Re: [PATCH v6 01/33] main-loop.h: introduce qemu_in_main_thread()

[Paolo Bonzini]

On 2/1/22 10:08, Emanuele Giuseppe Esposito wrote:
> + *
> + * This function should never be used in the block layer, please
> + * instead refer to qemu_in_main_thread().


This function should never be used in the block layer, because unit 
tests, block layer tools and qemu-storage-daemon do not have a BQL.
Please instead refer to qemu_in_main_thread().

> +
> +/**
> + * qemu_in_main_thread: same as qemu_mutex_iothread_locked when
> + * softmmu/cpus.c implementation is linked. Otherwise this function
> + * checks that the current AioContext is the global AioContext
> + * (main loop).
> + *
> + * This is useful when checking that the BQL is held as a
> + * replacement of qemu_mutex_iothread_locked() usege in the
> + * block layer, since the former returns false when invoked by
> + * unit tests or other users like qemu-storage-daemon that end
> + * up using the stubs/iothread-lock.c implementation.
> + *
> + * This function should only be used in the block layer.
> + * Use this function to determine whether it is possible to safely
> + * access the block layer's globals.
> + */
> +bool qemu_in_main_thread(void);

I think the reference to qemu_mutex_iothread_locked() complicates 
things.  It's enough to explain the different policies in my opinion:

/**
 * qemu_in_main_thread: return whether it's possible to safely access
 * the global state of the block layer.
 *
 * Global state of the block layer is not accessible from I/O threads
 * or worker threads; only from threads that "own" the default
 * AioContext that qemu_get_aio_context() returns.  For tests, block
 * layer tools and qemu-storage-daemon there is a designated thread that
 * runs the event loop for qemu_get_aio_context(), and that is the
 * main thread.
 *
 * For emulators, however, any thread that holds the BQL can act
 * as the block layer main thread; this will be any of the actual
 * main thread, the vCPU threads or the RCU thread.
 *
 * For clarity, do not use this function outside the block layer.
 */

Paolo