The SCSI PRE-FETCH (10 or 16) command is present both on hard disks
and some SSDs. It is useful when the address of the next block(s) to
be read is known but it is not following the LBA of the current READ
(so read-ahead won't help). It returns two "good" SCSI Status values.
If the requested blocks have fitted (or will most likely fit (when
the IMMED bit is set)) into the disk's cache, it returns CONDITION
MET. If it didn't (or will not) fit then it returns GOOD status.
The primary goal of this patch is to stop the SCSI subsystem treating
the CONDITION MET SCSI status as an error. The current state makes the
PRE-FETCH command effectively unusable via pass-throughs. The hunt to
find where the erroneous decision was made led to the
scsi_io_completion() function in scsi_lib.c . This is a complicated
function made more complicated by the intertwining of good and error
(or special case) processing paths.
Future work: if the sd driver was to use the PRE-FETCH command,
decide whether it and/or the block layer needs to know about the
two different "good" statuses. If so a mechanism would be needed
to do that.
ChangeLog to v2:
- further restructure the code, place some early non-zero
result processing in a new helper function:
scsi_io_completion_nz_result()
- this reduces the number of error checks on the zero result
path (the fast path) at the expense of some extra work for
the non-zero result processing
- rename some variables to make the code a little clearer
ChangeLog to v1:
- expand scsi_status_is_good() to check for CONDITION MET
- add another corner case in scsi_io_completion() adjacent
to the one for the RECOVERED ERROR sense key case. That
is another "non-error"
- structure code so extra checks are only on the error
path (i.e. when cmd->result is non-zero)
This patch is against mkp's 4.17/scsi-queue branch. It also applies
to lk 4.15.x where it was re-tested on a SAS SSD.
Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
drivers/scsi/scsi_lib.c | 140 +++++++++++++++++++++++++++++-------------------
include/scsi/scsi.h | 2 +
2 files changed, 87 insertions(+), 55 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index aea5a1ae318b..e1e974f08d52 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -738,6 +738,73 @@ static blk_status_t __scsi_error_from_host_byte(struct scsi_cmnd *cmd,
}
}
+/* Helper for scsi_io_completion() when cmd->result is non-zero. */
+static int scsi_io_completion_nz_result(struct scsi_cmnd *cmd,
+ blk_status_t *blk_statp)
+{
+ bool sense_valid;
+ bool about_current;
+ int result = cmd->result;
+ struct request *req = cmd->request;
+ struct scsi_sense_hdr sshdr;
+
+ sense_valid = scsi_command_normalize_sense(cmd, &sshdr);
+ about_current = sense_valid ? !scsi_sense_is_deferred(&sshdr) : true;
+
+ if (blk_rq_is_passthrough(req)) {
+ if (sense_valid) {
+ /*
+ * SG_IO wants current and deferred errors
+ */
+ scsi_req(req)->sense_len =
+ min(8 + cmd->sense_buffer[7],
+ SCSI_SENSE_BUFFERSIZE);
+ }
+ if (about_current)
+ *blk_statp = __scsi_error_from_host_byte(cmd, result);
+ } else if (blk_rq_bytes(req) == 0 && about_current) {
+ /*
+ * Flush commands do not transfers any data, and thus cannot use
+ * good_bytes != blk_rq_bytes(req) as the signal for an error.
+ * This sets the error explicitly for the problem case.
+ */
+ *blk_statp = __scsi_error_from_host_byte(cmd, result);
+ }
+ /*
+ * Recovered errors need reporting, but they're always treated as
+ * success, so fiddle the result code here. For passthrough requests
+ * we already took a copy of the original into sreq->result which
+ * is what gets returned to the user
+ */
+ if (sense_valid && (sshdr.sense_key == RECOVERED_ERROR)) {
+ /*
+ * if ATA PASS-THROUGH INFORMATION AVAILABLE skip
+ * print since caller wants ATA registers. Only occurs
+ * on SCSI ATA PASS_THROUGH commands when CK_COND=1
+ */
+ if ((sshdr.asc == 0x0) && (sshdr.ascq == 0x1d))
+ ;
+ else if (!(req->rq_flags & RQF_QUIET))
+ scsi_print_sense(cmd);
+ result = 0;
+ *blk_statp = BLK_STS_OK;
+ /* for passthrough, blk_stat may be set */
+ }
+ /*
+ * Another corner case: the SCSI status byte is non-zero but 'good'.
+ * Example: PRE-FETCH command returns SAM_STAT_CONDITION_MET when
+ * it is able to fit nominated LBs in its cache (and SAM_STAT_GOOD
+ * if it can't fit). Treat SAM_STAT_CONDITION_MET and the related
+ * intermediate statuses (both obsolete in SAM-4) as good.
+ */
+ if (status_byte(result) && scsi_status_is_good(result)) {
+ result = 0;
+ /* for passthrough error may be set */
+ *blk_statp = BLK_STS_OK;
+ }
+ return result;
+}
+
/*
* Function: scsi_io_completion()
*
@@ -772,33 +839,23 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
int result = cmd->result;
struct request_queue *q = cmd->device->request_queue;
struct request *req = cmd->request;
- blk_status_t error = BLK_STS_OK;
+ blk_status_t blk_stat = BLK_STS_OK; /* enum, BLK_STS_OK is 0 */
struct scsi_sense_hdr sshdr;
- bool sense_valid = false;
- int sense_deferred = 0, level = 0;
+ bool sense_valid_and_current = false;
+ int level = 0;
enum {ACTION_FAIL, ACTION_REPREP, ACTION_RETRY,
ACTION_DELAYED_RETRY} action;
unsigned long wait_for = (cmd->allowed + 1) * req->timeout;
if (result) {
- sense_valid = scsi_command_normalize_sense(cmd, &sshdr);
- if (sense_valid)
- sense_deferred = scsi_sense_is_deferred(&sshdr);
+ /* sense not about current command is termed: deferred */
+ if (scsi_command_normalize_sense(cmd, &sshdr) &&
+ !scsi_sense_is_deferred(&sshdr))
+ sense_valid_and_current = true;
+ result = scsi_io_completion_nz_result(cmd, &blk_stat);
}
if (blk_rq_is_passthrough(req)) {
- if (result) {
- if (sense_valid) {
- /*
- * SG_IO wants current and deferred errors
- */
- scsi_req(req)->sense_len =
- min(8 + cmd->sense_buffer[7],
- SCSI_SENSE_BUFFERSIZE);
- }
- if (!sense_deferred)
- error = __scsi_error_from_host_byte(cmd, result);
- }
/*
* __scsi_error_from_host_byte may have reset the host_byte
*/
@@ -816,13 +873,6 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
BUG();
return;
}
- } else if (blk_rq_bytes(req) == 0 && result && !sense_deferred) {
- /*
- * Flush commands do not transfers any data, and thus cannot use
- * good_bytes != blk_rq_bytes(req) as the signal for an error.
- * This sets the error explicitly for the problem case.
- */
- error = __scsi_error_from_host_byte(cmd, result);
}
/* no bidi support for !blk_rq_is_passthrough yet */
@@ -836,40 +886,20 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
"%u sectors total, %d bytes done.\n",
blk_rq_sectors(req), good_bytes));
- /*
- * Recovered errors need reporting, but they're always treated as
- * success, so fiddle the result code here. For passthrough requests
- * we already took a copy of the original into sreq->result which
- * is what gets returned to the user
- */
- if (sense_valid && (sshdr.sense_key == RECOVERED_ERROR)) {
- /* if ATA PASS-THROUGH INFORMATION AVAILABLE skip
- * print since caller wants ATA registers. Only occurs on
- * SCSI ATA PASS_THROUGH commands when CK_COND=1
- */
- if ((sshdr.asc == 0x0) && (sshdr.ascq == 0x1d))
- ;
- else if (!(req->rq_flags & RQF_QUIET))
- scsi_print_sense(cmd);
- result = 0;
- /* for passthrough error may be set */
- error = BLK_STS_OK;
- }
-
/*
* special case: failed zero length commands always need to
* drop down into the retry code. Otherwise, if we finished
* all bytes in the request we are done now.
*/
- if (!(blk_rq_bytes(req) == 0 && error) &&
- !scsi_end_request(req, error, good_bytes, 0))
+ if (!(blk_rq_bytes(req) == 0 && blk_stat) &&
+ !scsi_end_request(req, blk_stat, good_bytes, 0))
return;
/*
* Kill remainder if no retrys.
*/
- if (error && scsi_noretry_cmd(cmd)) {
- if (scsi_end_request(req, error, blk_rq_bytes(req), 0))
+ if (blk_stat && scsi_noretry_cmd(cmd)) {
+ if (scsi_end_request(req, blk_stat, blk_rq_bytes(req), 0))
BUG();
return;
}
@@ -881,7 +911,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
if (result == 0)
goto requeue;
- error = __scsi_error_from_host_byte(cmd, result);
+ blk_stat = __scsi_error_from_host_byte(cmd, result);
if (host_byte(result) == DID_RESET) {
/* Third party bus reset or reset for error recovery
@@ -889,7 +919,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
* happens.
*/
action = ACTION_RETRY;
- } else if (sense_valid && !sense_deferred) {
+ } else if (sense_valid_and_current) {
switch (sshdr.sense_key) {
case UNIT_ATTENTION:
if (cmd->device->removable) {
@@ -925,18 +955,18 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
action = ACTION_REPREP;
} else if (sshdr.asc == 0x10) /* DIX */ {
action = ACTION_FAIL;
- error = BLK_STS_PROTECTION;
+ blk_stat = BLK_STS_PROTECTION;
/* INVALID COMMAND OPCODE or INVALID FIELD IN CDB */
} else if (sshdr.asc == 0x20 || sshdr.asc == 0x24) {
action = ACTION_FAIL;
- error = BLK_STS_TARGET;
+ blk_stat = BLK_STS_TARGET;
} else
action = ACTION_FAIL;
break;
case ABORTED_COMMAND:
action = ACTION_FAIL;
if (sshdr.asc == 0x10) /* DIF */
- error = BLK_STS_PROTECTION;
+ blk_stat = BLK_STS_PROTECTION;
break;
case NOT_READY:
/* If the device is in the process of becoming
@@ -999,7 +1029,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
scsi_print_command(cmd);
}
}
- if (!scsi_end_request(req, error, blk_rq_err_bytes(req), 0))
+ if (!scsi_end_request(req, blk_stat, blk_rq_err_bytes(req), 0))
return;
/*FALLTHRU*/
case ACTION_REPREP:
diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index cb85eddb47ea..eb7853c1a23b 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -47,6 +47,8 @@ static inline int scsi_status_is_good(int status)
*/
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 */
--
2.14.1
