svn commit: r186882 - head/sys/cam/scsi

[Warner Losh]

Author: imp
Date: Thu Jan  8 00:45:47 2009
New Revision: 186882
URL: http://svn.freebsd.org/changeset/base/186882

Log:
  Make it possible to override the number of retries for the CD media.
  When trying to read scratched or damaged CDs and DVDs, the default
  mechanism is sub-optimal.  Programs like ddrescue do much better if
  you turn off retries entirely, since their algorithms are designed
  scan big areas fast, then winnow the areas down.  Turning off retries
  speeds these programs up by as much as 20x, since the drive is able to
  'stream past' many small errors...
  
  The sysctl/tunable kern.cam.cd.retry_count controls this.  That
  defaults to '4' (for a total of 5 attempts).  Setting to 0 turns off
  all retry attempts.
  
  Reviewed by:	scottl@

Modified:
  head/sys/cam/scsi/scsi_cd.c

Modified: head/sys/cam/scsi/scsi_cd.c
==============================================================================
--- head/sys/cam/scsi/scsi_cd.c	Thu Jan  8 00:31:48 2009	(r186881)
+++ head/sys/cam/scsi/scsi_cd.c	Thu Jan  8 00:45:47 2009	(r186882)
@@ -292,6 +292,9 @@ static struct periph_driver cddriver =
 
 PERIPHDRIVER_DECLARE(cd, cddriver);
 
+#ifndef	CD_DEFAULT_RETRY
+#define	CD_DEFAULT_RETRY	4
+#endif
 #ifndef CHANGER_MIN_BUSY_SECONDS
 #define CHANGER_MIN_BUSY_SECONDS	5
 #endif
@@ -299,11 +302,15 @@ PERIPHDRIVER_DECLARE(cd, cddriver);
 #define CHANGER_MAX_BUSY_SECONDS	15
 #endif
 
+static int cd_retry_count = CD_DEFAULT_RETRY;
 static int changer_min_busy_seconds = CHANGER_MIN_BUSY_SECONDS;
 static int changer_max_busy_seconds = CHANGER_MAX_BUSY_SECONDS;
 
 SYSCTL_NODE(_kern_cam, OID_AUTO, cd, CTLFLAG_RD, 0, "CAM CDROM driver");
 SYSCTL_NODE(_kern_cam_cd, OID_AUTO, changer, CTLFLAG_RD, 0, "CD Changer");
+SYSCTL_INT(_kern_cam_cd, OID_AUTO, retry_count, CTLFLAG_RW,
+           &cd_retry_count, 0, "Normal I/O retry count");
+TUNABLE_INT("kern.cam.cd.retry_count", &cd_retry_count);
 SYSCTL_INT(_kern_cam_cd_changer, OID_AUTO, min_busy_seconds, CTLFLAG_RW,
 	   &changer_min_busy_seconds, 0, "Minimum changer scheduling quantum");
 TUNABLE_INT("kern.cam.cd.changer.min_busy_seconds", &changer_min_busy_seconds);
@@ -1454,7 +1461,7 @@ cdstart(struct cam_periph *periph, union
 			devstat_start_transaction_bio(softc->disk->d_devstat, bp);
 
 			scsi_read_write(&start_ccb->csio,
-					/*retries*/4,
+					/*retries*/cd_retry_count,
 					/* cbfcnp */ cddone,
 					MSG_SIMPLE_Q_TAG,
 					/* read */bp->bio_cmd == BIO_READ,