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'
regards
yan, zheng
>>> > read = pos - off;
>>>
>>> At first , pos = off and off don't modify.
>>> Why does it judge 'read < pos -off ' ?
>>> Because the read = pos -off, so the read must equal pos -off.
>>
>>This block triggers if we hit a stripe. off is always the original
>>starting offset. pos is the current position that we just tried to read
>>from. We might:
>>
>> - try to read a big extent from off == pos
>> - readpages truncates this to the end of the object
>> - we get a short read (not a complete object)
> What's the mean of not a complete object?
> FYI,a short read maybe met the boundry of stripe(object) or the EOF of file.
> For the hole of file, i don't know how to handle.
>> - read is some partial amount
>> - pos is off + read + a gap
> From the code : read = pos - off; after that, the pos don't change.
> So the a gap where is from?
>
> Thanks!
> Jianpeng Ma
>> - we try to read from the next object and there is data
>> => there was a hole and we need to zero the gap
>>
>>If, on the other hand, there isn't data in the next object, then we don't
>>want to zero the hole.. and least not until we decide where EOF is.
>>That's why this block is where it is, and never triggers on the first
>>iteration.
>>
>>Does that make sense?
>>sage
--
To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
