1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
|
<think>
Okay, so I'm trying to figure out whether this QEMU bug is user-mode or system-mode related. The user compiled QEMU 0.15.1 and when they run it, the window stays black, uses 100% CPU, and can't be killed with Ctrl-C; they have to use killall -9. Strace shows it's waiting on a futex forever.
First, I need to understand what each mode entails. User-mode QEMU runs without needing root privileges because it uses software emulation for hardware components. System-mode, on the other hand, requires root access and uses KVM for virtualization, which interacts more deeply with the host system's hardware.
Looking at the build configuration: they enabled mixemu and io-thread, but disabled brlapi, opengl, etc. They have audio drivers set to oss, alsa, sdl. The issue is that QEMU isn't starting properly—black screen, high CPU usage, can't be killed normally.
The strace shows it's stuck on a futex, which suggests some kind of deadlock or waiting for a resource that's not being released. Since the user compiled it with certain options, maybe there's an issue in how QEMU is handling threads or resources in their setup.
Now, considering whether this is user-mode related: if QEMU was running in user mode, it wouldn't need root and would emulate hardware. If it's system mode, it uses KVM for better performance but requires more privileges. The fact that the window is black might point to a graphical issue, perhaps with SDL or other display drivers since OpenGL was disabled.
But wait, if they're using SDL as an audio driver, does that affect the display? Maybe not directly. The high CPU usage and futex suggests it's stuck in some loop or waiting on a resource that isn't being released properly. This could be related to how QEMU is handling threads or system calls, which might fall under system-mode if it's interacting with lower-level resources.
Alternatively, maybe the issue is in user mode because they're not using KVM, so it's pure emulation. But since it's stuck on a futex, perhaps there's an issue in how user-mode QEMU handles certain threading or synchronization primitives.
But I'm not entirely sure. I think that system-mode would involve more interactions with hardware and kernel modules, while user-mode is more about software-level issues. Since the problem seems to be within QEMU itself rather than interacting with external devices, it might lean towards user-mode. However, the high CPU usage and inability to terminate could also indicate a deeper issue that's system-related.
Hmm, but since they didn't mention needing root privileges or using KVM, maybe this is a user-mode bug because it's purely about QEMU's own execution without relying on kernel extensions. The futex issue might be related to how QEMU manages its internal threads and resources in user mode.
Wait, I'm confusing myself. Maybe I should think about what each mode does again. User-mode uses pure emulation, no KVM, runs as a regular user. System-mode uses KVM for hardware acceleration, needs root. In this case, the issue is happening when starting QEMU normally with "qemu", which is more likely to be in system-mode because sometimes people run it without specifying options and rely on KVM.
But if they didn't enable KVM, then maybe it's user-mode. Wait, looking back at their build config: I don't see --enable-kvm or anything like that. So perhaps they're running in user mode. Therefore, the bug would be related to user-mode QEMU.
Alternatively, even without KVM, if it's using some system resources, maybe it's still considered system-mode. But I think the key is whether QEMU is acting as a regular application (user) or needing special privileges and interacting with hardware more deeply (system).
Given that they didn't mention any issues with permissions or needing to run as root, and since the problem seems internal (black screen, high CPU), it's probably related to user-mode.
</think>
user
|