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| author | Douglas Gilbert <dgilbert@interlog.com> | 2010-12-23 21:40:37 -0500 |
|---|---|---|
| committer | James Bottomley <James.Bottomley@suse.de> | 2011-01-24 12:21:39 -0600 |
| commit | 75c65a5edaa8b815c1428314eaf696788f1ebbdb (patch) | |
| tree | bdb28de023e48dcc0f848bf8fb55310a9caa0322 /Documentation/scsi | |
| parent | 4977c82504f58d7579acabd21688183eaa8768fb (diff) | |
| download | linux-75c65a5edaa8b815c1428314eaf696788f1ebbdb.tar.bz2 | |
[SCSI] scsi_mid_low_api.txt recommend resid usage
As discussed in a thread on this list titled:
"RFC: short reads on block devices"
this patch adds recommendations for LLDs to set resid
when there might be uncertainty about how much data
has been returned by a device.
This patch inline and attached] is against scsi-misc-2.6.git
Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Diffstat (limited to 'Documentation/scsi')
| -rw-r--r-- | Documentation/scsi/scsi_mid_low_api.txt | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/Documentation/scsi/scsi_mid_low_api.txt b/Documentation/scsi/scsi_mid_low_api.txt index df322c103466..5f17d29c59b5 100644 --- a/Documentation/scsi/scsi_mid_low_api.txt +++ b/Documentation/scsi/scsi_mid_low_api.txt @@ -1343,7 +1343,7 @@ Members of interest: underruns (overruns should be rare). If possible an LLD should set 'resid' prior to invoking 'done'. The most interesting case is data transfers from a SCSI target - device device (i.e. READs) that underrun. + device (e.g. READs) that underrun. underflow - LLD should place (DID_ERROR << 16) in 'result' if actual number of bytes transferred is less than this figure. Not many LLDs implement this check and some that @@ -1351,6 +1351,18 @@ Members of interest: report a DID_ERROR. Better for an LLD to implement 'resid'. +It is recommended that a LLD set 'resid' on data transfers from a SCSI +target device (e.g. READs). It is especially important that 'resid' is set +when such data transfers have sense keys of MEDIUM ERROR and HARDWARE ERROR +(and possibly RECOVERED ERROR). In these cases if a LLD is in doubt how much +data has been received then the safest approach is to indicate no bytes have +been received. For example: to indicate that no valid data has been received +a LLD might use these helpers: + scsi_set_resid(SCpnt, scsi_bufflen(SCpnt)); +where 'SCpnt' is a pointer to a scsi_cmnd object. To indicate only three 512 +bytes blocks has been received 'resid' could be set like this: + scsi_set_resid(SCpnt, scsi_bufflen(SCpnt) - (3 * 512)); + The scsi_cmnd structure is defined in include/scsi/scsi_cmnd.h |