RE: [PATCH v5 3/7] fsdax: Add dax_iomap_cow_copy() for dax_iomap_zero

["ruansy.fnst@fujitsu.com" <ruansy.fnst@fujitsu.com>]

> -----Original Message-----
> From: Darrick J. Wong <djwong@kernel.org>
> Subject: Re: [PATCH v5 3/7] fsdax: Add dax_iomap_cow_copy() for
> dax_iomap_zero
> 
> On Tue, May 11, 2021 at 11:09:29AM +0800, Shiyang Ruan wrote:
> > Punch hole on a reflinked file needs dax_copy_edge() too.  Otherwise,
> > data in not aligned area will be not correct.  So, add the srcmap to
> > dax_iomap_zero() and replace memset() as dax_copy_edge().
> >
> > Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> > Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
> > ---
> >  fs/dax.c               | 25 +++++++++++++++----------
> >  fs/iomap/buffered-io.c |  2 +-
> >  include/linux/dax.h    |  3 ++-
> >  3 files changed, 18 insertions(+), 12 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index ef0e564e7904..ee9d28a79bfb 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1186,7 +1186,8 @@ static vm_fault_t dax_pmd_load_hole(struct
> > xa_state *xas, struct vm_fault *vmf,  }  #endif /* CONFIG_FS_DAX_PMD
> > */
> >
> > -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
> > +s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> > +		struct iomap *srcmap)
> >  {
> >  	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
> >  	pgoff_t pgoff;
> > @@ -1208,19 +1209,23 @@ s64 dax_iomap_zero(loff_t pos, u64 length,
> > struct iomap *iomap)
> >
> >  	if (page_aligned)
> >  		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
> > -	else
> > +	else {
> >  		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
> > -	if (rc < 0) {
> > -		dax_read_unlock(id);
> > -		return rc;
> > -	}
> > -
> > -	if (!page_aligned) {
> > -		memset(kaddr + offset, 0, size);
> > +		if (rc < 0)
> > +			goto out;
> > +		if (iomap->addr != srcmap->addr) {
> 
> Why isn't this "if (srcmap->type != IOMAP_HOLE)" ?
> 
> I suppose it has the same effect, since @iomap should never be a hole and we
> should never have a @srcmap that's the same as @iomap, but still, we use
> IOMAP_HOLE checks in most other parts of fs/iomap/.

According to its caller `iomap_zero_range_actor()`, whether srcmap->type is IOMAP_HOLE has already been checked before `dax_iomap_zero()`.  So the check you suggested will always be true...


--
Thanks,
Ruan Shiyang.

> 
> Other than that, the logic looks decent to me.
> 
> --D
> 
> > +			rc = dax_iomap_cow_copy(offset, size, PAGE_SIZE, srcmap,
> > +						kaddr);
> > +			if (rc < 0)
> > +				goto out;
> > +		} else
> > +			memset(kaddr + offset, 0, size);
> >  		dax_flush(iomap->dax_dev, kaddr + offset, size);
> >  	}
> > +
> > +out:
> >  	dax_read_unlock(id);
> > -	return size;
> > +	return rc < 0 ? rc : size;
> >  }
> >
> >  static loff_t
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index
> > f2cd2034a87b..2734955ea67f 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -933,7 +933,7 @@ static loff_t iomap_zero_range_actor(struct inode
> *inode, loff_t pos,
> >  		s64 bytes;
> >
> >  		if (IS_DAX(inode))
> > -			bytes = dax_iomap_zero(pos, length, iomap);
> > +			bytes = dax_iomap_zero(pos, length, iomap, srcmap);
> >  		else
> >  			bytes = iomap_zero(inode, pos, length, iomap, srcmap);
> >  		if (bytes < 0)
> > diff --git a/include/linux/dax.h b/include/linux/dax.h index
> > b52f084aa643..3275e01ed33d 100644
> > --- a/include/linux/dax.h
> > +++ b/include/linux/dax.h
> > @@ -237,7 +237,8 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault
> > *vmf,  int dax_delete_mapping_entry(struct address_space *mapping,
> > pgoff_t index);  int dax_invalidate_mapping_entry_sync(struct
> address_space *mapping,
> >  				      pgoff_t index);
> > -s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap);
> > +s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap,
> > +		struct iomap *srcmap);
> >  static inline bool dax_mapping(struct address_space *mapping)  {
> >  	return mapping->host && IS_DAX(mapping->host);
> > --
> > 2.31.1
> >
> >
> >
>