On Thu 29-08-19 21:45:17, Matthew Bobrowski wrote:
> > > @@ -3581,10 +3611,10 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> > > iomap->type = delalloc ? IOMAP_DELALLOC : IOMAP_HOLE;
> > > iomap->addr = IOMAP_NULL_ADDR;
> > > } else {
> > > - if (map.m_flags & EXT4_MAP_MAPPED) {
> > > - iomap->type = IOMAP_MAPPED;
> > > - } else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> > > + if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> > > iomap->type = IOMAP_UNWRITTEN;
> > > + } else if (map.m_flags & EXT4_MAP_MAPPED) {
> > > + iomap->type = IOMAP_MAPPED;
> > > } else {
> > > WARN_ON_ONCE(1);
> > > return -EIO;
> >
> > Possibly this hunk should go into a separate patch (since this is not
> > directly related with iomap conversion) with a changelog / comment
> > explaining why we need to check EXT4_MAP_UNWRITTEN first.
>
> But wouldn't doing so break bisection? Seeing as though we needed to
> change this statement specifically to accommodate for the weirdness
> being returned from ext4_map_blocks()? i.e. map.m_flags being set to
> either of the following:
>
> - (EXT4_MAP_NEW | EXT4_MAP_MAPPED)
> or
> - (EXT4_MAP_NEW | EXT4_MAP_MAPPED | EXT4_MAP_UNWRITTEN)
>
> So, if we left the statement in its original form, we'd allocate
> unwritten extents but never actually get around to converting them in
> ext4_dio_write_end_io() as IOMAP_DIO_UNWRITTEN would never be set?
By splitting into a separate patch, I meant that patch would go before this
one. Original code in ext4_iomap_begin() never called ext4_map_blocks()
with a set of flags that can return with both EXT4_MAP_MAPPED and
EXT4_MAP_UNWRITTEN set so that patch would be a no-op but would fix that
landmine you tripped over.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
