Re: [PATCH] xfs_db: take BB cluster offset into account when using 'type' cmd

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Apr 19, 2022 at 06:56:00PM +0200, Andrey Albershteyn wrote:
> On Tue, Apr 19, 2022 at 08:47:50AM -0700, Darrick J. Wong wrote:
> > On Tue, Apr 19, 2022 at 02:19:51PM +0200, Andrey Albershteyn wrote:
> > > Changing the interpretation type of data under the cursor moves the
> > > cursor to the beginning of BB cluster. When cursor is set to an
> > > inode the cursor is offset in BB buffer. However, this offset is not
> > > considered when type of the data is changed - the cursor points to
> > > the beginning of BB buffer. For example:
> > > 
> > > $ xfs_db -c "inode 131" -c "daddr" -c "type text" \
> > > 	-c "daddr" /dev/sdb1
> > > current daddr is 131
> > > current daddr is 128
> > > 
> > > Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
> > > ---
> > >  db/io.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/db/io.c b/db/io.c
> > > index df97ed91..107f2e11 100644
> > > --- a/db/io.c
> > > +++ b/db/io.c
> > > @@ -589,6 +589,7 @@ set_iocur_type(
> > >  	const typ_t	*type)
> > >  {
> > >  	int		bb_count = 1;	/* type's size in basic blocks */
> > > +	int boff = iocur_top->boff;
> > 
> > Nit: Please line up the variable names.
> 
> sure ;)
> 
> > 
> > >  
> > >  	/*
> > >  	 * Inodes are special; verifier checks all inodes in the chunk, the
> > > @@ -613,6 +614,9 @@ set_iocur_type(
> > >  		bb_count = BTOBB(byteize(fsize(type->fields,
> > >  				       iocur_top->data, 0, 0)));
> > >  	set_cur(type, iocur_top->bb, bb_count, DB_RING_IGN, NULL);
> > > +	iocur_top->boff = boff;
> > > +	iocur_top->off = ((xfs_off_t)iocur_top->bb << BBSHIFT) + boff;
> > > +	iocur_top->data = (void *)((char *)iocur_top->buf + boff);
> > 
> > It seems reasonable to me to preserve the io cursor's boff when we're
> > setting /only/ the buffer type, but this function and off_cur() could
> > share these three lines of code that (re)set boff/off/data.
> > 
> > Alternately, I guess you could just call off_cur(boff, BBTOB(bb_count))
> > here.
> 
> This won't pass the second condition in off_cur(). I suppose the
> purpose of off_cur() was to shift io cursor in BB buffer. But
> changing the type changes the blen which could be smaller (e.g.
> inode blen == 32 -> text blen == 1). Anyway, will try to come up
> with a meaningful name for this 3 lines function :)

Ooh, a bikeshed!  How about:

static inline void set_cur_boff(int boff)
{
	iocur_top->boff = boff;
	iocur_top->off = ((xfs_off_t)iocur_top->bb << BBSHIFT) + boff;
	iocur_top->data = (void *)((char *)iocur_top->buf + boff);
}

> I think the other solution could be to set boff in set_cur(), but
> this will require more refactoring and I suppose this is the only
> place where newly added argument would be used.
> 
> > 
> > --D
> > 
> > >  }
> > >  
> > >  static void
> > > -- 
> > > 2.27.0
> > > 
> > 
> 
> -- 
> - Andrey
>