On Wed, 31 Jul 2013, majianpeng wrote:
> >On Tue, Jul 30, 2013 at 7:41 PM, majianpeng <majianpeng@xxxxxxxxx> wrote:
> >>>>
> >>>>>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
> >>>>>
> >>>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> >>>> index 2ddf061..22a98e5 100644
> >>>> --- a/fs/ceph/file.c
> >>>> +++ b/fs/ceph/file.c
> >>>> @@ -349,17 +349,17 @@ more:
> >>>> dout("striped_read %llu~%u (read %u) got %d%s%s\n", pos, left, read,
> >>>> ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
> >>>>
> >>>> - if (ret > 0) {
> >>>> - int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
> >>>> + if (ret >= 0) {
> >>>> + int didpages = (page_align + this_len) >> 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);
> >>>> + if (was_short) {
> >>>> + dout(" zero gap %llu to %llu\n", pos + ret, pos + this_len);
> >>>> + ceph_zero_page_vector_range(page_align + ret,
> >>>> + this_len - ret, pages);
> >>>> }
> >>>> - pos += ret;
> >>>> + pos += this_len;
> >>>> read = pos - off;
> >>>> - left -= ret;
> >>>> + left -= this_len;
> >>>> page_pos += didpages;
> >>>> pages_left -= didpages;
> >>>>
> >>>> This patch can do those case. It only add ret== 0 in judgement 'ret > 0".
> >>>
> >>>maybe we should add a i_size check. stop reading next strip object
> >>>when 'pos > i_size'
> >>>
> >> I think we can't do this because i_size may smaller than real size in ceph.
> >>
> >ceph_aio_read() calls ceph_do_getattr() when 'checkeof = true', it
> >handles the case.
> >
> >We must do i_size check in striped_read(), otherwise user program always gets as
> >much data as it requests. For example
> >
> >dd if=/dev/urandom bs=1M count=1 of=file_with_holes
> >dd if=file_with_holes bs=64M iflag=direct of=/dev/null
> >
> Before doing that, we must know the meaning of return value.
For ceph_osdc_readpages(),
> A: ret = ENOENT
The object does not exist.
> B: ret = 0
The object exists but we read 0 bytes, which means we are past EOF or the
object has size 0 bytes. Either way, we are either in a hole or past EOF.
sage
>
> Only we knowed this, we can handle exactly.
> Sage, can you explain those meaning in detail?
>
> Thanks!
> Jianpeng Ma
>
> >Regards
> >Yan, Zheng
> >
> >
> >>>> But i think i will add a parameter about hit_hole. It will make the code easy to understand.
> >>>>
> >>>
> >>> i think 'was_short' is equal to 'hit_hole'
> >>>
> >[snip]
> Thanks!
> Jianpeng Ma
> >On Tue, Jul 30, 2013 at 7:41 PM, majianpeng <majianpeng@xxxxxxxxx> wrote:
> >>>>
> >>>>>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
> >>>>>
> >>>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> >>>> index 2ddf061..22a98e5 100644
> >>>> --- a/fs/ceph/file.c
> >>>> +++ b/fs/ceph/file.c
> >>>> @@ -349,17 +349,17 @@ more:
> >>>> dout("striped_read %llu~%u (read %u) got %d%s%s\n", pos, left, read,
> >>>> ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
> >>>>
> >>>> - if (ret > 0) {
> >>>> - int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
> >>>> + if (ret >= 0) {
> >>>> + int didpages = (page_align + this_len) >> 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);
> >>>> + if (was_short) {
> >>>> + dout(" zero gap %llu to %llu\n", pos + ret, pos + this_len);
> >>>> + ceph_zero_page_vector_range(page_align + ret,
> >>>> + this_len - ret, pages);
> >>>> }
> >>>> - pos += ret;
> >>>> + pos += this_len;
> >>>> read = pos - off;
> >>>> - left -= ret;
> >>>> + left -= this_len;
> >>>> page_pos += didpages;
> >>>> pages_left -= didpages;
> >>>>
> >>>> This patch can do those case. It only add ret== 0 in judgement 'ret > 0".
> >>>
> >>>maybe we should add a i_size check. stop reading next strip object
> >>>when 'pos > i_size'
> >>>
> >> I think we can't do this because i_size may smaller than real size in ceph.
> >>
> >ceph_aio_read() calls ceph_do_getattr() when 'checkeof = true', it
> >handles the case.
> >
> >We must do i_size check in striped_read(), otherwise user program always gets as
> >much data as it requests. For example
> >
> >dd if=/dev/urandom bs=1M count=1 of=file_with_holes
> >dd if=file_with_holes bs=64M iflag=direct of=/dev/null
> >
> >Regards
> >Yan, Zheng
> >
> >
> >>>> But i think i will add a parameter about hit_hole. It will make the code easy to understand.
> >>>>
> >>>
> >>> i think 'was_short' is equal to 'hit_hole'
> >>>
> >[snip]
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