Re: [PATCH v6] iomap: support tail packing inline read

[Gao Xiang <hsiangkao@linux.alibaba.com>]

Hi Darrick,

On Thu, Jul 22, 2021 at 09:51:09AM -0700, Darrick J. Wong wrote:
> On Thu, Jul 22, 2021 at 07:39:47AM +0200, Christoph Hellwig wrote:
> > I think some of the language here is confusing - mostly about tail
> > packing when we otherwise use inline data.  Can you take a look at
> > the version below?  This mostly cleans up the terminology, adds a
> > new helper to check the size, and removes the error on trying to
> > write with a non-zero pos, as it can be trivially supported now.
> > 
> > ---
> > From 0f9c6ac6c2e372739b29195d25bebb8dd87e583a Mon Sep 17 00:00:00 2001
> > From: Gao Xiang <hsiangkao@linux.alibaba.com>
> > Date: Thu, 22 Jul 2021 11:17:29 +0800
> > Subject: iomap: make inline data support more flexible
> > 
> > Add support for offsets into the inline data page at iomap->inline_data
> > to cater for the EROFS tailpackng case where a small data is stored
> > right after the inode.
> 
> The commit message is a little misleading -- this adds support for
> inline data pages at nonzero (but page-aligned) file offsets, not file
> offsets into the page itself.  I suggest:
> 
> "Add support for reading inline data content into the page cache from
> nonzero page-aligned file offsets.  This enables the EROFS tailpacking
> mode where the last few bytes of the file are stored right after the
> inode."
> 
> The code changes look good to me.

Thanks for your suggestion. I've tested EROFS with no problem so far. 

I could update the commit message like this, what should I do next?

Many thanks,
Gao Xiang

> 
> --D
> 
> > 
> > Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
> > ---
> >  fs/iomap/buffered-io.c | 35 ++++++++++++++++++-----------------
> >  fs/iomap/direct-io.c   | 10 ++++++----
> >  include/linux/iomap.h  | 14 ++++++++++++++
> >  3 files changed, 38 insertions(+), 21 deletions(-)
> > 
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 87ccb3438becd9..0597f5c186a33f 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -205,25 +205,29 @@ struct iomap_readpage_ctx {
> >  	struct readahead_control *rac;
> >  };
> >  
> > -static void
> > -iomap_read_inline_data(struct inode *inode, struct page *page,
> > -		struct iomap *iomap)
> > +static int iomap_read_inline_data(struct inode *inode, struct page *page,
> > +		struct iomap *iomap, loff_t pos)
> >  {
> > -	size_t size = i_size_read(inode);
> > +	size_t size = iomap->length + iomap->offset - pos;
> >  	void *addr;
> >  
> >  	if (PageUptodate(page))
> > -		return;
> > +		return PAGE_SIZE;
> >  
> > -	BUG_ON(page_has_private(page));
> > -	BUG_ON(page->index);
> > -	BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> > +	/* inline data must start page aligned in the file */
> > +	if (WARN_ON_ONCE(offset_in_page(pos)))
> > +		return -EIO;
> > +	if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
> > +		return -EIO;
> > +	if (WARN_ON_ONCE(page_has_private(page)))
> > +		return -EIO;
> >  
> >  	addr = kmap_atomic(page);
> > -	memcpy(addr, iomap->inline_data, size);
> > +	memcpy(addr, iomap_inline_buf(iomap, pos), size);
> >  	memset(addr + size, 0, PAGE_SIZE - size);
> >  	kunmap_atomic(addr);
> >  	SetPageUptodate(page);
> > +	return PAGE_SIZE;
> >  }
> >  
> >  static inline bool iomap_block_needs_zeroing(struct inode *inode,
> > @@ -246,11 +250,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> >  	unsigned poff, plen;
> >  	sector_t sector;
> >  
> > -	if (iomap->type == IOMAP_INLINE) {
> > -		WARN_ON_ONCE(pos);
> > -		iomap_read_inline_data(inode, page, iomap);
> > -		return PAGE_SIZE;
> > -	}
> > +	if (iomap->type == IOMAP_INLINE)
> > +		return iomap_read_inline_data(inode, page, iomap, pos);
> >  
> >  	/* zero post-eof blocks as the page may be mapped */
> >  	iop = iomap_page_create(inode, page);
> > @@ -618,14 +619,14 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
> >  	}
> >  
> >  	if (srcmap->type == IOMAP_INLINE)
> > -		iomap_read_inline_data(inode, page, srcmap);
> > +		status = iomap_read_inline_data(inode, page, srcmap, pos);
> >  	else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
> >  		status = __block_write_begin_int(page, pos, len, NULL, srcmap);
> >  	else
> >  		status = __iomap_write_begin(inode, pos, len, flags, page,
> >  				srcmap);
> >  
> > -	if (unlikely(status))
> > +	if (unlikely(status < 0))
> >  		goto out_unlock;
> >  
> >  	*pagep = page;
> > @@ -675,7 +676,7 @@ static size_t iomap_write_end_inline(struct inode *inode, struct page *page,
> >  
> >  	flush_dcache_page(page);
> >  	addr = kmap_atomic(page);
> > -	memcpy(iomap->inline_data + pos, addr + pos, copied);
> > +	memcpy(iomap_inline_buf(iomap, pos), addr + pos, copied);
> >  	kunmap_atomic(addr);
> >  
> >  	mark_inode_dirty(inode);
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index 9398b8c31323b3..a6aaea2764a55f 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -378,23 +378,25 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
> >  		struct iomap_dio *dio, struct iomap *iomap)
> >  {
> >  	struct iov_iter *iter = dio->submit.iter;
> > +	void *dst = iomap_inline_buf(iomap, pos);
> >  	size_t copied;
> >  
> > -	BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
> > +	if (WARN_ON_ONCE(!iomap_inline_data_size_valid(iomap)))
> > +		return -EIO;
> >  
> >  	if (dio->flags & IOMAP_DIO_WRITE) {
> >  		loff_t size = inode->i_size;
> >  
> >  		if (pos > size)
> > -			memset(iomap->inline_data + size, 0, pos - size);
> > -		copied = copy_from_iter(iomap->inline_data + pos, length, iter);
> > +			memset(iomap_inline_buf(iomap, size), 0, pos - size);
> > +		copied = copy_from_iter(dst, length, iter);
> >  		if (copied) {
> >  			if (pos + copied > size)
> >  				i_size_write(inode, pos + copied);
> >  			mark_inode_dirty(inode);
> >  		}
> >  	} else {
> > -		copied = copy_to_iter(iomap->inline_data + pos, length, iter);
> > +		copied = copy_to_iter(dst, length, iter);
> >  	}
> >  	dio->size += copied;
> >  	return copied;
> > diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> > index 479c1da3e2211e..5efae7153912ed 100644
> > --- a/include/linux/iomap.h
> > +++ b/include/linux/iomap.h
> > @@ -97,6 +97,20 @@ iomap_sector(struct iomap *iomap, loff_t pos)
> >  	return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
> >  }
> >  
> > +static inline void *iomap_inline_buf(const struct iomap *iomap, loff_t pos)
> > +{
> > +	return iomap->inline_data - iomap->offset + pos;
> > +}
> > +
> > +/*
> > + * iomap->inline_data is a potentially kmapped page, ensure it never crosseѕ a
> > + * page boundary.
> > + */
> > +static inline bool iomap_inline_data_size_valid(const struct iomap *iomap)
> > +{
> > +	return iomap->length <= PAGE_SIZE - offset_in_page(iomap->inline_data);
> > +}
> > +
> >  /*
> >   * When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
> >   * and page_done will be called for each page written to.  This only applies to
> > -- 
> > 2.30.2
> >