This is the beginning of support for external snapshots. An external
snapshot is a read-only blobstore device (struct spdk_bs_dev) that can
be used as a blob's back device. Normally a blob will have no back
device (a normal blob), a zeroes back device (a thin provisioned blob),
or a blob back device (a clone blob). When a blob has an external
snapshot ("esnap") as its back device, it is called an esnap clone.
With this patch, esnap clones can be created but they are not yet
useful. Subsequent patches in the series will plumb the IO path, enable
various features, and allow lvol bdevs to be esnap clones.
Signed-off-by: Mike Gerdts <mgerdts@nvidia.com>
Change-Id: I29206b628a2b03b6386a88532565e228df988e0e
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/14969
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
ce67e0c787