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Date: Sat, 24 Jul 2021 15:52:20 +0800
From: Gao Xiang <hsiangkao@linux.alibaba.com>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: Re: [PATCH 2/2] iomap: Support inline data with block size < page size
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On Sat, Jul 24, 2021 at 01:11:09PM +0800, Gao Xiang wrote:
> On Sat, Jul 24, 2021 at 12:46:45PM +0800, Gao Xiang wrote:

...

> > 
> > Thanks for the patch!
> > 
> > Previously I'd like to skip the leading uptodate blocks and update the
> > extent it covers that is due to already exist iop. If we get rid of the
> > offset_in_page(pos) restriction like this, I'm not sure if we (or some
> > other fs users) could face something like below (due to somewhat buggy
> > fs users likewise):
> > 
> >  [0 - 4096)    plain block
> > 
> >  [4096 - 4608)  tail INLINE 1 (e.g. by mistake or just splitted
> >                                     .iomap_begin() report.)
> >  [4608 - 5120]  tail INLINE 2
> > 
> 
> (cont.)
> 
> So I think without the !offset_in_page(pos) restriction, at least we
> may need to add something like:
> 
> if (WARN_ON_ONCE(size != i_size_read(inode) - iomap->offset))
> 	return -EIO;
> 
> to the approach to detect such cases at least but that is no need with
> page-sized and !offset_in_page(pos) restriction.
> 

Never mind, after rethinking with clear head, I think I was overthinking
this part and it shouldn't behave like this. Sorry about the noise above.

> > 
> > >  
> > > -	addr = kmap_atomic(page);
> > > +	addr = kmap_atomic(page) + poff;
> > >  	memcpy(addr, iomap_inline_buf(iomap, pos), size);
> > > -	memset(addr + size, 0, PAGE_SIZE - size);
> > > +	memset(addr + size, 0, PAGE_SIZE - poff - size);
> > >  	kunmap_atomic(addr);
> > 
> > As my limited understanding, this may need to be fixed, since it
> > doesn't match kmap_atomic(page)...
> > 
> > Thanks,
> > Gao Xiang
> > 
> > > -	SetPageUptodate(page);
> > > -	return PAGE_SIZE;
> > > +	iomap_set_range_uptodate(page, poff, PAGE_SIZE - poff);
> > > +	return PAGE_SIZE - poff;
> > >  }
> > >  
> > >  static inline bool iomap_block_needs_zeroing(struct inode *inode,
> > > -- 
> > > 2.30.2
> > >