linux-kernel - Re: [PATCH v3 11/13] bcachefs: fiemap: return correct extent physical length

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Date: Wed, 3 Apr 2024 14:15:21 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Brian Foster <bfoster@...hat.com>
Cc: Sweet Tea Dorminy <sweettea-kernel@...miny.me>, 
	Jonathan Corbet <corbet@....net>, Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>, 
	David Sterba <dsterba@...e.com>, Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Mickaël Salaün <mic@...ikod.net>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-bcachefs@...r.kernel.org, linux-btrfs@...r.kernel.org, 
	linux-f2fs-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v3 11/13] bcachefs: fiemap: return correct extent
 physical length

On Wed, Apr 03, 2024 at 01:00:11PM -0400, Brian Foster wrote:
> On Wed, Apr 03, 2024 at 03:22:52AM -0400, Sweet Tea Dorminy wrote:
> > Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@...miny.me>
> > ---
> >  fs/bcachefs/fs.c | 18 ++++++++++++------
> >  1 file changed, 12 insertions(+), 6 deletions(-)
> > 
> > diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c
> > index f830578a9cd1..d2793bae842d 100644
> > --- a/fs/bcachefs/fs.c
> > +++ b/fs/bcachefs/fs.c
> > @@ -913,15 +913,17 @@ static int bch2_fill_extent(struct bch_fs *c,
> >  			flags |= FIEMAP_EXTENT_SHARED;
> >  
> >  		bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
> > -			int flags2 = 0;
> > +			int flags2 = FIEMAP_EXTENT_HAS_PHYS_LEN;
> > +			u64 phys_len = k.k->size << 9;
> >  			u64 offset = p.ptr.offset;
> >  
> >  			if (p.ptr.unwritten)
> >  				flags2 |= FIEMAP_EXTENT_UNWRITTEN;
> >  
> > -			if (p.crc.compression_type)
> > +			if (p.crc.compression_type) {
> >  				flags2 |= FIEMAP_EXTENT_ENCODED;
> > -			else
> > +				phys_len = p.crc.compressed_size << 9;
> > +			} else
> >  				offset += p.crc.offset;
> >  
> >  			if ((offset & (block_sectors(c) - 1)) ||
> > @@ -931,7 +933,7 @@ static int bch2_fill_extent(struct bch_fs *c,
> >  			ret = fiemap_fill_next_extent(info,
> >  						bkey_start_offset(k.k) << 9,
> >  						offset << 9,
> > -						k.k->size << 9, 0,
> > +						k.k->size << 9, phys_len,
> >  						flags|flags2);
> >  			if (ret)
> >  				return ret;
> > @@ -941,14 +943,18 @@ static int bch2_fill_extent(struct bch_fs *c,
> >  	} else if (bkey_extent_is_inline_data(k.k)) {
> >  		return fiemap_fill_next_extent(info,
> >  					       bkey_start_offset(k.k) << 9,
> > -					       0, k.k->size << 9, 0,
> > +					       0, k.k->size << 9,
> > +					       bkey_inline_data_bytes(k.k),
> 
> Question for Kent perhaps, but what's the functional difference between
> bkey_inline_data_bytes() and k->size in this particular case?

Not much - k->size will correspond to the size of the original write -
that is, the writeback write from the pagecache. inline_data_bytes is
the amount of data that wasn't zeroes.

So inline_data_bytes is probably the right thing to use here.