Re: [RFC PATCH V2 1/2] linux-user: add a plugin API to filter syscalls

[Ziyang Zhang <functioner@sjtu.edu.cn>]

On 10/28/25 19:17, Richard Henderson wrote:
>>
>> Thanks for the review.
>> Beyond the code style, are you open to accept such a functionality as part of API plugins?
>
> Yes.

Thank you for your agreement!

Considering that our ultimate goal is to enable QEMU to support all features
of Lorelei, the current syscall filter can only play a limited role.

Here are some features currently required by Lorelei:

1. We need to bypass checks such as `pageflags` in `accel/tcg/user-exec.c`.
This is because the host library may provide memory blocks to the guest
program, and these memory blocks cannot be recorded by the page tables
emulated by `qemu-user`. As a result, errors may occur when invoking syscalls
like `read/write`.

2. The `cpu_loop` should support recursive invocation and exit. This is
necessary when the host library needs to execute guest callbacks, and the
recursively invoked `cpu_loop` should be able to return after the
callback finishes.

3. Since the host library may create new threads and execute guest callbacks
within those threads, the `thread_cpu` is `NULL` when the callback is first
executed. Therefore, a mechanism is required to create a `CPUState` when
`thread_cpu` is NULL.

Do you have any suggestions about how to implement these features?