Re: [Qemu-devel] [PATCH 04/10] x86,MIPS: make vmware_vga optional

[Markus Armbruster]

Blue Swirl <address@hidden> writes:

> Allow failure with vmware_vga device creation and use standard
> VGA instead.
>
> Signed-off-by: Blue Swirl <address@hidden>
> ---
>  hw/mips_malta.c |    6 +++++-
>  hw/pc.c         |   11 ++++++++---
>  hw/vmware_vga.h |   11 +++++++++--
>  3 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/hw/mips_malta.c b/hw/mips_malta.c
> index 2d3f242..930c51c 100644
> --- a/hw/mips_malta.c
> +++ b/hw/mips_malta.c
> @@ -957,7 +957,11 @@ void mips_malta_init (ram_addr_t ram_size,
>      if (cirrus_vga_enabled) {
>          pci_cirrus_vga_init(pci_bus);
>      } else if (vmsvga_enabled) {
> -        pci_vmsvga_init(pci_bus);
> +        if (!pci_vmsvga_init(pci_bus)) {
> +            fprintf(stderr, "Warning: vmware_vga not available,"
> +                    " using standard VGA instead\n");
> +            pci_vga_init(pci_bus);
> +        }
>      } else if (std_vga_enabled) {
>          pci_vga_init(pci_bus);
>      }
> diff --git a/hw/pc.c b/hw/pc.c
> index 4dfdc0b..fcee09a 100644
> --- a/hw/pc.c
> +++ b/hw/pc.c
> @@ -1053,10 +1053,15 @@ void pc_vga_init(PCIBus *pci_bus)
>              isa_cirrus_vga_init();
>          }
>      } else if (vmsvga_enabled) {
> -        if (pci_bus)
> -            pci_vmsvga_init(pci_bus);
> -        else
> +        if (pci_bus) {
> +            if (!pci_vmsvga_init(pci_bus)) {
> +                fprintf(stderr, "Warning: vmware_vga not available,"
> +                        " using standard VGA instead\n");

I don't like "vmware_vga" here.  The command line option that makes us
go here is spelled "-vga vmware", and the qdev is called "vmware-svga".
What about "-vga vmware is not available"?

> +                pci_vga_init(pci_bus);
> +            }
> +        } else {
>              fprintf(stderr, "%s: vmware_vga: no PCI bus\n", __FUNCTION__);
> +        }
>  #ifdef CONFIG_SPICE
>      } else if (qxl_enabled) {
>          if (pci_bus)
> diff --git a/hw/vmware_vga.h b/hw/vmware_vga.h
> index e7bcb22..5132573 100644
> --- a/hw/vmware_vga.h
> +++ b/hw/vmware_vga.h
> @@ -4,9 +4,16 @@
>  #include "qemu-common.h"
>
>  /* vmware_vga.c */
> -static inline void pci_vmsvga_init(PCIBus *bus)
> +static inline bool pci_vmsvga_init(PCIBus *bus)
>  {
> -    pci_create_simple(bus, -1, "vmware-svga");
> +    PCIDevice *dev;
> +
> +    dev = pci_try_create(bus, -1, "vmware-svga");
> +    if (!dev || qdev_init(&dev->qdev) < 0) {
> +        return false;
> +    } else {
> +        return true;
> +    }
>  }
>
>  #endif

Two failure modes:

* pci_try_create() fails, which can happen only if no such qdev
  "vmware-svga" exists.

* qdev_init() fails.

The caller can't distinguish between the two, and assumes any failure
must be the former.

The assumption is actually correct, because pci_vmsvga_initfn() never
fails, and thus qdev_init() never fails.  Brittle.


pci_vmsvga_init() is a convenience function for board setup code.  Why
not make it more convenient and concentrate the error handling there
rather than duplicating it in each caller?

Nice side effect: no need to conflate the failure modes, no need for the
brittle assumption.