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6c3796d130
Generally target core and TCMUser seem to work fine for tape devices and media changers. But there is at least one situation where TCMUser is not able to support sequential access device emulation correctly. The situation is when an initiator sends a SCSI READ CDB with a length that is greater than the length of the tape block to read. We can distinguish two subcases: A) The initiator sent the READ CDB with the SILI bit being set. In this case the sequential access device has to transfer the data from the tape block (only the length of the tape block) and transmit a good status. The current interface between TCMUser and the userspace does not support reduction of the read data size by the userspace program. The patch below fixes this subcase by allowing the userspace program to specify a reduced data size in read direction. B) The initiator sent the READ CDB with the SILI bit not being set. In this case the sequential access device has to transfer the data from the tape block as in A), but additionally has to transmit CHECK CONDITION with the ILI bit set and NO SENSE in the sensebytes. The information field in the sensebytes must contain the residual count. With the below patch a user space program can specify the real read data length and appropriate sensebytes. TCMUser then uses the se_cmd flag SCF_TREAT_READ_AS_NORMAL, to force target core to transmit the real data size and the sensebytes. Note: the flag SCF_TREAT_READ_AS_NORMAL is introduced by Lee Duncan's patch "[PATCH v4] target: transport should handle st FM/EOM/ILI reads" from Tue, 15 May 2018 18:25:24 -0700. Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com> Acked-by: Mike Christie <mchristi@redhat.com> Reviewed-by: Lee Duncan <lduncan@suse.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> |
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