On 2021-04-22 11:56 a.m., Douglas Gilbert wrote:
On 2021-04-22 4:42 a.m., Hannes Reinecke wrote:
On 4/21/21 11:58 PM, Douglas Gilbert wrote:
On 2021-04-21 5:10 p.m., Bart Van Assche wrote:
On 4/21/21 10:47 AM, Hannes Reinecke wrote:
+static inline bool scsi_result_is_good(struct scsi_cmnd *cmd)
+{
+ return (cmd->result == 0);
+}
Do we really need an inline function to compare an integer with zero? How
about open-coding this comparison in the callers of this function?
Please don't open code it. Please fix it!
Spot the difference:
static inline int scsi_status_is_good(int status)
{
/*
* FIXME: bit0 is listed as reserved in SCSI-2, but is
* significant in SCSI-3. For now, we follow the SCSI-2
* behaviour and ignore reserved bits.
*/
status &= 0xfe;
return ((status == SAM_STAT_GOOD) ||
(status == SAM_STAT_CONDITION_MET) ||
/* >>> ^^^^^^^^^^^^^^^^^^^^^^ <<< */
/* Next two "intermediate" statuses are obsolete in SAM-4 */
(status == SAM_STAT_INTERMEDIATE) ||
(status == SAM_STAT_INTERMEDIATE_CONDITION_MET) ||
/* FIXME: this is obsolete in SAM-3 */
(status == SAM_STAT_COMMAND_TERMINATED));
}
In sg3_utils' library I ignore the last three SAM_STATs. Not sure if ignoring
bit 0 is still required.
Without considering SAM_STAT_CONDITION_MET a good status, someone will be
scratching their head wondering why so many PRE-FETCH commands fail.
That command can be used when a sequence of READs to consecutive LBAs is
followed by a different (i.e. non-consecutive) READ. That last READ could
be preceded by PRE-FETCH(new_LBA, IMMED). Assuming there is processing
of the data from the consecutive LBAs to be done, when the time comes
for READ(new_LBA) the probability of its data being in the disk's cache is
increased.
That would be a change in behaviour.
Current code doesn't check for CONDITION_MET, so this change shouldn't do it,
neither. Idea was that this patchset shouldn't change the current behaviour.
While your argument might be valid, it definitely is a different story and
would need to be address with a different patchset.
Okay. May I suggest a "FIX_ME" comment? And again, please don't open code it.
In driver manuals Seagate often list the PRE-FETCH command as optional. As
in: pay us some extra money and we will put it in. That suggests to me some
big OEM likes PRE-FETCH. Where I found it supported in WDC manuals, they
didn't support the IMMED bit which sort of defeats the purpose of it IMO.
And PRE-FETCH has another (sneaky) use. You might think that when a LBA is
unmapped, then if its data is in the cache, it would be removed. So what
does SBC-4 say about reading unmapped LBAs (sbc4r22 4.7.4.4 table 10):
"user data set to a vendor-specific value that is not obtained from
any other LBA; and" (... place 0xff bytes in the PI)
Spot the weasel word: _other_ ! So it can read the former data in that
now unmapped LBA. So the second usage of PRE-FETCH is to prevent that.
Even more worryingly, it looks like PRE-FETCH may be needed after a
cryptographic erase (via the SANITIZE command)! SYNCHRONIZE CACHE only
talks about the write side of the cache, not removing stale read data.
Doug Gilbert
