Commits on May 3, 2023

1. Remove dependency on GetScsiUvmPath from driver installation …

   Currently, when installing drivers on LCOW, we use GetScsiUvmPath to
   check if the VHD is already mounted, and if it is, we assume the drivers
   have already been installed, so we can skip doing it again. This check
   has a few problems:
   
   - It relies on GetScsiUvmPath, which assumes a single mount-point in the
     guest for a given VHD. This assumption is not safe to make in the face
     of future changes, where we could mount a device (or partitions on it)
     multiple times.
   - It assumes the disk has stayed attached the whole time after drivers
     were installed. This may be a safe assumption today, but can be
     fragile in the future.
   - It does not work in the case of a VHD containing multiple sets of
     drivers, or a VHD being changed/updated to newer content after first
     install. Again, this is safe given the current overall design today,
     but could break in the future.
   
   This change is still mostly a bandaid fix. Probably what is most correct
   is to track driver installation in something with state (the GCS) rather
   than using a separately invoked binary to do the in-guest install.
   However, this change does address the first issue above, removing the
   dependency on GetScsiUvmPath. I do this in the following way:
   
   - Change install-drivers to check if the overlay path exists already,
     and exit with a no-op if it does. This encodes the assumption that the
     overlay path will be consistent for a given driver set.
   - Change InstallDrivers in the shim to compute a V5 GUID from the VHD
     path, and use that as part of the overlay path given to the guest.
     This ensures there is a unique guest overlay path for each unique host
     driver VHD path.
   
   Signed-off-by: Kevin Parsons <kevpar@microsoft.com>

   

   kevpar committed May 3, 2023
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2. Remove dependency on GetScsiUvmPath from WCOW-isolated mounts …

   The WCOW-isolated SCSI mount process currently works as follows:
   - In resources_wcow.go, go through each mount on the OCI spec, and if it
     is a SCSI mount, add a mount to the UVM for it.
   - in hcsdoc_wcow.go, go through each mount on the OCI spec, use
     GetScsiUvmPath to determine the guest path it was mounted to, and add
     an entry to the container doc for it.
   
   This is quite hacky, as it relies on a 1:1 mapping between host VHDs and
   mounts in the guest, and also because it requires us to re-query
   information we've already been given. The SCSIMount object returned when
   we mounted to the guest can already tell us the guest path.
   
   This change resolves this problem by instead determing the set of guest
   mounts that should be added to the container doc at the time when the
   SCSI mounts are done, and saving it in the creation options. Then, when
   we construct the actual container doc, we just grab those mounts and add
   them in.
   
   Signed-off-by: Kevin Parsons <kevpar@microsoft.com>

   

   kevpar committed May 3, 2023
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