Re: [PATCH] floppy: support arbitrary first-sector numbers

[Randy Dunlap <randy.dunlap@oracle.com>]

On Thu, 21 Aug 2008 12:39:49 -0700 Andrew Morton wrote:

> On Sat, 9 Aug 2008 19:42:14 +0100
> Keith Wansbrough <keith@lochan.org> wrote:
> 
> > The current floppy_struct allows floppies to number sectors starting
> > from 0 or 1.  This patch allows arbitrary first-sector numbers - for
> > example, 0xC1 for Amstrad CPC disks.
> > 
> > This extends the existing 1-bit field (FD_ZEROBASED, bit 2 of stretch) 
> > to 8 bits (FD_SECTMASK, bits 2 to 9).
> > 
> > Currently 0x00 denotes a first sector number of 1, and 0x01 denotes a
> > first sector number of 0.  We extend this by interpreting FD_SECTMASK
> > as the first sector number with the LSB flipped.
> > 
> > Signed-off-by: Keith Wansbrough <keith@lochan.org>
> > ---
> > 
> > I've tested formatting, writing, and reading disks with a variety of
> > first sector numbers (including 0 and 1), and all works as expected.
> > 
> > I have made corresponding changes to fdutils, which I will submit
> > separately to the fdutils maintainer.
> > 
> > There's no floppy maintainer listed in MAINTAINERS, so this is sent to
> > the block subsystem maintainer and to the fdutils maintainer.  I'm cc:ing
> > Gene because I know he's been working in this area recently.
> > 
> > --KW 8-)
> > 
> > Index: linux-2.6.27-rc1-git4/drivers/block/floppy.c
> > ===================================================================
> > --- linux-2.6.27-rc1-git4.orig/drivers/block/floppy.c	2008-08-02 23:36:32.000000000 +0100
> > +++ linux-2.6.27-rc1-git4/drivers/block/floppy.c	2008-08-02 23:36:37.000000000 +0100
> > @@ -423,8 +423,15 @@ static struct floppy_raw_cmd *raw_cmd, d
> >   * 1581's logical side 0 is on physical side 1, whereas the Sharp's logical
> >   * side 0 is on physical side 0 (but with the misnamed sector IDs).
> >   * 'stretch' should probably be renamed to something more general, like
> > - * 'options'.  Other parameters should be self-explanatory (see also
> > - * setfdprm(8)).
> > + * 'options'.
> > + *
> > + * Bits 2 through 9 of 'stretch' tell the number of the first sector.
> > + * The LSB (bit 2) is flipped. For most disks, the first sector
> > + * is 1 (represented by 0x00<<2).  For some CP/M and music sampler
> > + * disks (such as Ensoniq EPS 16plus) it is 0 (represented as 0x01<<2).
> > + * For Amstrad CPC disks it is 0xC1 (represented as 0xC0<<2).
> > + *
> > + * Other parameters should be self-explanatory (see also setfdprm(8)).
> >   */
> >  /*
> >  	    Size
> > @@ -2236,9 +2243,9 @@ static void setup_format_params(int trac
> >  			}
> >  		}
> >  	}
> > -	if (_floppy->stretch & FD_ZEROBASED) {
> > +	if (_floppy->stretch & FD_SECTBASEMASK) {
> >  		for (count = 0; count < F_SECT_PER_TRACK; count++)
> > -			here[count].sect--;
> > +			here[count].sect += FD_SECTBASE(_floppy) - 1;
> >  	}
> >  }
> >  
> > @@ -2649,7 +2656,7 @@ static int make_raw_rw_request(void)
> >  	}
> >  	HEAD = fsector_t / _floppy->sect;
> >  
> > -	if (((_floppy->stretch & (FD_SWAPSIDES | FD_ZEROBASED)) ||
> > +	if (((_floppy->stretch & (FD_SWAPSIDES | FD_SECTBASEMASK)) ||
> >  	     TESTF(FD_NEED_TWADDLE)) && fsector_t < _floppy->sect)
> >  		max_sector = _floppy->sect;
> >  
> > @@ -2679,7 +2686,7 @@ static int make_raw_rw_request(void)
> >  	CODE2SIZE;
> >  	SECT_PER_TRACK = _floppy->sect << 2 >> SIZECODE;
> >  	SECTOR = ((fsector_t % _floppy->sect) << 2 >> SIZECODE) +
> > -	    ((_floppy->stretch & FD_ZEROBASED) ? 0 : 1);
> > +	    FD_SECTBASE(_floppy);
> >  
> >  	/* tracksize describes the size which can be filled up with sectors
> >  	 * of size ssize.
> > @@ -3311,7 +3318,7 @@ static inline int set_geometry(unsigned 
> >  	    g->head <= 0 ||
> >  	    g->track <= 0 || g->track > UDP->tracks >> STRETCH(g) ||
> >  	    /* check if reserved bits are set */
> > -	    (g->stretch & ~(FD_STRETCH | FD_SWAPSIDES | FD_ZEROBASED)) != 0)
> > +	    (g->stretch & ~(FD_STRETCH | FD_SWAPSIDES | FD_SECTBASEMASK)) != 0)
> >  		return -EINVAL;
> >  	if (type) {
> >  		if (!capable(CAP_SYS_ADMIN))
> > @@ -3356,7 +3363,7 @@ static inline int set_geometry(unsigned 
> >  		if (DRS->maxblock > user_params[drive].sect ||
> >  		    DRS->maxtrack ||
> >  		    ((user_params[drive].sect ^ oldStretch) &
> > -		     (FD_SWAPSIDES | FD_ZEROBASED)))
> > +		     (FD_SWAPSIDES | FD_SECTBASEMASK)))
> >  			invalidate_drive(bdev);
> >  		else
> >  			process_fd_request();
> > Index: linux-2.6.27-rc1-git4/include/linux/fd.h
> > ===================================================================
> > --- linux-2.6.27-rc1-git4.orig/include/linux/fd.h	2008-08-02 23:36:32.000000000 +0100
> > +++ linux-2.6.27-rc1-git4/include/linux/fd.h	2008-08-02 23:36:37.000000000 +0100
> > @@ -15,10 +15,16 @@ struct floppy_struct {
> >  			sect,		/* sectors per track */
> >  			head,		/* nr of heads */
> >  			track,		/* nr of tracks */
> > -			stretch;	/* !=0 means double track steps */
> > +			stretch;	/* bit 0 !=0 means double track steps */
> > +					/* bit 1 != 0 means swap sides */
> > +					/* bits 2..9 give the first sector */
> > +					/*  number (the LSB is flipped) */
> >  #define FD_STRETCH 1
> >  #define FD_SWAPSIDES 2
> >  #define FD_ZEROBASED 4
> > +#define FD_SECTBASEMASK 0x3FC
> > +#define FD_MKSECTBASE(s) (((s) ^ 1) << 2)
> > +#define FD_SECTBASE(floppy) ((((floppy)->stretch & FD_SECTBASEMASK) >> 2) ^ 1)
> >  
> >  	unsigned char	gap,		/* gap1 size */
> >  
> 
> So this is a backward-compatible enhancement to the floppy FDSETPRM and
> FDDEFPRM ioctl.  If some userspace wasn't setting those bits to zero,
> it loses, and probably deserved to.
> 
> I'd suggest an update to the FDDEFPRM documentation, only it isn't
> documented.
> 
> Who is the fdutils maintainer?

man fdformat says:

AVAILABILITY
       The  fdformat command is part of the util-linux-ng package and is avail-
       able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

so the maintainer is   Karel Zak <kzak@redhat.com>

---
~Randy
Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA
http://linuxplumbersconf.org/