Re: [Qemu-devel] [PATCH] LUKS: support preallocation in qemu-img

[Max Reitz]

On 10.07.19 19:03, Maxim Levitsky wrote:
> preallocation=off and preallocation=metadata
> both allocate luks header only, and preallocation=falloc/full
> is passed to underlying file, with the given image size.
> 
> Note that the actual preallocated size is a bit smaller due
> to luks header.

Couldn’t you just preallocate it after creating the crypto header so
qcrypto_block_get_payload_offset(crypto->block) + size is the actual
file size?

> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1534951
> 
> Signed-off-by: Maxim Levitsky <address@hidden>
> ---
>  block/crypto.c | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)

Hm.  I would expect a preallocated image to read 0.  But if you just
pass this through to the protocol layer, it won’t read 0.

(In fact, I don’t even quite see the point of having LUKS as an own
format still.  It was useful when qcow2 didn’t have LUKS support, but
now it does, so...  I suppose everyone using the LUKS format should
actually be using qcow2 with LUKS?)

Max

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