On 13/09/21 15:10, Stefan Hajnoczi wrote:
On Wed, Sep 08, 2021 at 09:10:17AM -0400, Emanuele Giuseppe Esposito wrote:
Currently, block layer APIs like block-backend.h contain a mix of
functions that are either running in the main loop and under the
BQL, or are thread-safe functions and run in iothreads performing I/O.
The functions running under BQL also take care of modifying the
block graph, by using drain and/or aio_context_acquire/release.
This makes it very confusing to understand where each function
runs, and what assumptions it provided with regards to thread
safety.
We call the functions running under BQL "graph API", and
distinguish them from the thread-safe "I/O API".
Maybe "BQL" is clearer than "graph" because not all functions classified
as "graph" need to traverse/modify the graph.
Bikeshedding, I like it! :)
... on the other hand, qemu-storage-daemon does not have a BQL (see patch
1); "graph API" functions run from the main (monitor) thread.
The characteristic of the "graph API" is that they affect global state, so
another possibility could be "global state API". But is there any global
state apart from the BlockDriverState graph and the associated
BlockBackends?