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scsi: target: transport should handle st FM/EOM/ILI reads 

When a tape drive is exported via LIO using the pscsi module, a read
that requests more bytes per block than the tape can supply returns an
empty buffer. This is because the pscsi pass-through target module sees
the "ILI" illegal length bit set and thinks there is no reason to return
the data.

This is a long-standing transport issue, since it assumes that no data
need be returned under a check condition, which isn't always the case
for tape.

Add in a check for tape reads with the ILI, EOM, or FM bits set, with a
sense code of NO_SENSE, treating such cases as if the read
succeeded. The layered tape driver then "does the right thing" when it
gets such a response.

Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Lee Duncan 2018-05-15 18:25:24 -07:00 committed by Martin K. Petersen
parent 51b910c3c7
commit bd81372065
3 changed files with 62 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
drivers/target/target_core_pscsi.c
View File

@ -689,8 +689,29 @@ after_mode_sense:
}
after_mode_select:
if (scsi_status == SAM_STAT_CHECK_CONDITION)
if (scsi_status == SAM_STAT_CHECK_CONDITION) {
transport_copy_sense_to_cmd(cmd, req_sense);
/*
* check for TAPE device reads with
* FM/EOM/ILI set, so that we can get data
* back despite framework assumption that a
* check condition means there is no data
*/
if (sd->type == TYPE_TAPE &&
cmd->data_direction == DMA_FROM_DEVICE) {
/*
* is sense data valid, fixed format,
* and have FM, EOM, or ILI set?
*/
if (req_sense[0] == 0xf0 && /* valid, fixed format */
req_sense[2] & 0xe0 && /* FM, EOM, or ILI */
(req_sense[2] & 0xf) == 0) { /* key==NO_SENSE */
pr_debug("Tape FM/EOM/ILI status detected. Treat as normal read.\n");
cmd->se_cmd_flags |= SCF_TREAT_READ_AS_NORMAL;
}
}
}
}
enum {
@ -1061,7 +1082,8 @@ static void pscsi_req_done(struct request *req, blk_status_t status)
switch (host_byte(result)) {
case DID_OK:
target_complete_cmd(cmd, scsi_status);
target_complete_cmd_with_length(cmd, scsi_status,
cmd->data_length - scsi_req(req)->resid_len);
break;
default:
pr_debug("PSCSI Host Byte exception at cmd: %p CDB:"

43
drivers/target/target_core_transport.c
View File

@ -779,7 +779,9 @@ EXPORT_SYMBOL(target_complete_cmd);
void target_complete_cmd_with_length(struct se_cmd *cmd, u8 scsi_status, int length)
{
if (scsi_status == SAM_STAT_GOOD && length < cmd->data_length) {
if ((scsi_status == SAM_STAT_GOOD ||
cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL) &&
length < cmd->data_length) {
if (cmd->se_cmd_flags & SCF_UNDERFLOW_BIT) {
cmd->residual_count += cmd->data_length - length;
} else {
@ -2084,12 +2086,24 @@ static void transport_complete_qf(struct se_cmd *cmd)
goto queue_status;
}
if (cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE)
/*
* Check if we need to send a sense buffer from
* the struct se_cmd in question. We do NOT want
* to take this path of the IO has been marked as
* needing to be treated like a "normal read". This
* is the case if it's a tape read, and either the
* FM, EOM, or ILI bits are set, but there is no
* sense data.
*/
if (!(cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL) &&
cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE)
goto queue_status;
switch (cmd->data_direction) {
case DMA_FROM_DEVICE:
if (cmd->scsi_status)
/* queue status if not treating this as a normal read */
if (cmd->scsi_status &&
!(cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL))
goto queue_status;
trace_target_cmd_complete(cmd);
@ -2194,9 +2208,15 @@ static void target_complete_ok_work(struct work_struct *work)
/*
* Check if we need to send a sense buffer from
* the struct se_cmd in question.
* the struct se_cmd in question. We do NOT want
* to take this path of the IO has been marked as
* needing to be treated like a "normal read". This
* is the case if it's a tape read, and either the
* FM, EOM, or ILI bits are set, but there is no
* sense data.
*/
if (cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE) {
if (!(cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL) &&
cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE) {
WARN_ON(!cmd->scsi_status);
ret = transport_send_check_condition_and_sense(
cmd, 0, 1);
@ -2238,7 +2258,18 @@ static void target_complete_ok_work(struct work_struct *work)
queue_rsp:
switch (cmd->data_direction) {
case DMA_FROM_DEVICE:
if (cmd->scsi_status)
/*
* if this is a READ-type IO, but SCSI status
* is set, then skip returning data and just
* return the status -- unless this IO is marked
* as needing to be treated as a normal read,
* in which case we want to go ahead and return
* the data. This happens, for example, for tape
* reads with the FM, EOM, or ILI bits set, with
* no sense data.
*/
if (cmd->scsi_status &&
!(cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL))
goto queue_status;
atomic_long_add(cmd->data_length,

1
include/target/target_core_base.h
View File

@ -143,6 +143,7 @@ enum se_cmd_flags_table {
SCF_ACK_KREF = 0x00400000,
SCF_USE_CPUID = 0x00800000,
SCF_TASK_ATTR_SET = 0x01000000,
SCF_TREAT_READ_AS_NORMAL = 0x02000000,
};
/*