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Re: [PATCH 0/3] block: Introduce the 'zeroes-co' driver to help security


From: Fam Zheng
Subject: Re: [PATCH 0/3] block: Introduce the 'zeroes-co' driver to help security reports
Date: Wed, 10 Mar 2021 14:24:23 +0000



On Wed, 10 Mar 2021 at 12:38, Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
On 3/10/21 1:32 PM, Fam Zheng wrote:
> On Wed, 10 Mar 2021 at 11:44, Philippe Mathieu-Daudé <philmd@redhat.com
> <mailto:philmd@redhat.com>> wrote:
>
>     Hi,
>
>     This is an alternative approach to changing null-co driver
>     default 'read-zeroes' option to true:
>     https://www.mail-archive.com/qemu-block@nongnu.org/msg80873.html
>     <https://www.mail-archive.com/qemu-block@nongnu.org/msg80873.html>
>
>     Instead we introduce yet another block driver with an explicit
>     name: 'zeroes-co'. We then clarify in secure-coding-practices.rst
>     that security reports have to be sent using this new driver.
>
>     The 2nd patch is RFC because I won't spend time converting the
>     tests until the first patch is discussed, as I already spent enough
>     time doing that in the previous mentioned series.
>
>     Regards,
>
>     Phil.
>
>     Philippe Mathieu-Daudé (3):
>       block: Introduce the 'zeroes-co' driver
>       tests/test-blockjob: Use zeroes-co instead of null-co,read-zeroes=on
>       docs/secure-coding-practices: Describe null-co/zeroes-co block drivers
>
>      docs/devel/secure-coding-practices.rst |   7 +
>      block/zeroes.c                         | 306 +++++++++++++++++++++++++
>
> Why not add another BlockDriver struct to block/null.c and set the
> read_zeroes field in the .bdrv_file_open callback? It would make the
> patch much simpler.

This is the first patch I wrote but then realized you are listed as
null-co maintainer, so you might be uninterested in having this new
driver in the same file. And declaring the prototypes public to
reuse them seemed overkill.


I posted a patch for block/null.c to add the same interface, just as an alternative to the first patch. 

I think we all agree that both zeroed and non-zeroed read mode will be supported going forward, the divergence is on approach:

a) -blockdev null-co:// | -blockdev null-co://,read-zeroes=off,

if we make read-zeroes=on the default.

b) -blockdev null-co:// | -blockdev zero-co://,

if we keep the current default of null-co://, but introduce zero-co:// which has a clearer interface.

Fam

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