RE: [PATCH 1/2] block:hdev: support BLKSECDISCARD

[Qi, Yadong]

> > Add a new option "secdiscard" for block drive. Parse it and record it
> > in bs->open_flags as bit(BDRV_O_SECDISCARD).
> >
> > Add a new BDRV_REQ_SECDISCARD bit for secure discard request from
> > virtual device.
> >
> > For host_device backend: implement by ioctl(BLKSECDISCARD) on real
> > host block device.
> > For other backend, no implementation.
> >
> > E.g.:
> >     qemu-system-x86_64 \
> >     ... \
> >     -drive
> file=/dev/mmcblk0p2,if=none,format=raw,discard=on,secdiscard=on,id=sd0 \
> >     -device virtio-blk-pci,drive=sd0,id=sd0_vblk \
> >     ...
> 
> I'm curious why there is explicit control over this feature (-drive
> secdiscard=on|off). For example, is there a reason why users would want to
> disable secdiscard on a drive that supports it? I guess there is no way to 
> emulate
> it correctly so secdiscard=on on a drive that doesn't support it produces an 
> error?

Yes. AFAIK, there is no way to emulate a "secure" discard. But it seems also 
hard to
detect whether a host drive support secdiscard unless it really perform a real
secdiscard. So I choose to add an option for user to enable it for virtual 
block.
There is an assumption that user knows whether host support secdiscard.


Best Regard
Yadong