less
confusing, I guess.

>                                            Older options like ``-hda``
> +bake in a lot of assumptions from the days when QEMU was emulating a
> +legacy PC, they are not recommended for modern configurations.
>  
>  ERST

These older options and the non-option argument are simple macros for
-drive:

    IMG-FILE                    -drive index=0,file=IMG-FILE,media=disk
    -hda IMG-FILE               -drive index=0,file=IMG-FILE,media=disk
    -hdb IMG-FILE               -drive index=1,file=IMG-FILE,media=disk
    -hdc IMG-FILE               -drive index=2,file=IMG-FILE,media=disk
    -hdd IMG-FILE               -drive index=3,file=IMG-FILE,media=disk
    -cdrom IMG-FILE             -drive index=2,file=IMG-FILE,media=cdrom
    -fda IMG-FILE               -drive if=floppy,index=0,file=IMG-FILE
    -fdb IMG-FILE               -drive if=floppy,index=1,file=IMG-FILE
    -mtdblock IMG-FILE          -drive if=mtd,file=IMG-FILE
    -sd IMG-FILE                -drive if=sd,file=IMG-FILE
    -pflash IMG-FILE            -drive if=pflash,file=IMG-FILE

What assumptions do you have in mind?

I think you need at least Kevin's Acked-by for this.