Re: Virtual FAT disk images

[Eric Blake]

On Thu, Sep 09, 2021 at 09:32:48AM +0200, Pascal wrote:
> up² :-)
> can someone just ping me to make me sure I'm posting on the qemu list ?

Your question is reaching the list, but this mail ought to be informative:

https://lists.gnu.org/archive/html/qemu-devel/2021-09/msg02463.html

In short, the fact that you are seeing performance penalties with the
vvfat driver is unsurprising, and it may be a sign of bigger bugs
lurking.  The lack of answers is more a sign that no one actively
participating on the list currently uses virtual FAT in any serious
manner, so you are taking on your own risk.

That said, if you'd like to debug it and submit patches, we'd be
grateful!

> 
> Le mar. 31 août 2021 à 09:24, Pascal <patatetom@gmail.com> a écrit :
> 
> > up :-)
> > nobody uses this feature of qemu?
> >
> > Le ven. 27 août 2021 à 11:11, Pascal <patatetom@gmail.com> a écrit :
> >
> >> hello everybody,
> >>
> >> virtual FAT disk image - *which is a convenient way to transfer files to
> >> the guest without having to activate its network* - seems to work very
> >> poorly with Windows : do you have the same difficulties?
> >>
> >> context : up to date archlinux, qemu 6.0.0, fresh installed windows 10
> >> 21H1.
> >>
> >> /usr/bin/qemu-system-x86_64 -accel kvm -machine q35 -m 1024 -device
> >> nec-usb-xhci -device usb-tablet -cpu qemu64,kvm=off -parallel null -serial
> >> mon:stdio -hda windows.disk -hdb fat:rw:/tmp/test/

There may be other less-risky ways for easily transferring files
between host and guest; I know in the past I have seen both p9 and MTP
file systems mentioned as approaches, although I do not have
experience with setting those up myself to give you a sample command
line.

> >>
> >> access to the E: drive is extremely slow and the system events report
> >> many storahci (129: reinit \device\RaidPort0 sent) and disk (153: I/O
> >> @0x3f on disk 1 \device\00000001f replayed) warnings.
> >>
> >> regards.
> >>
> >

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org