Re: [PATCH] generic/465: fix a read bug when encounter EOF

[Su Yanjun <suyj.fnst@cn.fujitsu.com>]

在 2019/9/25 17:47, Eryu Guan 写道:
> On Mon, Sep 16, 2019 at 01:24:26PM +0800, Su Yanjun wrote:
>> In nfs test, if the writer has not written enough data for reader reading,
>> then reader only get partial data and test fails.
>>
>> We can continue reading until read enough data.
>>
>> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
> Would you please provide more info on the actual failure you've seen? I
> think the partial read issue should have been addressed by commit
> 2428c08a6025 ("generic/465: just check the actual read data under dio
> read/write")

I rechecked my patch and my patch is not needed at all.

It's  only workaround of a kernel bug of nfs. In some cases nfs returns 
wrong data to userspace, but the return value is ok.

I will send a kernel patch to nfs mailist.

Thanks a lot.

>
> Thanks,
> Eryu
>
>> ---
>>   src/aio-dio-regress/aio-dio-append-write-read-race.c | 17 +++++++++++++++--
>>   1 file changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/aio-dio-regress/aio-dio-append-write-read-race.c b/src/aio-dio-regress/aio-dio-append-write-read-race.c
>> index 911f272..f28ef3c 100644
>> --- a/src/aio-dio-regress/aio-dio-append-write-read-race.c
>> +++ b/src/aio-dio-regress/aio-dio-append-write-read-race.c
>> @@ -44,14 +44,27 @@ static void usage(const char *prog)
>>   static void *reader(void *arg)
>>   {
>>   	struct io_data *data = (struct io_data *)arg;
>> +	size_t blksize = data->blksize;
>> +	size_t offset = data->offset;
>> +	char   *buf = data->buf;
>>   
>>   	memset(data->buf, 'b', data->blksize);
>>   	reader_ready = 1;
>>   	do {
>> -		data->read_sz = pread(data->fd, data->buf, data->blksize,
>> -				      data->offset);
>> +		data->read_sz = pread(data->fd, buf, blksize,
>> +				      offset);
>>   		if (data->read_sz < 0)
>>   			perror("read file");
>> +
>> +		if (data->read_sz > 0) {
>> +			blksize -= data->read_sz;
>> +			offset  += data->read_sz;
>> +			buf	+= data->read_sz;
>> +			data->read_sz = 0;
>> +		}
>> +
>> +		if (blksize <= 0)
>> +			break;
>>   	} while (data->read_sz <= 0);
>>   
>>   	return NULL;
>> -- 
>> 2.7.4
>>
>>
>>
>