Re: mmap on 9p broken in 6.4

[Robert Schwebel <r.schwebel@pengutronix.de>]

Christian,

On Thu, Jul 13, 2023 at 09:50:42AM +0200, Christian Schoenebeck wrote:
> > > Does adding QEMU option "multidevs=remap" [1] resolve it?
> > >
> > > [1] https://wiki.qemu.org/Documentation/9psetup#Starting_the_Guest_directly
> >
> > Unfortunately not:
> >
> > + exec ./platform-v7a/sysroot-host/bin/qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -smp 4 -m 1024M -nographic -no-reboot -net nic,netdev=net1 -netdev user,id=net1,hostfwd=tcp:127.0.0.1:27737-:22,hostfwd=tcp:127.0.0.1:12345-:12345 -rtc base=2000-01-01 -object rng-random,filename=/dev/random,id=rng0 -device vi
> > rtio-rng-device,rng=rng0 -device virtio-scsi-device,id=scsi -fsdev local,id=rootfs,path=./platform-v7a/root,security_model=mapped-file,multidevs=remap -device virtio-9p-device,fsdev=rootfs,mount_tag=/dev/root -kernel ./platform-v7a/images/linuximage -dtb ./platform-v7a/images/vexpress-v2p-ca9.dtb -append 'root=/dev/
> > root rootfstype=9p rootflags=trans=virtio console=ttyAMA0,115200 loglevel=5 systemd.show_status=auto'
>
> I don't see any cache option here. I would expect at least cache=mmap here:
>
> https://wiki.qemu.org/Documentation/9p_root_fs#Boot_the_9p_Root_FS_System
>
> By default it's cache=none, which means no mmap() would be allowed either.

This does help:

----------8<----------
+ exec ./platform-v7a/sysroot-host/bin/qemu-system-arm -machine vexpress-a9 -cpu cortex-a9 -smp 4 -m 1024M -nographic -no-reboot -net nic,netdev=net1 -netdev user,id=net1,ho
stfwd=tcp:127.0.0.1:27737-:22,hostfwd=tcp:127.0.0.1:12345-:12345 -rtc base=2000-01-01 -object rng-random,filename=/dev/random,id=rng0 -device virtio-rng-device,rng=rng0 -dev
ice virtio-scsi-device,id=scsi -fsdev local,id=rootfs,path=./platform-v7a/root,security_model=mapped-file,multidevs=remap -device virtio-9p-device,fsdev=rootfs,mount_tag=/de
v/root -kernel ./platform-v7a/images/linuximage -dtb ./platform-v7a/images/vexpress-v2p-ca9.dtb -append 'root=/dev/root rootfstype=9p rootflags=trans=virtio,cache=mmap conso
le=ttyAMA0,115200 loglevel=5 systemd.show_status=auto'
[    0.000000] L2C: platform modifies aux control register: 0x02020000 -> 0x02420000
[    0.000000] L2C: DT/platform modifies aux control register: 0x02020000 -> 0x02420000
[    0.004881] smp_twd: clock not found -2
[    0.793281] simple-pm-bus bus@40000000:motherboard-bus@40000000:iofpga@7,00000000: Failed to create device link (0x180) with dcc:tcrefclk
[    0.809253] simple-pm-bus bus@40000000:motherboard-bus@40000000:iofpga@7,00000000: Failed to create device link (0x180) with dcc:tcrefclk
[    0.879343] physmap-flash 48000000.psram: map_probe failed
[    1.267846] 9pnet_virtio: no channels available for device root

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| |_) / _ \ '_ \ / _` | | | | __| '__/ _ \| '_ \| \ \/ /
|  __/  __/ | | | (_| | |_| | |_| | | (_) | | | | |>  <
|_|   \___|_| |_|\__, |\__,_|\__|_|  \___/|_| |_|_/_/\_\
                 |___/

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|  _ \(_)___| |_ _ __ ___ | |/ (_) |_
| | | | / __| __| '__/ _ \| ' /| | __|
| |_| | \__ \ |_| | | (_) | . \| | |_
|____/|_|___/\__|_|  \___/|_|\_\_|\__|


OSELAS(R)-DistroKit-2019.12.0-00429-g57ffae760eb9 / v7a-2019.12.0-00429-g57ffae760eb9
ptxdist-2023.07.1/2023-07-11T19:56:50+0200

DistroKit login: root
root@DistroKit:~ mount / -o remount,rw
root@DistroKit:~ ldconfig
root@DistroKit:~
----------8<----------

However, the default behaviour has changed. With 6.3, mmap worked without
cache=mmap.

> Again, effective 9p mount options are always useful, e.g. `mount | grep 9p`

With the change:
/dev/root on / type 9p (rw,relatime,cache=mmap,access=client,trans=virtio)

Without the change:
/dev/root on / type 9p (rw,relatime,access=client,trans=virtio)

rsc
-- 
Pengutronix e.K.                           | Dipl.-Ing. Robert Schwebel  |
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