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

[Stefan Hajnoczi]

On Tue, Nov 16, 2021 at 02:03:15AM +0000, Qi, Yadong wrote:
> > > 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.

Question for Jens and Christoph:

Is there a way for userspace to detect whether a Linux block device
supports SECDISCARD?

If not, then maybe a new sysfs attribute can be added:

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index cef1f713370b..c946ef49ac15 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -304,6 +304,7 @@ QUEUE_SYSFS_BIT_FNS(nonrot, NONROT, 1);
 QUEUE_SYSFS_BIT_FNS(random, ADD_RANDOM, 0);
 QUEUE_SYSFS_BIT_FNS(iostats, IO_STAT, 0);
 QUEUE_SYSFS_BIT_FNS(stable_writes, STABLE_WRITES, 0);
+QUEUE_SYSFS_BIT_FNS(secure_erase, SECERASE, 0);
 #undef QUEUE_SYSFS_BIT_FNS

 static ssize_t queue_zoned_show(struct request_queue *q, char *page)

Stefan

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