Re: [RFC PATCH 8/8] tpm: Move backend code under the 'backends/' directory

[Thomas Huth <thuth@redhat.com>]

On 11/06/2020 14.00, Stefan Berger wrote:
> On 6/10/20 4:02 PM, Philippe Mathieu-Daudé wrote:
>> TPM subsytem is split into backends (see commit f4ede81eed2)
>> and frontends (see i.e. 3676bc69b35). Keep the emulated
>> hardware 'frontends' under hw/tpm/, but move the backends
>> in the backends/ directory.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>> RFC due to a FIXME in tpm_tis_common.c, it uses
>> TRACE_TPM_UTIL_SHOW_BUFFER which is now generated
>> by backends/trace-events...
>> ---
>>   Makefile                               |  2 +-
>>   {hw/tpm => backends}/tpm_int.h         |  6 ++---
>>   {hw/tpm => backends}/tpm_ioctl.h       |  0
>>   {hw/tpm => backends}/tpm_emulator.c    |  0
>>   {hw/tpm => backends}/tpm_passthrough.c |  0
>>   {hw/tpm => backends}/tpm_util.c        |  0
> 
> I don't understand this move. Why not keep everything TPM related in one
> directory even though there may be a backend directory where 'nothing
> else fits but the name.' All we need to remember is that 'emulator' and
> 'passthrough' are the backends.

We try to have a clean separation between frontends and backends in
QEMU. The concepts have been mixed in the past (see e.g. the -drive
parameter) and that led only to confusion and trouble later. The hw/
directory is clearly for emulated hardware device frontends only, we
should not include any backend code here.

 Thomas