Re: [PATCH] udf: Fix free space reporting for metadata and virtual partitions

[Jan Kara <jack@suse.cz>]

On Wed 08-01-20 23:32:40, Pali Rohár wrote:
> On Wednesday 08 January 2020 13:19:19 Jan Kara wrote:
> > Free space on filesystems with metadata or virtual partition maps
> > currently gets misreported. This is because these partitions are just
> > remapped onto underlying real partitions from which keep track of free
> > blocks. Take this remapping into account when counting free blocks as
> > well.
> > 
> > Reported-by: Pali Rohár <pali.rohar@gmail.com>
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/udf/super.c | 19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)
> > 
> > I plan to take this patch to my tree.
> > 
> > diff --git a/fs/udf/super.c b/fs/udf/super.c
> > index 8c28e93e9b73..b89e420a4b85 100644
> > --- a/fs/udf/super.c
> > +++ b/fs/udf/super.c
> > @@ -2492,17 +2492,26 @@ static unsigned int udf_count_free_table(struct super_block *sb,
> >  static unsigned int udf_count_free(struct super_block *sb)
> >  {
> >  	unsigned int accum = 0;
> > -	struct udf_sb_info *sbi;
> > +	struct udf_sb_info *sbi = UDF_SB(sb);
> >  	struct udf_part_map *map;
> > +	unsigned int part = sbi->s_partition;
> > +	int ptype = sbi->s_partmaps[part].s_partition_type;
> > +
> > +	if (ptype == UDF_METADATA_MAP25) {
> > +		part = sbi->s_partmaps[part].s_type_specific.s_metadata.
> > +							s_phys_partition_ref;
> > +	} else if (ptype == UDF_VIRTUAL_MAP15 || ptype == UDF_VIRTUAL_MAP20) {
> > +		part = UDF_I(sbi->s_vat_inode)->i_location.
> > +							partitionReferenceNum;
> 
> Hello! I do not think that it make sense to report "free blocks" for
> discs with Virtual partition. By definition of VAT, all blocks prior to
> VAT are already "read-only" and therefore these blocks cannot be use for
> writing new data by any implementation. And because VAT is stored on the
> last block, in our model all blocks are "occupied".

Fair enough. Let's just always return 0 for disks with VAT partition.

> > +	}
> >  
> > -	sbi = UDF_SB(sb);
> >  	if (sbi->s_lvid_bh) {
> >  		struct logicalVolIntegrityDesc *lvid =
> >  			(struct logicalVolIntegrityDesc *)
> >  			sbi->s_lvid_bh->b_data;
> > -		if (le32_to_cpu(lvid->numOfPartitions) > sbi->s_partition) {
> > +		if (le32_to_cpu(lvid->numOfPartitions) > part) {
> >  			accum = le32_to_cpu(
> > -					lvid->freeSpaceTable[sbi->s_partition]);
> > +					lvid->freeSpaceTable[part]);
> 
> And in any case freeSpaceTable should not be used for discs with VAT.
> And we should ignore its value for discs with VAT.
> 
> UDF 2.60 2.2.6.2: Free Space Table values be maintained ... except ...
> for a virtual partition ...
> 
> And same applies for "partition with Access Type pseudo-overwritable".

Well this is handled by the 'accum == 0xffffffff' condition below. So we
effectively ignore these values.

> >  			if (accum == 0xFFFFFFFF)
> >  				accum = 0;
> >  		}

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR