Re: [Virtio-fs] [PATCH v4 2/2] virtiofsd: use fuse_buf_writev to replace fuse_buf_write for better performance

[piaojun <piaojun@huawei.com>]

Hi Stefan,

On 2019/8/14 20:52, Stefan Hajnoczi wrote:
> On Fri, Aug 09, 2019 at 08:53:20AM +0800, piaojun wrote:
>> diff --git a/contrib/virtiofsd/buffer.c b/contrib/virtiofsd/buffer.c
>> index cec762f..d127c45 100644
>> --- a/contrib/virtiofsd/buffer.c
>> +++ b/contrib/virtiofsd/buffer.c
>> @@ -318,11 +318,22 @@ static int fuse_bufvec_advance(struct fuse_bufvec *bufv, size_t len)
>>  ssize_t fuse_buf_copy(fuse_req_t req, struct fuse_bufvec *dstv, struct fuse_bufvec *srcv,
>>  		      enum fuse_buf_copy_flags flags)
>>  {
>> +	size_t i;
>>  	size_t copied = 0;
>>
>>  	if (dstv == srcv)
>>  		return fuse_buf_size(dstv);
>>
>> +	/* use writev to improve bandwidth when all the
>> +	 * src buffers already mapped by the daemon
>> +	 * process */
> 
> Some more checks to make this generic:
> 
>> +	for (i = 0; i < srcv->count; i++) {
>> +		if (srcv->buf[i].flags & FUSE_BUF_PHYS_ADDR)
>> +			break;
> 
>                 if (srcv->buf[i].flags & FUSE_BUF_IS_FD)
> 		        break;
> 
>> +	}
>> +	if (i == srcv->count)
> 
> Please verify the preconditions for the destination buffer too:
> 
>   && dstv->count == 1 && dstv->idx == 0 && dstv->off == 0 &&
>   (dstv->buf[0].flags & FUSE_BUF_IS_FD)

Thanks for your comments, and I prefer adding checker just for
FUSE_BUF_IS_FD as fuse_buf_writev() does not care much about the other
parts. And I personally think so many preconditions will make
fuse_buf_writev() so specific.

Thanks,
Jun

> 
>> +		return fuse_buf_writev(req, &dstv->buf[0], srcv);