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Date: Thu, 21 Aug 2008 12:51:01 -0700
From: Randy Dunlap <randy.dunlap@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Keith Wansbrough <keith@...han.org>, axboe@...nel.dk,
alain@...ux.lu, linux-kernel@...r.kernel.org,
gene.heskett@...il.com,
Michael Kerrisk <mtk.manpages@...glemail.com>
Subject: Re: [PATCH] floppy: support arbitrary first-sector numbers
On Thu, 21 Aug 2008 12:39:49 -0700 Andrew Morton wrote:
> On Sat, 9 Aug 2008 19:42:14 +0100
> Keith Wansbrough <keith@...han.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@...han.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@...hat.com>
---
~Randy
Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA
http://linuxplumbersconf.org/
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