On 05/10/2018 01:51 PM, Mike Christie wrote:
> On 05/09/2018 03:59 PM, Lee Duncan wrote:
>> 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);
>
>
> Do you want to return both the data and sense or just one or the other?
> Both right? In this code path we would return both the data and sense
> for drivers like iscsi.
>
> If the queue_data_in call a little below this line returns
> -ENOMEM/-EAGAIN then I think the queue full handling is going to end up
> only returning the sense like in your original bug. You would need a
> similar change to transport_complete_qf so it returns the data.
>
Oh yeah, one other question/comment. The above code is bypassing the
normal sense sending code so SCF_SENT_CHECK_CONDITION is not going to be
set. For iscsi could you end up where 2 paths complete the same command
because a reassign could race with one of these completions?
