Re: [SPDK] Bdev claim and single writer semantics

[Walker, Benjamin <benjamin.walker at intel.com>]

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On Sat, 2018-04-28 at 21:30 +0000, Andrey Kuzmin wrote:
> While adding support for the shared access semantics seems to be
> pretty straightforward, I thought it reasonable to bring the issue up
> here first, looking for insights, comments, and objections. Please let
> me know if there are any or I can give a shot to a shared access
> patch.

On Sat, Apr 28, 2018, 02:06 Harris, James R <james.r.harris(a)intel.com> wrote:
> I’m wondering if we should just remove the safety check.  The original concern
> was to prevent the overwriting of metadata.  For example, an NVMe bdev
> contains a logical volume store – the lvol bdev module has claimed the bdev,
> opening and writing directly to the NVMe bdev could corrupt the metadata.
> 
> But I agree there are a lot of use cases where you may still want to allow
> this for one reason or another.  And the Linux kernel doesn’t try to prevent
> this – you can put an LVM PV/VG on a block device and then write zeroes to the
> underlying block device.  Same with using parted to put down a GPT and
> creating a partition.

Based on the behavior of other similar block stacks, I'm on board with just
entirely removing the check. I vote we entirely decouple claiming (building the
block device dependency tree) from descriptors (read/write permission checks).

Thanks,
Ben