Re: [PATCH v1 3/7] xen: xenstore: add possibility to preserve owner

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 10/11/2023 15:42, Volodymyr Babchuk wrote:
> Add option to preserve owner when creating an entry in Xen Store. This
> may be needed in cases when Qemu is working as device model in a
> domain that is Domain-0, e.g. in driver domain.
>
> "owner" parameter for qemu_xen_xs_create() function can have special
> value XS_PRESERVE_OWNER, which will make specific implementation to
> get original owner of an entry and pass it back to
> set_permissions() call.
If QEMU is running in a driver domain then it should know whether the 
domid of the domain it is running in and use that. Yes, it is hardcoded 
to 0 at the moment but surely a backend domid (which defaults to 0) 
could be passed on the command line?
  Paul

> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> ---
>   hw/i386/kvm/xen_xenstore.c       | 18 ++++++++++++++++++
>   hw/xen/xen-operations.c          | 12 ++++++++++++
>   include/hw/xen/xen_backend_ops.h |  2 ++
>   3 files changed, 32 insertions(+)
>
> diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
> index 660d0b72f9..7b894a9884 100644
> --- a/hw/i386/kvm/xen_xenstore.c
> +++ b/hw/i386/kvm/xen_xenstore.c
> @@ -1572,6 +1572,24 @@ static bool xs_be_create(struct qemu_xs_handle *h, 
> xs_transaction_t t,
>           return false;
>       }
>   
> +    if (owner == XS_PRESERVE_OWNER) {
> +        GList *perms;
> +        char letter;
> +
> +        err = xs_impl_get_perms(h->impl, 0, t, path, &perms);
> +        if (err) {
> +            errno = err;
> +            return false;
> +        }
> +
> +        if (sscanf(perms->data, "%c%u", &letter, &owner) != 2) {
> +            errno = EFAULT;
> +            g_list_free_full(perms, g_free);
> +            return false;
> +        }
> +        g_list_free_full(perms, g_free);
> +    }
> +
>       perms_list = g_list_append(perms_list,
>                                  xs_perm_as_string(XS_PERM_NONE, owner));
>       perms_list = g_list_append(perms_list,
> diff --git a/hw/xen/xen-operations.c b/hw/xen/xen-operations.c
> index e00983ec44..1df59b3c08 100644
> --- a/hw/xen/xen-operations.c
> +++ b/hw/xen/xen-operations.c
> @@ -300,6 +300,18 @@ static bool libxenstore_create(struct qemu_xs_handle *h, 
> xs_transaction_t t,
>           return false;
>       }
>   
> +    if (owner == XS_PRESERVE_OWNER) {
> +        struct xs_permissions *tmp;
> +        unsigned int num;
> +
> +        tmp = xs_get_permissions(h->xsh, 0, path, &num);
> +        if (tmp == NULL) {
> +            return false;
> +        }
> +        perms_list[0].id = tmp[0].id;
> +        free(tmp);
> +    }
> +
>       return xs_set_permissions(h->xsh, t, path, perms_list,
>                                 ARRAY_SIZE(perms_list));
>   }
> diff --git a/include/hw/xen/xen_backend_ops.h b/include/hw/xen/xen_backend_ops.h
> index 90cca85f52..273e414559 100644
> --- a/include/hw/xen/xen_backend_ops.h
> +++ b/include/hw/xen/xen_backend_ops.h
> @@ -266,6 +266,8 @@ typedef uint32_t xs_transaction_t;
>   #define XS_PERM_READ  0x01
>   #define XS_PERM_WRITE 0x02
>   
> +#define XS_PRESERVE_OWNER        0xFFFE
> +
>   struct xenstore_backend_ops {
>       struct qemu_xs_handle *(*open)(void);
>       void (*close)(struct qemu_xs_handle *h);