On Fri, Jul 26, 2013 at 9:22 AM, majianpeng <majianpeng@xxxxxxxxx> wrote:
>>On Fri, Jul 26, 2013 at 8:48 AM, majianpeng <majianpeng@xxxxxxxxx> wrote:
>>>>On Thu, 25 Jul 2013, Yan, Zheng wrote:
>>>>> On Thu, Jul 25, 2013 at 2:55 PM, majianpeng <majianpeng@xxxxxxxxx> wrote:
>>>>> >>On Thu, 25 Jul 2013, majianpeng wrote:
>>>>> >>> Hi all,
>>>>> >>> I met a problem and ask somebody could help me.
>>>>> >>> In func striped_read()
>>>>> >>> > if (ret > 0) {
>>>>> >>> > int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
>>>>> >>>
>>>>> >>> > if (read < pos - off) {
>>>>> >>> > dout(" zero gap %llu to %llu\n", off + read, pos);
>>>>> >>> > ceph_zero_page_vector_range(page_align + read,
>>>>> >>> > pos - off - read, pages);
>>>>> >>> > }
>>>>> >>> > pos += ret;
>>>>>
>>>>> I think you are right. probably above line should be 'pos += this_len'
>>>>
>>>>It should be easy to construct a simple test for this. E.g., something
>>>>like
>>>>
>>>> pwrite(fd, buf, 0, 3000000);
>>>> pwrite(fd, buf, 4194304, 1000);
>>>> pread(fd, buf, 0, 6000000);
>>>> ...
>>>>
>>>>and whatever else to verify that pos was in fact advanced properly?
>>>>
>>> The following is my test code:
>>> void hole_test()
>>> {
>>> char buf[4194304];
>>> ssize_t ret;
>>> int fd = open("/media/ceph/test", O_RDWR|O_CREAT|O_DIRECT|O_TRUNC);
>>> if (fd < 0) {
>>> printf("open error %s\n", strerror(errno));
>>> return;
>>> }
>>>
>>> ret = pwrite(fd, buf, 0, 3000000);
>>> ret = pwrite(fd, buf, 4194304, 1000);
>>> ret = pread(fd, buf , 0, 6000000);
>>> close(fd);
>>> }
>>>
>>> The debug message from striped_read are:
>>> [ 267.530266] ceph: file.c:356 : striped_read 6000000~0 (read 0) got 0
>>> [ 267.530270] ceph: file.c:396 : striped_read returns 0
>>>
>>> The result isn't what's your said.
>>> Am i missing something?
>>>
>>> BTW, i think Yan is ok,
>>> The code
>>> pos += ret; should pos += this_len.
>>> Because this_len can larger than ret.
>>> But the question is what's condition can cause this?
>>
>>by default, ceph strips file to 4M objects. In above example, the
>>first object only has
>>3M data, so 'ret = 3M' and 'this_len = 4M'
> actually, in func calc_layout: the read length is the smaller between object and left.
>>
>>> And can the short_read operation handle this situation?
>>
>>I don't think it's good idea to short read unless we really reach EOF.
> Can you explain in detail?
>
because some user program interpret short read as EOF reached. If we
return short
read they get confused.
Regards
Yan, Zheng
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