[Bug 1906463] [NEW] "-device help" does not report all devices

[Bug 1906463] [NEW] "-device help" does not report all devices

[Doug Evans]

Public bug reported:

-device help doesn't report all devices.
E.g., devices that are instantiated by a board don't get printed in part because they don't exist when "-device help" is processed. As an experiment I deferred processing of "-device help" as long as possible and some devices were still not printed, so there's more going on here.

QEMU commit hash: 944fdc5e27a5b5adbb765891e8e70e88ba9a00ec

Repro:
$ configure --target-list=arm-softmmu
$ make
$ ./qemu-system-arm -device help | grep npcm7xx
<empty>

I'd expect to see things like npcm7xx-rng in the output.

I can imagine enumerating board-provided devices is a challenge.
Still, it'd be really nice if "-device help" printed them, and having
"-device $driver,help" work as well.

** Affects: qemu
     Importance: Undecided
         Status: New

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Title:
  "-device help" does not report all devices

Status in QEMU:
  New

Bug description:
  -device help doesn't report all devices.
  E.g., devices that are instantiated by a board don't get printed in part because they don't exist when "-device help" is processed. As an experiment I deferred processing of "-device help" as long as possible and some devices were still not printed, so there's more going on here.

  QEMU commit hash: 944fdc5e27a5b5adbb765891e8e70e88ba9a00ec

  Repro:
  $ configure --target-list=arm-softmmu
  $ make
  $ ./qemu-system-arm -device help | grep npcm7xx
  <empty>

  I'd expect to see things like npcm7xx-rng in the output.

  I can imagine enumerating board-provided devices is a challenge.
  Still, it'd be really nice if "-device help" printed them, and having
  "-device $driver,help" work as well.

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Re: [Bug 1906463] [NEW] "-device help" does not report all devices

[Markus Armbruster]

Doug Evans <1906463@bugs.launchpad.net> writes:

> Public bug reported:
>
> -device help doesn't report all devices.
> E.g., devices that are instantiated by a board don't get printed in part because they don't exist when "-device help" is processed. As an experiment I deferred processing of "-device help" as long as possible and some devices were still not printed, so there's more going on here.
>
> QEMU commit hash: 944fdc5e27a5b5adbb765891e8e70e88ba9a00ec
>
> Repro:
> $ configure --target-list=arm-softmmu
> $ make
> $ ./qemu-system-arm -device help | grep npcm7xx
> <empty>
>
> I'd expect to see things like npcm7xx-rng in the output.

Works as intended.

"-device help" shows the devices that are available with -device.
npcm7xx-rng isn't:

    $ qemu-system-arm -M virt -device npcm7xx-rng
    qemu-system-arm: -device npcm7xx-rng: Parameter 'driver' expects pluggable device type

Monitor command "info qdm" shows all devices, including npcm7xx-rng:

    $ qemu-system-arm -M virt -monitor stdio
    QEMU 5.1.92 monitor - type 'help' for more information
    (qemu) info qdm
    [...]
    name "npcm7xx-rng", bus System, desc "NPCM7xx Random Number Generator", no-user
    [...]

Note "no-user": it's not available with -device.

> I can imagine enumerating board-provided devices is a challenge.
> Still, it'd be really nice if "-device help" printed them, and having
> "-device $driver,help" work as well.

It works:

    $ qemu-system-arm -M virt -device npcm7xx-rng,help
    npcm7xx-rng options:
      regs[0]=<child<qemu:memory-region>>

Hope this helps!

[Bug 1906463] Re: "-device help" does not report all devices

[Thomas Huth]

This works as intended, see Markus' reply here:
https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg00337.html


** Changed in: qemu
       Status: New => Invalid

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You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1906463

Title:
  "-device help" does not report all devices

Status in QEMU:
  Invalid

Bug description:
  -device help doesn't report all devices.
  E.g., devices that are instantiated by a board don't get printed in part because they don't exist when "-device help" is processed. As an experiment I deferred processing of "-device help" as long as possible and some devices were still not printed, so there's more going on here.

  QEMU commit hash: 944fdc5e27a5b5adbb765891e8e70e88ba9a00ec

  Repro:
  $ configure --target-list=arm-softmmu
  $ make
  $ ./qemu-system-arm -device help | grep npcm7xx
  <empty>

  I'd expect to see things like npcm7xx-rng in the output.

  I can imagine enumerating board-provided devices is a challenge.
  Still, it'd be really nice if "-device help" printed them, and having
  "-device $driver,help" work as well.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1906463/+subscriptions

Re: [Bug 1906463] [NEW] "-device help" does not report all devices

[Doug Evans]

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On Tue, Dec 1, 2020 at 10:53 PM Markus Armbruster <armbru@redhat.com> wrote:

> Doug Evans <1906463@bugs.launchpad.net> writes:
>
> > Public bug reported:
> >
> > -device help doesn't report all devices.
> > E.g., devices that are instantiated by a board don't get printed in part
> because they don't exist when "-device help" is processed. As an experiment
> I deferred processing of "-device help" as long as possible and some
> devices were still not printed, so there's more going on here.
> >
> > QEMU commit hash: 944fdc5e27a5b5adbb765891e8e70e88ba9a00ec
> >
> > Repro:
> > $ configure --target-list=arm-softmmu
> > $ make
> > $ ./qemu-system-arm -device help | grep npcm7xx
> > <empty>
> >
> > I'd expect to see things like npcm7xx-rng in the output.
>
> Works as intended.
>
> "-device help" shows the devices that are available with -device.
> npcm7xx-rng isn't:
>
>     $ qemu-system-arm -M virt -device npcm7xx-rng
>     qemu-system-arm: -device npcm7xx-rng: Parameter 'driver' expects
> pluggable device type
>
> Monitor command "info qdm" shows all devices, including npcm7xx-rng:
>
>     $ qemu-system-arm -M virt -monitor stdio
>     QEMU 5.1.92 monitor - type 'help' for more information
>     (qemu) info qdm
>     [...]
>     name "npcm7xx-rng", bus System, desc "NPCM7xx Random Number
> Generator", no-user
>     [...]
>
> Note "no-user": it's not available with -device.
>
> > I can imagine enumerating board-provided devices is a challenge.
> > Still, it'd be really nice if "-device help" printed them, and having
> > "-device $driver,help" work as well.
>
> It works:
>
>     $ qemu-system-arm -M virt -device npcm7xx-rng,help
>     npcm7xx-rng options:
>       regs[0]=<child<qemu:memory-region>>
>
> Hope this helps!
>

Thanks for the reply. It does help, but it's odd that I can't use "-device
help" to discover a device, but once discovered I can use it to get help on
that device.
At least I get why now. Thanks again.

Btw, if I may ask another dumb question, I get this:

@ruffy:build-arm$ ./qemu-system-arm -M virt -monitor stdio
Unable to init server: Could not connect: Connection refused
QEMU 5.1.93 monitor - type 'help' for more information
(qemu) gtk initialization failed
<exit>

If I add "-display none" then it works, but it's odd that it's trying to
initialize with gtk here ($DISPLAY isn't set, there is no X present).
-help output says gtk is the default for -display, I'm guessing you didn't
configure with gtk so that's why it works for you.
Question: I'm not up on what the current state of the art is here, but
given that $DISPLAY is unset, why not punt on gtk and default to "none" ?
(printing a warning at startup explaining why if that helps)

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Re: [Bug 1906463] [NEW] "-device help" does not report all devices

[Peter Maydell]

On Wed, 2 Dec 2020 at 16:51, Doug Evans <dje@google.com> wrote:
>
> Btw, if I may ask another dumb question, I get this:
>
> @ruffy:build-arm$ ./qemu-system-arm -M virt -monitor stdio
> Unable to init server: Could not connect: Connection refused
> QEMU 5.1.93 monitor - type 'help' for more information
> (qemu) gtk initialization failed
> <exit>
>
> If I add "-display none" then it works, but it's odd that it's trying to initialize with gtk here ($DISPLAY isn't set, there is no X present).

That's expected. By default we try to create a GUI window.
If DISPLAY is not set, then that fails, which is why
we print "gtk initialization failed" and exit.
This is the same behaviour as other GUI apps:

$ DISPLAY= xterm
xterm: Xt error: Can't open display:
xterm: DISPLAY is not set

$ DISPLAY= firefox
Unable to init server: Broadway display type not supported:
Error: cannot open display:

$ DISPLAY= evince
Unable to init server: Could not connect: Connection refused
Cannot parse arguments: Cannot open display:

If you don't want graphics you should tell QEMU you
don't want graphics (eg with '-display none').

This seems to me more helpful to most users than the
alternative (if you know you don't want the GUI then
it's easy to disable it; but most non-sophisticated
users do want it).

thanks
-- PMM

Re: [Bug 1906463] [NEW] "-device help" does not report all devices

[Doug Evans]

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On Wed, Dec 2, 2020 at 9:41 AM Peter Maydell <peter.maydell@linaro.org>
wrote:

> On Wed, 2 Dec 2020 at 16:51, Doug Evans <dje@google.com> wrote:
> >
> > Btw, if I may ask another dumb question, I get this:
> >
> > @ruffy:build-arm$ ./qemu-system-arm -M virt -monitor stdio
> > Unable to init server: Could not connect: Connection refused
> > QEMU 5.1.93 monitor - type 'help' for more information
> > (qemu) gtk initialization failed
> > <exit>
> >
> > If I add "-display none" then it works, but it's odd that it's trying to
> initialize with gtk here ($DISPLAY isn't set, there is no X present).
>
> That's expected. By default we try to create a GUI window.
> If DISPLAY is not set, then that fails, which is why
> we print "gtk initialization failed" and exit.
> This is the same behaviour as other GUI apps:
>
> $ DISPLAY= xterm
> xterm: Xt error: Can't open display:
> xterm: DISPLAY is not set
>
> $ DISPLAY= firefox
> Unable to init server: Broadway display type not supported:
> Error: cannot open display:
>
> $ DISPLAY= evince
> Unable to init server: Could not connect: Connection refused
> Cannot parse arguments: Cannot open display:
>
> If you don't want graphics you should tell QEMU you
> don't want graphics (eg with '-display none').
>
> This seems to me more helpful to most users than the
> alternative (if you know you don't want the GUI then
> it's easy to disable it; but most non-sophisticated
> users do want it).
>


Thanks. That's not unreasonable.

OTOH, all those examples don't have a non-X mode.
As counterexamples there's emacs and gvim.

The present situation is fine, now that I understand it.
I can write a wrapper that DTRT.

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