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>
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Jens Axboe

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061837bc86
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9e49184c82
@@ -15,10 +15,16 @@ struct floppy_struct {
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sect, /* sectors per track */
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head, /* nr of heads */
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track, /* nr of tracks */
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stretch; /* !=0 means double track steps */
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stretch; /* bit 0 !=0 means double track steps */
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/* bit 1 != 0 means swap sides */
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/* bits 2..9 give the first sector */
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/* number (the LSB is flipped) */
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#define FD_STRETCH 1
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#define FD_SWAPSIDES 2
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#define FD_ZEROBASED 4
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#define FD_SECTBASEMASK 0x3FC
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#define FD_MKSECTBASE(s) (((s) ^ 1) << 2)
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#define FD_SECTBASE(floppy) ((((floppy)->stretch & FD_SECTBASEMASK) >> 2) ^ 1)
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unsigned char gap, /* gap1 size */
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