Re: [qemu-web PATCH] Add a blog post about FUSE block exports

From: Hanna Reitz <hreitz@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org
Subject: Re: [qemu-web PATCH] Add a blog post about FUSE block exports
Date: Fri, 20 Aug 2021 09:56:54 +0200	[thread overview]
Message-ID: <46a68d5c-cfc1-e521-8c6b-90eb74c85ede@redhat.com> (raw)
In-Reply-To: <YR6FauCbECxehubc@stefanha-x1.localdomain>

On 19.08.21 18:23, Stefan Hajnoczi wrote:
> On Thu, Aug 19, 2021 at 12:25:01PM +0200, Hanna Reitz wrote:
>> This post explains when FUSE block exports are useful, how they work,
>> and that it is fun to export an image file on its own path so it looks
>> like your image file (in whatever format it was) is a raw image now.
>>
>> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
>> ---
>> You can also find this patch here:
>> https://gitlab.com/hreitz/qemu-web fuse-blkexport-v1
>>
>> My first patch to qemu-web, so I hope I am not doing anything overly
>> stupid here (adding SVGs with extremely long lines comes to mind)...
>> ---
>>   _posts/2021-08-18-fuse-blkexport.md       | 488 ++++++++++++++++++++++
>>   screenshots/2021-08-18-block-graph-a.svg  |   2 +
>>   screenshots/2021-08-18-block-graph-b.svg  |   2 +
>>   screenshots/2021-08-18-block-graph-c.svg  |   2 +
>>   screenshots/2021-08-18-block-graph-d.svg  |   2 +
>>   screenshots/2021-08-18-block-graph-e.svg  |   2 +
>>   screenshots/2021-08-18-root-directory.svg |   2 +
>>   screenshots/2021-08-18-root-file.svg      |   2 +
>>   8 files changed, 502 insertions(+)
>>   create mode 100644 _posts/2021-08-18-fuse-blkexport.md
>>   create mode 100644 screenshots/2021-08-18-block-graph-a.svg
>>   create mode 100644 screenshots/2021-08-18-block-graph-b.svg
>>   create mode 100644 screenshots/2021-08-18-block-graph-c.svg
>>   create mode 100644 screenshots/2021-08-18-block-graph-d.svg
>>   create mode 100644 screenshots/2021-08-18-block-graph-e.svg
>>   create mode 100644 screenshots/2021-08-18-root-directory.svg
>>   create mode 100644 screenshots/2021-08-18-root-file.svg
> Great! Two ideas:
>
> It would be nice to include a shoutout to libguestfs and mention that
> libguestfs avoids exposing the host kernel's file systems and partion
> code to untrusted disk images. If you don't mount the image then the
> FUSE export has similar security properties.

Oh, right!  Absolutely.

Though now I do wonder why one would actually want to use QEMU’s FUSE 
exports then...

Looks like the performance isn’t as bad as I claimed (for me around 
1.5G/s for reading/writing from/to a raw image on tmpfs), so perhaps 
that’s one point.  Another is probably that FUSE exports are better 
suited when you actually want access to the whole image.  I guess.

> This is a long blog post. One idea is to show a quickstart
> qemu-storage-daemon FUSE export command-line in the beginning before
> explaining all the details. That way people who just want to see what
> this is about can get an idea without learning all the background first.

Sounds good, will do.  Thanks!

Hanna