Re: [PATCH v2 4/9] exfat: add support for multi-cluster allocation

[Chi Zhiling]

On 5/11/26 08:20, Namjae Jeon wrote:
> > > diff --git a/fs/exfat/inode.c b/fs/exfat/inode.c
> > > index 1246713567a5..7b09d94ac464 100644
> > > --- a/fs/exfat/inode.c
> > > +++ b/fs/exfat/inode.c
> > > @@ -137,9 +137,9 @@ static int exfat_map_cluster(struct inode *inode, unsigned int clu_offset,
> > >        unsigned int num_to_be_allocated = 0, num_clusters;
> > >
> > >        num_clusters = exfat_bytes_to_cluster(sbi, exfat_ondisk_size(inode));
> > > -
> > > -     if (clu_offset >= num_clusters)
> > > -             num_to_be_allocated = clu_offset - num_clusters + 1;
> > > +     if (clu_offset > num_clusters ||
> > > +         *count > num_clusters - clu_offset)
> > > +             num_to_be_allocated = clu_offset + *count - num_clusters;
> >
> > We need to truncate *count for read operations so that it does not
> > extend beyond EOF. Otherwise, xfstests generic/003 will fail.
> I'm not seeing this failure... Can you elaborate more why it was
> failing on your side ?

In my vm with 6G ram and 40G test disk, when the cluster size is 512 
bytes, reading a 512-byte file (which consists of one cluster) fails 
because iomap attempts to fetch a map for the 0–4K range, which exceeds 
the file's EOF.