Re: [PATCH qemu-kvm] device-assignment: add config fd qdev property

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/19/2010 02:00 PM, Chris Wright wrote:
> When libvirt launches a guest it first chowns the relevenat
> /sys/bus/pci/.../config file for an assigned device then drops privileges.
>
> This causes an issue for device assignment because despite being file
> owner, the sysfs config space file checks for CAP_SYS_ADMIN before
> allowing access to device dependent config space.
>
> This adds a new qdev configfd property which allows libvirt to open the
> sysfs config space file and give qemu an already opened file descriptor.
> Along with a change pending for the 2.6.35 kernel, this allows the
> capability check to compare against privileges from when the file was
> opened.
>
> Signed-off-by: Chris Wright<chrisw@redhat.com>
>    

An fd as a qdev property seems like a bad idea to me.  I'm not sure I 
have a better suggestion though.

Regards,

Anthony Liguori

> ---
>   hw/device-assignment.c |   12 ++++++++----
>   1 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> index eb31c78..172f0c9 100644
> --- a/hw/device-assignment.c
> +++ b/hw/device-assignment.c
> @@ -612,12 +612,15 @@ static int get_real_device(AssignedDevice *pci_dev, uint16_t r_seg,
>
>       snprintf(name, sizeof(name), "%sconfig", dir);
>
> -    fd = open(name, O_RDWR);
> +    fd = dev->config_fd;
>       if (fd == -1) {
> -        fprintf(stderr, "%s: %s: %m\n", __func__, name);
> -        return 1;
> +        fd = open(name, O_RDWR);
> +        if (fd == -1) {
> +            fprintf(stderr, "%s: %s: %m\n", __func__, name);
> +            return 1;
> +        }
> +        dev->config_fd = fd;
>       }
> -    dev->config_fd = fd;
>   again:
>       r = read(fd, pci_dev->dev.config, pci_config_size(&pci_dev->dev));
>       if (r<  0) {
> @@ -1433,6 +1436,7 @@ static PCIDeviceInfo assign_info = {
>       .qdev.props   = (Property[]) {
>           DEFINE_PROP("host", AssignedDevice, host, qdev_prop_hostaddr, PCIHostDevice),
>           DEFINE_PROP_UINT32("iommu", AssignedDevice, use_iommu, 1),
> +        DEFINE_PROP_INT32("configfd", AssignedDevice, real_device.config_fd, -1),
>           DEFINE_PROP_END_OF_LIST(),
>       },
>   };
> --
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