floppy: support arbitrary first-sector numbers
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>
Cc: Alain Knaff <alain@linux.lu>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Karel Zak <kzak@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 9c0b494..cf64ddf 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -423,8 +423,15 @@
* 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 @@
}
}
}
- 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 @@
}
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 @@
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 @@
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 @@
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();
