Re: [Qemu-devel] [PATCH 1/4] migration: set f->is_write and flush in add_to_iovec

[Paolo Bonzini <pbonzini@redhat.com>]

Il 09/04/2013 13:32, Juan Quintela ha scritto:
> Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  savevm.c | 25 +++++++++----------------
>>  1 file changed, 9 insertions(+), 16 deletions(-)
>>
>> diff --git a/savevm.c b/savevm.c
>> index b1d8988..c952c41 100644
>> --- a/savevm.c
>> +++ b/savevm.c
>> @@ -631,6 +631,11 @@ static void add_to_iovec(QEMUFile *f, const uint8_t *buf, int size)
>>          f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
>>          f->iov[f->iovcnt++].iov_len = size;
>>      }
>> +
>> +    f->is_write = 1;
>> +    if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
>> +        qemu_fflush(f);
>> +    }
>>  }
>>  
>>  void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, int size)
>> @@ -645,14 +650,8 @@ void qemu_put_buffer_async(QEMUFile *f, const uint8_t *buf, int size)
>>          abort();
>>      }
>>  
>> -    add_to_iovec(f, buf, size);
>> -
>> -    f->is_write = 1;
>>      f->bytes_xfer += size;
>> -
>> -    if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
>> -        qemu_fflush(f);
>> -    }
>> +    add_to_iovec(f, buf, size);
>>  }
>>  
>>  void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size)
>> @@ -674,7 +673,6 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size)
>>          if (l > size)
>>              l = size;
>>          memcpy(f->buf + f->buf_index, buf, l);
>> -        f->is_write = 1;
>>          f->buf_index += l;
> 
> we increase buf_index
> 
>>          qemu_put_buffer_async(f, f->buf + (f->buf_index - l), l);
> 
> and we call add_to_iovec() here inside.  Notice the torture to get the
> old buf_index value.
> 
>>          if (qemu_file_get_error(f)) {
>> @@ -697,15 +695,10 @@ void qemu_put_byte(QEMUFile *f, int v)
>>          abort();
>>      }
>>  
>> -    f->buf[f->buf_index++] = v;
>> -    f->is_write = 1;
>> +    f->buf[f->buf_index] = v;
>>      f->bytes_xfer++;
>> -
>> -    add_to_iovec(f, f->buf + (f->buf_index - 1), 1);
>> -
>> -    if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
>> -        qemu_fflush(f);
>> -    }
>> +    add_to_iovec(f, f->buf + f->buf_index, 1);
>> +    f->buf_index++;
> 
> And here,  we call add_to_iovec() and then increase buf_index
> 
> Is there any good reason for not being consistent?

The reason is that I didn't want to switch
qemu_put_buffer_async->add_to_iovec in this patch.  I do it in the next one.

> Once there,  I think that moving the handling of buf_index to inside
> add_to_iovec() looks like a good idea?

add_to_iovec() is not called always with something from f->buf.  But it
is a good idea to move this handling of buf_index:

    if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {

out of add_to_iovec.  I do that in patch 4.

Paolo