Re: [PATCH-for-5.1 1/2] tpm: Display when no backend is available

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> Display "No TPM backend available in this binary." error when
> no backend is available.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  tpm.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/tpm.c b/tpm.c
> index fe03b24858..e36803a64d 100644
> --- a/tpm.c
> +++ b/tpm.c
> @@ -41,6 +41,22 @@ tpm_be_find_by_type(enum TpmType type)
>      return TPM_BACKEND_CLASS(oc);
>  }
>  
> +/*
> + * Walk the list of available TPM backend drivers and count them.
> + */
> +static int tpm_backend_drivers_count(void)
> +{
> +    int count = 0, i;
> +
> +    for (i = 0; i < TPM_TYPE__MAX; i++) {
> +        const TPMBackendClass *bc = tpm_be_find_by_type(i);
> +        if (bc) {
> +            count++;
> +        }
> +    }
> +    return count;
> +}
> +
>  /*
>   * Walk the list of available TPM backend drivers and display them on the
>   * screen.
> @@ -87,6 +103,11 @@ static int tpm_init_tpmdev(void *dummy, QemuOpts *opts, 
> Error **errp)
>      TPMBackend *drv;
>      int i;
>  
> +    if (!tpm_backend_drivers_count()) {
> +        error_setg(errp, "No TPM backend available in this binary.");

Scratch the '.', please.  From error_setg()'s contract:

 * The resulting message should be a single phrase, with no newline or
 * trailing punctuation.

> +        return 1;
> +    }
> +
>      if (!QLIST_EMPTY(&tpm_backends)) {
>          error_setg(errp, "Only one TPM is allowed.");
>          return 1;

This works, but it's more code than I'd like to see for the purpose.

Moreover, it's tied to the error handling issue discussed in

    Subject: Re: What is TYPE_TPM_TIS_ISA? (Not an ISA Device)
    Message-ID: <87tuxyoauy.fsf@dusky.pond.sub.org>

If we revert flawed commit d10e05f15d5, then your patch needs a v2.
Your PATCH 2 might become unnecessary.  I'll give it a quick try to see
how it comes out.