Re: [PATCH v2 17/18] modules: check arch and block load on mismatch

[Claudio Fontana]

On 6/10/21 2:35 PM, Daniel P. Berrangé wrote:
> On Thu, Jun 10, 2021 at 07:57:54AM +0200, Gerd Hoffmann wrote:
>> Add module_allow_arch() to set the target architecture.
>> In case a module is limited to some arch verify arches
>> match and ignore the module if not.
>>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>> ---
>>  include/qemu/module.h |  1 +
>>  softmmu/vl.c          |  3 +++
>>  util/module.c         | 15 +++++++++++++++
>>  3 files changed, 19 insertions(+)
>>
>> diff --git a/include/qemu/module.h b/include/qemu/module.h
>> index d3cab3c25a2f..7825f6d8c847 100644
>> --- a/include/qemu/module.h
>> +++ b/include/qemu/module.h
>> @@ -72,6 +72,7 @@ void module_call_init(module_init_type type);
>>  bool module_load_one(const char *prefix, const char *lib_name, bool 
>> mayfail);
>>  void module_load_qom_one(const char *type);
>>  void module_load_qom_all(void);
>> +void module_allow_arch(const char *arch);
>>  
>>  /*
>>   * macros to store module metadata in a .modinfo section.
>> diff --git a/softmmu/vl.c b/softmmu/vl.c
>> index ba26a042b284..96316774fcc9 100644
>> --- a/softmmu/vl.c
>> +++ b/softmmu/vl.c
>> @@ -126,6 +126,8 @@
>>  #include "sysemu/iothread.h"
>>  #include "qemu/guest-random.h"
>>  
>> +#include "config-host.h"
>> +
>>  #define MAX_VIRTIO_CONSOLES 1
>>  
>>  typedef struct BlockdevOptionsQueueEntry {
>> @@ -2723,6 +2725,7 @@ void qemu_init(int argc, char **argv, char **envp)
>>      error_init(argv[0]);
>>      qemu_init_exec_dir(argv[0]);
>>  
>> +    module_allow_arch(TARGET_NAME);
>>      qemu_init_subsystems();
>>  
>>      /* first pass of option parsing */
>> diff --git a/util/module.c b/util/module.c
>> index 6e4199169c41..564b8e3da760 100644
>> --- a/util/module.c
>> +++ b/util/module.c
>> @@ -122,6 +122,12 @@ void module_call_init(module_init_type type)
>>  static Modules *modinfo;
>>  static char *module_dirs[5];
>>  static int module_ndirs;
>> +static const char *module_arch;
>> +
>> +void module_allow_arch(const char *arch)
>> +{
>> +    module_arch = arch;
>> +}
>>  
>>  static void module_load_path_init(void)
>>  {
>> @@ -295,6 +301,14 @@ bool module_load_one(const char *prefix, const char 
>> *lib_name, bool mayfail)
>>      module_load_modinfo();
>>  
>>      for (modlist = modinfo->list; modlist != NULL; modlist = modlist->next) 
>> {
>> +        if (modlist->value->has_arch) {
>> +            if (strcmp(modlist->value->name, module_name) == 0) {
>> +                if (!module_arch ||
>> +                    strcmp(modlist->value->arch, module_arch) != 0) {
>> +                    return false;
>> +                }
>> +            }
>> +        }
> 
> I have a little hard time following the code paths, but IIUC, with this
> change, instead of "module.so" we would have multiple copies of something
> like "module-$arch.so" ?  Then we load them all, read their modinfo section
> and discard the ones with non-matching arch ?
> 
> If that is a correct understanding, then I wonder about the scalability of
> it. We have 30 system emulator targets right now, so if we get even a few
> arch specific modues, that's going to be alot of modules we're loading,
> checking and discarding.
> 
> Wouldn't it be simpler if we just made use of the directory layout
> /usr/lib64/qemu/$mod.so for common modules and /usr/lib64/qemu/$arch/$mod.so
> for arch specific modules. That would let us load only the modules we know
> are applicable for the system target arch and not need this post-load
> filtering from metadata.
> 
> Regards,
> Daniel
> 

agreed.

Claudio