On Tue, Jul 30, 2013 at 10:08 AM, majianpeng <majianpeng@xxxxxxxxx> wrote: >>On Mon, Jul 29, 2013 at 11:00 AM, majianpeng <majianpeng@xxxxxxxxx> wrote: >>> >>> [snip] >>> >I don't think the later was_short can handle the hole case. For the hole case, >>> >we should try reading next strip object instead of return. how about >>> >below patch. >>> > >>> Hi Yan, >>> i uesed this demo to test hole case. >>> dd if=/dev/urandom bs=4096 count=2 of=file_with_holes >>> dd if=/dev/urandom bs=4096 seek=7 count=2 of=file_with_holes >>> >>> dd if=file_with_holes of=/dev/null bs=16k count=1 iflag=direct >>> Using the dynamic_debug in striped_read, the message are: >>> >[ 8743.663499] ceph: file.c:350 : striped_read 0~16384 (read 0) got 16384 >>> >[ 8743.663502] ceph: file.c:390 : striped_read returns 16384 >>> From the messages, we can see it can't hit the short-read. >>> For the ceph-file-hole, how does the ceph handle? >>> Or am i missing something? >> >>the default strip size is 4M, all data are written to the first object >>in your test case. >>could you try something like below. >> >>dd if=/dev/urandom bs=1M count=2 of=file_with_holes >>dd if=/dev/urandom bs=1M count=2 seek=4 of=file_with_holes conv=notrunc >>dd if=file_with_holes bs=8M >/dev/null >> > > From above test, i think your patch is right. > Although, the original code can work but it call multi striped_read. For test case --- dd if=/dev/urandom bs=1M count=2 of=file_with_holes dd if=/dev/urandom bs=1M count=2 seek=4 of=file_with_holes conv=notrunc dd if=file_with_holes bs=8M iflag=direct >/dev/null I got --- ceph: striped_read 0~8388608 (read 0) got 2097152 HITSTRIPE SHORT ceph: striped_read 2097152~6291456 (read 2097152) got 0 HITSTRIPE SHORT ceph: zero tail 4194304 ceph: striped_read returns 6291456 ceph: sync_read result 6291456 ceph: aio_read ffff88000fb22f98 10000193e8c.fffffffffffffffe dropping cap refs on Fcr = 6291456 the original code zeros data in range 2M~6M, it's obvious incorrect. > As your said for stripe short-read,it doesn't make sense to return rather than reading next stripe. > But can you add some comments for this? > The short-read reasongs are two:EOF or hit-hole. > But for hit-hole there are some differents case. For that i don't know. > For hit-hole, there is only one case: the strip object's size is smaller then 4M. When reading a strip object, if the returned data is less than we expected, we need to check if following strip objects have data. I think the original code and my patch doesn't handle the below case properly. | object 0 | hole | hole | object 3 | dd if=testfile iflag=direct bs=16M >/dev/null Could you write a patch, do some tests and submit it. Regards Yan, Zheng -- 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
