[stgt] [PATCH 12/15] ssc: add variable-length block read support
Mark Harvey
markh794 at gmail.com
Thu Nov 13 00:52:43 CET 2008
On Tue, Nov 11, 2008 at 6:12 PM, FUJITA Tomonori
<fujita.tomonori at lab.ntt.co.jp> wrote:
> Very sorry for the late response.
No problems at all..
I've attempted to follow how the data is actually returned - but got lost.
I went back to looking/working at the SCSI PR. which is progressing
very slowly. Reading those standards just puts me to sleep :)
>
> On Fri, 31 Oct 2008 15:20:44 +1100
> "Mark Harvey" <markh794 at gmail.com> wrote:
>
>> On Mon, Oct 6, 2008 at 1:37 AM, FUJITA Tomonori
>> <fujita.tomonori at lab.ntt.co.jp> wrote:
>> > Signed-off-by: FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp>
>> > ---
>> > usr/bs_ssc.c | 43 ++++++++++++++++++++++++++++++++++++++-----
>> > 1 files changed, 38 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/usr/bs_ssc.c b/usr/bs_ssc.c
>> > index cbbca83..134c670 100644
>> > --- a/usr/bs_ssc.c
>> > +++ b/usr/bs_ssc.c
>> > @@ -318,13 +318,46 @@ static int space_blocks(struct scsi_cmd *cmd, int32_t count)
>> > return SAM_STAT_GOOD;
>> > }
>> >
>> > -/* Return error - util written */
>> > static int resp_var_read(struct scsi_cmd *cmd, uint8_t *buf, uint32_t length,
>> > - int *transferfed)
>> > + int *transferred)
>> > {
>> > - *transferfed = 0;
>> > - sense_data_build(cmd, ILLEGAL_REQUEST, ASC_INVALID_FIELD_IN_CDB);
>> > - return SAM_STAT_CHECK_CONDITION;
>> > + struct ssc_info *ssc = dtype_priv(cmd->dev);
>> > + int ret = 0, result = SAM_STAT_GOOD;
>> > +
>> > + length = min(length, get_unaligned_be24(&cmd->scb[2]));
>> > + *transferred = 0;
>> > +
>> > + if (length != ssc->c_blk->blk_sz) {
>> > + if (ssc->c_blk->blk_type == BLK_EOD)
>> > + sense_data_build(cmd, 0x40 | BLANK_CHECK,
>> > + NO_ADDITIONAL_SENSE);
>> > + else
>> > + sense_data_build(cmd, NO_SENSE, NO_ADDITIONAL_SENSE);
>> > +
>> > + length = min(length, ssc->c_blk->blk_sz);
>> > + result = SAM_STAT_CHECK_CONDITION;
>> > + scsi_set_in_resid_by_actual(cmd, length);
>> > +
>> > + if (!length)
>> > + goto out;
>> > + }
>> > +
>> > + ret = pread(cmd->dev->fd, buf, length,
>> > + ssc->c_blk->curr + sizeof(struct blk_header));
>> > + if (ret != length) {
>> > + sense_data_build(cmd, MEDIUM_ERROR, ASC_READ_ERROR);
>> > + result = SAM_STAT_CHECK_CONDITION;
>> > + goto out;
>> > + }
>> > + *transferred = length;
>> > +
>> > + ret = skip_next_header(cmd->dev);
>> > + if (ret) {
>> > + sense_data_build(cmd, MEDIUM_ERROR, ASC_READ_ERROR);
>> > + result = SAM_STAT_CHECK_CONDITION;
>> > + }
>> > +out:
>> > + return result;
>> > }
>> >
>> > static int resp_fixed_read(struct scsi_cmd *cmd, uint8_t *buf, uint32_t length,
>> > --
>> > 1.5.6.5
>> >
>> >
>>
>> First off, many thanks for completing the variable-block support.
>>
>> I'm finally in a position where I found some time to test all the
>> improvements and am stuck with this one. I don't fully understand the
>> return path.
>>
>> I performed a basic test by 'dd' a single 256k block to the tape
>> drive. I then tested what would happen if I tried to 'dd' a different
>> block size from the tape.
>>
>> Only a 'dd if=/dev/st0 bs=256k' would return any data.
>>
>> Included below is the trace I captured. Hopefully it is enough to
>> outline what I am seeing.
>> BTW: Testing on real tape drives, typically return '0+xx records out'
>>
>>
>> Any pointers as to where to start looking will be grateful.
>> Basically, it looks like any status except SAM_STAT_GOOD does not
>> return the payload.
>>
>> ============================
>> Write a single 256k block to tape...
>> # dd if=/dev/zero of=/dev/st0 bs=256k count=1
>> 1+0 records in
>> 1+0 records out
>> 262144 bytes (262 kB) copied, 0.0434786 s, 6.0 MB/s
>>
>> Confirm 'tape' contents contains a single 256k block..
>> # ./dump_tape -f /d/01/tape2
>> Media : tape2
>> type : Data
>> Media serial number : tape2_1225355078, created Thu Oct 30 19:24:38 2008
>>
>> Beginning of Tape(16): Capacity 500 MB, Blk No.: 0, prev 0, curr 0, next 1152
>> Uncompressed data(2): Blk No. 1, prev 0, curr 1152, next 263344, sz 262144
>> Filemark(64): Blk No. 2, prev 1152, curr 263344, next 263392, sz 0
>> End of Data(32): Blk No. 3, prev 263344, curr 263392, next 263392, sz 0
>>
>>
>> Now test we can read in a 256k block from the tape.
>> # dd if=/dev/st0 of=/tmp/block0 bs=256k count=1
>> 1+0 records in
>> 1+0 records out
>> 262144 bytes (262 kB) copied, 0.00424289 s, 61.8 MB/s
>>
>> Now test if we can read in a partial block (this fails returning no
>> data - we should have read in the 128k)
>> # dd if=/dev/st0 of=/tmp/block0 bs=128k count=1
>> dd: reading `/dev/st0': Input/output error
>> 0+0 records in
>> 0+0 records out
>> 0 bytes (0 B) copied, 0.00249643 s, 0.0 kB/s
>
> Sorry for my dumb question here:
>
> What should stgt return? The first 128 KB of the first block and no
> sense?
The amount of data requested should be returned. In this example, 128k.
The sense returned should be :NO SENSE | VALID | ILI (Illegal Length
Indicator) and the overrun values (size of data block - size of data
requested) filled in sense_buffer[3] -> sense_buffer[7].
>
>
>> Now test if we can read in a more then a block (this fails returning
>> no data - we should have read in the 256k)
>> # dd if=/dev/st0 of=/tmp/block0 bs=512k count=1
>> dd: reading `/dev/st0': Input/output error
>> 0+0 records in
>> 0+0 records out
>> 0 bytes (0 B) copied, 0.00705821 s, 0.0 kB/s
>
> stgt should return the whole first block without sense, right?
>
The amount of data successfully read should be returned. In this example, 128k.
The sense returned should be :NO SENSE | VALID | ILI (Illegal Length
Indicator) and the amount of data NOT successfully returned -> filled
in sense_buffer[3] -> sense_buffer[7]
On a side note (real world implementation):
NetBackup as part of its logic to determine if the media has valid
NetBackup data performs a :
- Request 64k data
- NetBackup expects to see only 1k returned with the sense | ILI set.
Otherwise it treats the media as something it did not create.
SSC3-r04a reads as follows (page 91): - note 'SILI == Supress Illegal
Length Indicator'
If the SILI bit is zero and an incorrect-length logical block is read,
CHECK CONDITION status shall be returned. The ILI and VALID bits shall
be set to one in the sense data and the additional sense code shall be
set to NO ADDITIONAL SENSE INFORMATION
Upon termination, the logical position shall be after the
incorrect-length logical block (end-of-partition side)
If the FIXED bit is one, the INFORMATION field shall be set to the
requested transfer length minus the actual number of logical blocks
read (not including the incorrect-length logical block).
If the FIXED bit is zero, the INFORMATION field shall be set to the
requested transfer length minus the actual logical block length.
Logical units that do not support negative values shall set the
INFORMATION field to zero if the overlength condition exists.
Cheers
Mark
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