Re: [PATCH] btrfs: reflink: Assure length != 0 in btrfs_extent_same()

[Sidong Yang <realwakka@gmail.com>]

On Thu, Aug 19, 2021 at 11:04:58AM +0300, Nikolay Borisov wrote:
> 
> 
> On 18.08.21 г. 19:08, Sidong Yang wrote:
> > btrfs_extent_same() cannot be called with zero length. Because when
> > length is zero, it would be filtered by condition in
> > btrfs_remap_file_range(). But if this function is used in other case in
> > future, it can make ret as uninitialized.
> > 
> > Signed-off-by: Sidong Yang <realwakka@gmail.com>
> 
> This is not sufficient, with the assert compiled out the error would
> still be in place. It seem that it is sufficient to initialize ret to
> some non-arbitrary value i.e -EINVAL ?

I agree. It's better way to assign intial value than adding assert. If
there is code that initialize ret, It seems that assert is no need for
this.
> 
> > ---
> >  fs/btrfs/reflink.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/fs/btrfs/reflink.c b/fs/btrfs/reflink.c
> > index 9b0814318e72..69eb50f2f0b4 100644
> > --- a/fs/btrfs/reflink.c
> > +++ b/fs/btrfs/reflink.c
> > @@ -653,6 +653,7 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
> >  	u64 i, tail_len, chunk_count;
> >  	struct btrfs_root *root_dst = BTRFS_I(dst)->root;
> >  
> > +	ASSERT(olen);
> >  	spin_lock(&root_dst->root_item_lock);
> >  	if (root_dst->send_in_progress) {
> >  		btrfs_warn_rl(root_dst->fs_info,
> >