Re: [PATCH] Use direct I/O for loop devices

[Demi Marie Obenour <demi@invisiblethingslab.com>]

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On Thu, Aug 18, 2022 at 04:12:10PM +0200, Jan Beulich wrote:
> On 18.08.2022 16:04, Demi Marie Obenour wrote:
> > On Thu, Aug 18, 2022 at 09:02:11AM +0200, Jan Beulich wrote:
> >> On 17.08.2022 22:46, Demi Marie Obenour wrote:
> >>> --- a/tools/hotplug/Linux/block
> >>> +++ b/tools/hotplug/Linux/block
> >>> @@ -330,7 +330,7 @@ mount it read-write in a guest domain."
> >>>          else
> >>>            roflag=''
> >>>          fi
> >>> -        do_or_die losetup $roflag "$loopdev" "$file"
> >>> +        do_or_die losetup --direct-io=on $roflag "$loopdev" "$file"
> >>
> >> I guess you want to first check (maybe in tools/configure) that losetup
> >> actually supports that option. The old-ish one I'm looking at doesn't,
> >> according to its --help output at least.
> > 
> > What version are you referring to?
> 
> The tool itself doesn't recognize --version. It originates from
> util-linux 2.19.1 from all I can tell.

I see.  Qubes OS doesn’t need to support such old versions.  Are you
referring to 

> > In Qubes OS the current plan is to use a block “script” written in C, to
> > improve performance and (when combined with kernel patches) eliminate
> > race conditions.  This code could be made a wrapper for the C version.
> 
> Is this relevant here in some way I don't recognize, or did you say this
> only to provide some further background info?

If the C code becomes part of the toolstack it would avoid needing to
call into losetup.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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