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SubjectRe: [PATCH] floppy: support arbitrary first-sector numbers
On Thu, Aug 21, 2008 at 12:51:01PM -0700, Randy Dunlap wrote:
> 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>

Andrew - thanks for adding.

Randy - I've cc'd the fdutils maintainer (alain@linux.lu,
http://fdutils.linux.lu) on this patch. fdutils recommends not using
fdformat(8) but using superformat(1) instead, and uses setfdprm(1) to
set floppy parameters.

I've sent an fdutils patch to Alain, but haven't heard back yet. I
couldn't find any appropriate docs to update.

Cheers,

--KW 8-)


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