Re: [Qemu-devel] [PATCH qom-cpu v3 9/9] memory_mapping: Change qemu_get_guest_memory_mapping() semantics

["Andreas Färber" <afaerber@suse.de>]

Am 31.05.2013 16:14, schrieb Luiz Capitulino:
> On Thu, 30 May 2013 17:08:01 +0200
> Andreas Färber <afaerber@suse.de> wrote:
> 
>> Previously it would search for the first CPU with paging enabled and
>> retrieve memory mappings from this and any following CPUs or return an
>> error if that fails.
>>
>> Instead walk all CPUs and if paging is enabled retrieve the memory
>> mappings. Fail only if retrieving memory mappings on a CPU with paging
>> enabled fails.
>>
>> This not only allows to more easily use one qemu_for_each_cpu() instead
>> of open-coding two CPU loops and drops find_first_paging_enabled_cpu()
>> but removes the implicit assumption of heterogeneity between CPUs n..N
>> in having paging enabled.
>>
>> Cc: Wen Congyang <wency@cn.fujitsu.com>
>> Signed-off-by: Andreas Färber <afaerber@suse.de>
>> ---
>>  memory_mapping.c | 42 +++++++++++++++++++++++-------------------
>>  1 file changed, 23 insertions(+), 19 deletions(-)
>>
>> diff --git a/memory_mapping.c b/memory_mapping.c
>> index 481530a..55ac2b8 100644
>> --- a/memory_mapping.c
>> +++ b/memory_mapping.c
>> @@ -165,35 +165,39 @@ void memory_mapping_list_init(MemoryMappingList *list)
>>      QTAILQ_INIT(&list->head);
>>  }
>>  
>> -static CPUArchState *find_paging_enabled_cpu(CPUArchState *start_cpu)
>> +typedef struct GetGuestMemoryMappingData {
>> +    MemoryMappingList *list;
>> +    int ret;
>> +} GetGuestMemoryMappingData;
>> +
>> +static void qemu_get_one_guest_memory_mapping(CPUState *cpu, void *data)
>>  {
>> -    CPUArchState *env;
>> +    GetGuestMemoryMappingData *s = data;
>> +    int ret;
>>  
>> -    for (env = start_cpu; env != NULL; env = env->next_cpu) {
>> -        if (cpu_paging_enabled(ENV_GET_CPU(env))) {
>> -            return env;
>> -        }
>> +    if (!cpu_paging_enabled(cpu) || s->ret == -1) {
>> +        return;
>> +    }
>> +    ret = cpu_get_memory_mapping(cpu, s->list);
>> +    if (ret < 0) {
>> +        s->ret = -1;
>> +    } else {
>> +        s->ret = 0;
>>      }
> 
> Does cpu_get_memory_mapping() ever return a positive value or a negative
> value != -1 ?
> 
> It it doesn't, I'd do:
> 
> s->ret = cpu_get_memory_mapping();
> assert(s->ret == 0 || s->ret == -1);

This no longer applies after returning an Error* from
cpu_get_memory_mapping() instead. :)

> 
>> -
>> -    return NULL;
>>  }
>>  
>>  int qemu_get_guest_memory_mapping(MemoryMappingList *list)
>>  {
>> -    CPUArchState *env, *first_paging_enabled_cpu;
>> +    GetGuestMemoryMappingData s = {
>> +        .list = list,
>> +        .ret = -2,
>> +    };
>>      RAMBlock *block;
>>      ram_addr_t offset, length;
>> -    int ret;
>>  
>> -    first_paging_enabled_cpu = find_paging_enabled_cpu(first_cpu);
>> -    if (first_paging_enabled_cpu) {
>> -        for (env = first_paging_enabled_cpu; env != NULL; env = env->next_cpu) {
>> -            ret = cpu_get_memory_mapping(ENV_GET_CPU(env), list);
>> -            if (ret < 0) {
>> -                return -1;
>> -            }
>> -        }
>> -        return 0;
>> +    qemu_for_each_cpu(qemu_get_one_guest_memory_mapping, &s);
>> +    if (s.ret != -2) {
>> +        return s.ret;
>>      }
> 
> I see we ignore error in dump_init(). Doesn't matter today because
> x86_cpu_get_memory_mapping() never fails. But as you're doing this cleanup,
> shouldn't you add proper error handling?

This patch is not needed for arm/s390x, so we can easily postpone it. I
included it here for early feedback since my series building on this
still needs to be tested and tweaked for bsd-user.

I figure passing through Error** would be the logical follow-up here?
Yet s.ret is being reused to check if any CPU provided any mappings at
all - we could instead do two loops, one for checking if any CPU has
paging enabled and then one passing out any Error* and propagating that.

Thanks,
Andreas

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