s390/dasd: Add range-based format-track collision detection

Replace the single per-device format_entry slot with an array of 16
slots so multiple format requests can be in flight at once, and extend
struct dasd_format_entry with a start_trk/end_trk/cqr range (replacing
the single track field).

Rewrite test_and_set_format_track() to scan the array for range overlaps
instead of a trkcount snapshot, honour the early-collision flag, and
return the allocated slot to the caller.

Add dasd_req_conflict() and extend dasd_return_cqr_cb() to mark in-flight
data CQRs that overlap a just-completed format range, so the next
test_and_set_format_track() detects the conflict early.

Remove the now-obsolete trkcount snapshot in dasd_start_IO().

The detection added here only becomes active together with the
WRITE_FULL_TRACK ESE format handler later in the series: that patch routes
the format request through dasd_return_cqr_cb() (so completion runs the
overlap hook with cqr->format set) and records each request's
start_trk/end_trk range. Until then the array and the conflict check are in
place but dormant.

Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-10-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions