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Re: [Libguestfs] [PATCH nbdkit] cache, cow: Do not round size down.



On Wed, Feb 17, 2021 at 08:57:36AM -0600, Eric Blake wrote:
> Do you also want to tweak the sentence in nbdkit-truncate-filter.pod
> that mentions cache and cow filters?

Fixed in my copy.

> > +++ b/filters/cache/blk.c
> 
> >  int
> >  blk_set_size (uint64_t new_size)
> >  {
> > -  if (bitmap_resize (&bm, new_size) == -1)
> > +  size = new_size;
> > +
> > +  if (bitmap_resize (&bm, size) == -1)
> >      return -1;
> >  
> > -  if (ftruncate (fd, new_size) == -1) {
> > +  if (ftruncate (fd, ROUND_UP (size, blksize)) == -1) {
> 
> So the underlying fd is aligned...
> 
> >      nbdkit_error ("ftruncate: %m");
> >      return -1;
> >    }
> >  
> > -  if (lru_set_size (new_size) == -1)
> > +  if (lru_set_size (size) == -1)
> 
> ...while the lru size is still the original size.

My reading of the bitmap_resize function (which is also used by the
LRU code) is that rounds up, so we're OK here.  However the bitmap
code _is_ quite complicated ...

Well, the tests pass anyway :-)

Rich.

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