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scsi: target: tcmu: add read length support

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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>
This commit is contained in:
bstroesser@ts.fujitsu.com
2018-05-24 18:49:41 +02:00
committed by Martin K. Petersen
parent ce397d215c
commit 6c3796d130
2 changed files with 39 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
include/uapi/linux/target_core_user.h
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@@ -44,6 +44,7 @@
#define TCMU_MAILBOX_VERSION 2
#define ALIGN_SIZE 64 /* Should be enough for most CPUs */
#define TCMU_MAILBOX_FLAG_CAP_OOOC (1 << 0) /* Out-of-order completions */
#define TCMU_MAILBOX_FLAG_CAP_READ_LEN (1 << 1) /* Read data length */
struct tcmu_mailbox {
__u16 version;
@@ -71,6 +72,7 @@ struct tcmu_cmd_entry_hdr {
__u16 cmd_id;
__u8 kflags;
#define TCMU_UFLAG_UNKNOWN_OP 0x1
#define TCMU_UFLAG_READ_LEN 0x2
__u8 uflags;
} __packed;
@@ -119,7 +121,7 @@ struct tcmu_cmd_entry {
__u8 scsi_status;
__u8 __pad1;
__u16 __pad2;
__u32 __pad3;
__u32 read_len;
char sense_buffer[TCMU_SENSE_BUFFERSIZE];
} rsp;
};