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hyperv/storvsc: storvsc_io_done(): do not use CAM_SEL_TIMEOUT

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CAM_SEL_TIMEOUT was introduced in
https://reviews.freebsd.org/D7521 (r304251), which claimed:

"VM shall response to CAM layer with CAM_SEL_TIMEOUT to filter those
invalid LUNs. Never use CAM_DEV_NOT_THERE which will block LUN scan
for LUN number higher than 7."

But it turns out this is not correct:

I think what really filters the invalid LUNs in r304251 is that:
before r304251, we could set the CAM_REQ_CMP without checking
vm_srb->srb_status at all:
ccb->ccb_h.status |= CAM_REQ_CMP.

r304251 checks vm_srb->srb_status and sets ccb->ccb_h.status properly,
so the invalid LUNs are filtered.

I changed my code version to r304251 but replaced the CAM_SEL_TIMEOUT
with CAM_DEV_NOT_THERE, and I confirmed the invalid LUNs can also be
filtered, and I successfully hot-added and hot-removed 8 disks to/from
the VM without any issue.

CAM_SEL_TIMEOUT has an unwanted side effect -- see cam_periph_error():
For a selection timeout, we consider all of the LUNs on
the target to be gone. If the status is CAM_DEV_NOT_THERE,
then we only get rid of the device(s) specified by the
path in the original CCB.

This means: for a VM with a valid LUN on 3:0:0:0, when the VM inquires
3:0:0:1 and the host reports 3:0:0:1 doesn't exist and storvsc returns
CAM_SEL_TIMEOUT to the CAM layer, CAM will detech 3:0:0:0 as well: this
is the bug I reported recently:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=226583

PR:	226583
Reviewed by:	mav
MFC after:	1 week
Sponsored by:	Microsoft
Differential Revision:	https://reviews.freebsd.org/D14690
This commit is contained in:
Dexuan Cui 2018-04-10 18:05:02 +00:00
parent 32c434538a
commit 0d880ef422
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=332385
1 changed files with 1 additions and 14 deletions
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15
sys/dev/hyperv/storvsc/hv_storvsc_drv_freebsd.c
View File

@ -2173,20 +2173,7 @@ storvsc_io_done(struct hv_storvsc_request *reqp)
scsi_op_desc(cmd->opcode, NULL));
}
}
/*
* XXX For a selection timeout, all of the LUNs
* on the target will be gone. It works for SCSI
* disks, but does not work for IDE disks.
*
* For CAM_DEV_NOT_THERE, CAM will only get
* rid of the device(s) specified by the path.
*/
if (storvsc_get_storage_type(sc->hs_dev) ==
DRIVER_STORVSC)
ccb->ccb_h.status |= CAM_SEL_TIMEOUT;
else
ccb->ccb_h.status |= CAM_DEV_NOT_THERE;
ccb->ccb_h.status |= CAM_DEV_NOT_THERE;
} else {
ccb->ccb_h.status |= CAM_REQ_CMP;
}