>On Fri, Jul 26, 2013 at 8:48 AM, majianpeng <majianp...@gmail.com> wrote:
>>>On Thu, 25 Jul 2013, Yan, Zheng wrote:
>>>> On Thu, Jul 25, 2013 at 2:55 PM, majianpeng <majianp...@gmail.com> 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?
Thanks
Jianpeng Ma
>
>Regards
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