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'
> 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.
Regards
Yan, Zheng
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