On 14:36 Срд 13 Июн , Hugh Dickins wrote:
> On Wed, 13 Jun 2007, Dmitriy Monakhov wrote:
>
> > loop.c code itself is not perfect. In fact before Nick's patch
> > partial write was't possible. Assumption what write chunks are
> > always page aligned is realy weird ( see "index++" line).
> >
> > Signed-off-by: Dmitriy Monakhov <[email protected]>
>
> I'm interested, because I'm trying to chase down an -mm bug which
> occasionally leaves me with 1k of zeroes where it shouldn't (in a
> 1k bsize ext2 looped over tmpfs). The length of time for this to
> happen varies a lot, so bisection has been misleading: maybe the
> problem lies in Nick's patches, maybe it does not.
>
> But I don't understand your fix below at all. _If_ you need to
> change the handling of index, then you need to change the handling
> of offset too, don't you?
>
> But what's wrong with how inded was handled anyway? Yes, it might
> be being incremented at the bottom of the loop when we haven't
> reached the end of this page, but in that case we're not going
> round the loop again anyway: len will now be 0. So no problem.
>
> One of us is missing something: please enlighten me - thanks.
Yepp. You absolutely right, wrong patch was attached :(
Btw: Nick's patches broke LO_CRYPT_XOR mode, but it is ok because
this feature was absolete and not used by anyone, am i right here?
>
> Hugh
>
> >
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index 4bab9b1..8726da5 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -215,7 +215,6 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
> > int len, ret;
> >
> > mutex_lock(&mapping->host->i_mutex);
> > - index = pos >> PAGE_CACHE_SHIFT;
> > offset = pos & ((pgoff_t)PAGE_CACHE_SIZE - 1);
> > bv_offs = bvec->bv_offset;
> > len = bvec->bv_len;
> > @@ -226,6 +225,7 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
> > struct page *page;
> > void *fsdata;
> >
> > + index = pos >> PAGE_CACHE_SHIFT;
> > IV = ((sector_t)index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);
> > size = PAGE_CACHE_SIZE - offset;
> > if (size > len)
> > @@ -255,7 +255,6 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
> > bv_offs += copied;
> > len -= copied;
> > offset = 0;
> > - index++;
> > pos += copied;
> > }
> > ret = 0;
> -
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