Re: [PATCH] erofs: encode file handle with the internal helpers

[Gao Xiang <xiang@kernel.org>]

Hi Hongbo,

I think the subject can be updated as:
`erofs-utils: fix file handle encoding for 64-bit NIDs`

On Tue, Apr 29, 2025 at 01:11:39AM +0000, Hongbo Li wrote:
> In erofs, the inode number has the location information of
> files. The default encode_fh uses the ino32, this will lack
> of some information when the file is too big. So we need
> the internal helpers to encode filehandle.
> 
> Since i_generation in EROFS is not used, here we only encode
> the nid into file handle when it is exported. So it is easy
> to parse the dentry from file handle.

If `FILEID_INO64_GEN_PARENT` is used, I don't think
the generation number should be emitted, as documented as:

`
/*
 * 64 bit inode number, 32 bit generation number.
 */
FILEID_INO64_GEN = 0x81,

/*
 * 64 bit inode number, 32 bit generation number,
 * 64 bit parent inode number, 32 bit parent generation.
 */
FILEID_INO64_GEN_PARENT = 0x82,
` 

Even the generation number is 0 but we might use
i_generation for some remote update use cases
in the future.

> 
> It is easy to reproduce test:
>   1. prepare an erofs image with nid bigger than UINT_MAX
>   2. mount -t erofs foo.img /mnt/erofs
>   3. set exportfs with configuration: /mnt/erofs *(rw,sync,
>      no_root_squash)
>   4. mount -t nfs $IP:/mnt/erofs /mnt/nfs
>   5. md5sum /mnt/nfs/foo # foo is the file which nid bigger
>      than UINT_MAX.
> For overlayfs case, the under filesystem's file handle is
> encoded in ovl_fb.fid, it is same as NFS's case.

Can we have a way to add a testcase for the overlayfs case:
since it's somewhat complex to write a testcase with nfs
above.

> 
> Fixes: 3e917cc305c6 ("erofs: make filesystem exportable")
> Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
> ---
>  fs/erofs/super.c | 51 ++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 43 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index cadec6b1b554..8f787c47e04d 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -511,24 +511,59 @@ static int erofs_fc_parse_param(struct fs_context *fc,
>  	return 0;
>  }
>  
> -static struct inode *erofs_nfs_get_inode(struct super_block *sb,
> -					 u64 ino, u32 generation)
> +static int erofs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
> +			   struct inode *parent)
>  {
> -	return erofs_iget(sb, ino);
> +	int len = parent ? 4 : 2;
> +	erofs_nid_t nid;
> +
> +	if (*max_len < len) {
> +		*max_len = len;
> +		return FILEID_INVALID;
> +	}
> +
> +	nid = EROFS_I(inode)->nid;
> +	fh[0] = (u32)(nid >> 32);
> +	fh[1] = (u32)(nid & 0xffffffff);
> +
> +	if (parent) {
> +		nid = EROFS_I(parent)->nid;
> +
> +		fh[2] = (u32)(nid >> 32);
> +		fh[3] = (u32)(nid & 0xffffffff);
> +	}
> +
> +	*max_len = len;
> +	return parent ? FILEID_INO64_GEN_PARENT : FILEID_INO64_GEN;
>  }
>  
>  static struct dentry *erofs_fh_to_dentry(struct super_block *sb,
>  		struct fid *fid, int fh_len, int fh_type)
>  {
> -	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
> -				    erofs_nfs_get_inode);
> +	erofs_nid_t nid;
> +
> +	if ((fh_type != FILEID_INO64_GEN &&
> +	     fh_type != FILEID_INO64_GEN_PARENT) || fh_len < 2)
> +		return NULL;
> +
> +	nid = (u64) fid->raw[0] << 32;
> +	nid |= (u64) fid->raw[1];
> +

Redundant new line.

> +	return d_obtain_alias(erofs_iget(sb, nid));
>  }
>  
>  static struct dentry *erofs_fh_to_parent(struct super_block *sb,
>  		struct fid *fid, int fh_len, int fh_type)
>  {
> -	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
> -				    erofs_nfs_get_inode);
> +	erofs_nid_t nid;
> +
> +	if (fh_type != FILEID_INO64_GEN_PARENT || fh_len < 4)
> +		return NULL;
> +
> +	nid = (u64) fid->raw[2] << 32;
> +	nid |= (u64) fid->raw[3];
> +

Same here.

Thanks,
Gao Xiang