Re: [PULL 23/29] ui & main loop: Redesign of system-specific main thread event handling

[David Woodhouse]

On Tue, 2024-12-31 at 21:22 +0100, Philippe Mathieu-Daudé wrote:
> 
> This change tidies up main thread management to be more flexible.
> 
>  * The qemu_main global function pointer is a custom function for the
>    main thread, and it may now be NULL. When it is, the main thread
>    runs the main Qemu loop. This represents the traditional setup.
>  * When non-null, spawning the main Qemu event loop on a separate
>    thread is now done centrally rather than inside the Cocoa UI code.
>  * For most platforms, qemu_main is indeed NULL by default, but on
>    Darwin, it defaults to a function that runs the CFRunLoop.
>  * The Cocoa UI sets qemu_main to a function which runs the
>    NSApplication event handling runloop, as is usual for a Cocoa app.
>  * The SDL UI overrides the qemu_main function to NULL, thus
>    specifying that Qemu's main loop must run on the main
>    thread.
>  * The GTK UI also overrides the qemu_main function to NULL.
>  * For other UIs, or in the absence of UIs, the platform's default
>    behaviour is followed.

When exiting an emulated Xen guest with <Ctrl-a x> on the console, I
now see:

(gdb) run
Starting program: /home/dwmw2/git/qemu/ball/qemu-system-x86_64 -display none 
-vga none -serial mon:stdio -machine q35 -accel 
kvm,xen-version=0x4000a,kernel-irqchip=split -smp 2 -kernel 
/home/dwmw2/avocado/data/cache/by_name/bzImage -append printk.time=0\ 
root=/dev/xvda\ console=ttyS0\ xen_emul_unplug=ide-disks\ 
xen_no_vector_callback\ noapic\ loglevel=0 -drive 
file=/home/dwmw2/avocado/data/cache/by_name/rootfs.ext4,if=none,snapshot=on,format=raw,id=drv0
 -device xen-disk,drive=drv0,vdev=xvda -device virtio-net-pci,netdev=unet 
-netdev user,id=unet,hostfwd=:127.0.0.1:0-:22

Starting syslogd: OK
Starting klogd: OK
Running sysctl: OK
Saving 256 bits of non-creditable seed for next boot
Starting network: OK
Starting dhcpcd...
no such user dhcpcd
dhcpcd-9.4.1 starting
no interfaces have a carrier
forked to background, child pid 111
Starting dropbear sshd: OK
# 
QEMU: Terminated
qemu-system-x86_64: ../block/block-backend.c:1290: blk_in_drain: Assertion 
`qemu_in_main_thread()' failed.

Thread 1 "qemu-system-x86" received signal SIGABRT, Aborted.
0x00007ffff5ffc724 in __pthread_kill_implementation () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff5ffc724 in __pthread_kill_implementation () at /lib64/libc.so.6
#1  0x00007ffff5fa3d1e in raise () at /lib64/libc.so.6
#2  0x00007ffff5f8b942 in abort () at /lib64/libc.so.6
#3  0x00007ffff5f8b85e in __assert_fail_base.cold () at /lib64/libc.so.6
#4  0x00007ffff5f9be47 in __assert_fail () at /lib64/libc.so.6
#5  0x0000555555abf911 in blk_in_drain (blk=0x555557ca6680)
    at ../block/block-backend.c:1290
#6  0x000055555593410c in xen_block_dataplane_stop (dataplane=0x555558982950)
    at ../hw/block/dataplane/xen-block.c:695
#7  0x000055555593441a in xen_block_dataplane_stop (dataplane=<optimized out>)
    at ../hw/block/dataplane/xen-block.c:689
#8  0x00005555555dfd5e in xen_block_disconnect
    (xendev=xendev@entry=0x55555880aa60, errp=<optimized out>)
    at ../hw/block/xen-block.c:172
#9  0x00005555555dfeca in xen_block_unrealize (xendev=0x55555880aa60)
    at ../hw/block/xen-block.c:282
#10 0x000055555578ef71 in xen_device_unrealize (dev=<optimized out>)
    at ../hw/xen/xen-bus.c:978
#11 0x0000555555bfe65f in notifier_list_notify (list=<optimized out>, data=0x0)
    at ../util/notify.c:39
#12 0x00007ffff5fa6461 in __run_exit_handlers () at /lib64/libc.so.6
#13 0x00007ffff5fa652e in exit () at /lib64/libc.so.6
#14 0x0000555555b523dc in qemu_default_main (opaque=opaque@entry=0x0)
#15 0x00005555555609c0 in main (argc=<optimized out>, argv=<optimized out>) at 
../system/main.c:76

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