reenable tagged queueing of VMware virtual disk.

[Shunsuke SHINOMIYA]

 Hi, 

 Tagged queueing feature of a VMware virtual disk connected with SCSI
has been disabled since the cam quirk was added.
# this quirk is needed to find the drive by SCSI HA.

 I modified this quirk to allow tagged queueing while finding out causes
of low disk performance. 
 This modification improve the throughput of the disk I/O on VMware ESX
Server 3, at least. (4MBps -> 18Mbps, by some easy measurements using dd).


I think following modification to be applicable to RELENG_[456] and MAIN.
I applied this patch to my RELENG_5 (virtual) box and do 'make -j4
buildworld' now and at present, the problem has not occurred. 

--- sys/cam/cam_xpt.c.orig      Fri Sep  8 18:10:14 2006
+++ sys/cam/cam_xpt.c   Fri Sep  8 17:43:57 2006
@@ -359,7 +359,7 @@
        {
                /* Does not support other than LUN 0 */
                { T_DIRECT, SIP_MEDIA_FIXED, "VMware*", "*", "*" },
-               CAM_QUIRK_NOLUNS, /*mintags*/0, /*maxtags*/0
+               CAM_QUIRK_NOLUNS, /*mintags*/2, /*maxtags*/255
        },

 thank you.

-- 
Shunsuke SHINOMIYA <shino at fornext.org>