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s390/tape: Add support for bigger block sizes

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The tape device type 3590/3592 and emulated 3490 VTS can handle a block
size of up to 256K bytes. Currently the tape device driver is limited to
a block size of 65535 bytes (64K-1). This limitation stems from the
maximum of 65535 bytes of data that can be transferred with one
Channel-Command Word (CCW).

To work around this limitation data chaining is used which uses several
CCW to transfer an entire 256K block of data. A single CCW holds a
maximum of 65535 bytes of data.

Set MAX_BLOCKSIZE to 262144 (= 256K) to allow for data transfers with
larger block sizes. The read_block() and write_block() discipline
functions calculate the number of CCWs required based on the IDAL buffer
array size that was created for a given block size. If there is more
than one CCW required for the data transfer, the new helper function
tape_ccw_dc_idal() is used to build the data chain accordingly.

The Interruption-Repsonse Block (irb) is added to the tape_request
struct so that the tapechar_read/write() functions can analyze what data
was read or written accordingly.

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Jan Höppner 2025-10-16 09:47:18 +02:00 • committed by Heiko Carstens
commit 319d3d6653
5 changed files with 86 additions and 34 deletions
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