On Fri, Jul 26, 2013 at 9:38 AM, majianpeng <majianpeng@xxxxxxxxx> wrote:
>>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.
> The reason cause short-read is only EOF? or other reason?
>
I think yes, (at least for reading from FS and read size is not very large)
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