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
assume 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 the ILI, EOM,
or FM bits set, with a sense code of NO_SENSE,
treating such cases as if there is no sense data
and the read succeeded. The layered tape driver then
"does the right thing" when it gets such a response.
Changes from RFC:
- Moved ugly code from transport to pscsi module
- Added checking EOM and FM bits, as well as ILI
- fixed malformed patch
- Clarified description a bit
Signed-off-by: Lee Duncan <lduncan@xxxxxxxx>
---
drivers/target/target_core_pscsi.c | 22 +++++++++++++++++++++-
drivers/target/target_core_transport.c | 6 ++++++
include/target/target_core_base.h | 1 +
3 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 0d99b242e82e..b237104af81c 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -689,8 +689,28 @@ static void pscsi_complete_cmd(struct se_cmd *cmd, u8 scsi_status,
}
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);
+
+ /*
+ * hack to 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 */
+ cmd->se_cmd_flags |= SCF_TREAT_READ_AS_NORMAL;
+ }
+ }
+ }
}
enum {
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 74b646f165d4..56661a824266 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2192,6 +2192,11 @@ static void target_complete_ok_work(struct work_struct *work)
if (atomic_read(&cmd->se_dev->dev_qf_count) != 0)
schedule_work(&cmd->se_dev->qf_work_queue);
+ if (cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL) {
+ pr_debug("Tape FM/EOM/ILI status detected. Treating as OK\n");
+ goto treat_as_normal_read;
+ }
+
/*
* Check if we need to send a sense buffer from
* the struct se_cmd in question.
@@ -2241,6 +2246,7 @@ static void target_complete_ok_work(struct work_struct *work)
if (cmd->scsi_status)
goto queue_status;
+treat_as_normal_read:
atomic_long_add(cmd->data_length,
&cmd->se_lun->lun_stats.tx_data_octets);
/*
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 9f9f5902af38..922a39f45abc 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -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,
};
/*
--
2.13.6
