erofs over fscache doesn't support the compressed layout yet. It will
cause NULL crash if there are compressed inodes contained when working
in fscache mode.

So far in the erofs based container image distribution scenarios
(RAFS v6), the compressed images are downloaded to local and then
decompressed as a erofs image of uncompressed layout. Then the erofs
image is mounted in fscache mode and serves as the container image. Thus
the current implementation won't break the container image distribution
scenarios.

The fscache support for the compressed layout is still under
development. Anyway, to avoid the potential crash, let's leave the
compressed inodes unsupported in fscache mode until we support it later.

Fixes: 1442b02b66ad ("erofs: implement fscache-based data read for non-inline layout")
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/inode.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index bcc8335b46b3..95a403720e8c 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -288,7 +288,10 @@ static int erofs_fill_inode(struct inode *inode, int isdir)
 	}
 
 	if (erofs_inode_is_data_compressed(vi->datalayout)) {
-		err = z_erofs_fill_inode(inode);
+		if (!erofs_is_fscache_mode(inode->i_sb))
+			err = z_erofs_fill_inode(inode);
+		else
+			err = -EOPNOTSUPP;
 		goto out_unlock;
 	}
 	inode->i_mapping->a_ops = &erofs_raw_access_aops;
-- 
2.27.0

Hi Jeffle,

On Wed, May 25, 2022 at 03:59:50PM +0800, Jeffle Xu wrote:
> erofs over fscache doesn't support the compressed layout yet. It will
> cause NULL crash if there are compressed inodes contained when working
> in fscache mode.
> 
> So far in the erofs based container image distribution scenarios
> (RAFS v6), the compressed images are downloaded to local and then

... the compressed RAFS v6 images are downloaded and then decompressed
on demand as an uncompressed erofs image.

> decompressed as a erofs image of uncompressed layout. Then the erofs
> image is mounted in fscache mode and serves as the container image. Thus

... in fscache mode for containers to use. IOWs

> the current implementation won't break the container image distribution
> scenarios.

IOWs, currently compressed data is decompressed on the userspace side
instead and uncompressed erofs images will be finally cached.

> 
> The fscache support for the compressed layout is still under
> development. Anyway, to avoid the potential crash, let's leave the

The fscache support for the compressed layout is still under
development and it will be used for runtime decompression feature.
Anyway..

> compressed inodes unsupported in fscache mode until we support it later.
> 
> Fixes: 1442b02b66ad ("erofs: implement fscache-based data read for non-inline layout")

Otherwise looks good to me,

Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang