Re: [dm-devel] [PATCH v2] dm-integrity: if we have discard support, use it when recalculating

[Melvin Vermeeren <vermeeren@vermwa.re>]

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Hi Milan,

On Tuesday, 11 May 2021 19:06:53 CEST Milan Broz wrote:
> Also, I added wiping to integritysetup because some tools (like mkfs)
> actually needef to read unitialized data before creating metadata - so
> without previous wipe it failed. (These are bugs in the tools, obviously: I
> plan to report these  unfortunately it never happened. Dunno if it is still
> the case.)

I can confirm a lot of tools still do this. Even `blkdiscard` probes for 
filesystems as a sanity check before discarding. So in order to efficiently 
initialise SSD without wiping, you need to dd zero to the start and end before 
running blkdiscard, or use --no-wipe with (pre-patch) recalculate.

Also, I did not realise the wiping is fully done from integritysetup 
userspace, this means the statement that this option would be useful as a new 
one is flawed, so then I agree the patch should be reverted.

It would be nice however if integritysetup from userspace has a native feature 
to wipe devices supporting discard with discards instead of writing (zeroes?), 
perhaps in the form of a --wipe-discard flag or similar, but that's for 
another day. :)

Cheers,

-- 
Melvin Vermeeren
Systems engineer

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