[Bug 226583] FreeBSD VM on Hyper-V/Azure can't properly detected SCSI disk da2

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=226583

--- Comment #6 from commit-hook at freebsd.org ---
A commit references this bug:

Author: dexuan
Date: Tue Apr 10 18:05:03 UTC 2018
New revision: 332385
URL: https://svnweb.freebsd.org/changeset/base/332385

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

  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

Changes:
  head/sys/dev/hyperv/storvsc/hv_storvsc_drv_freebsd.c

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