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.
Changes from v2:
- Cleaned up subject line and bug text formatting
- Removed unneeded inner braces
- Removed ugly goto
- Also updated the "queue full" path to handle this case
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 | 23 +++++++++++++++++++-
drivers/target/target_core_transport.c | 39 +++++++++++++++++++++++++++++-----
include/target/target_core_base.h | 1 +
3 files changed, 57 insertions(+), 6 deletions(-)
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 0d99b242e82e..a9656368a96d 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -689,8 +689,29 @@ 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 */
+ pr_debug("Tape FM/EOM/ILI status detected. Treat as normal read.\n");
+ 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..a15a9e3dce11 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2084,12 +2084,24 @@ 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 +2206,15 @@ 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 +2256,18 @@ 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,
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,
};
/*
--
2.16.3
--
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