Before switching between AioContexts we need to make sure that we're
fully quiesced ("nb_requests == 0" for every client) when entering the
drained section. Otherwise, coroutines may be run in the wrong context
after the switch, leading to a number of critical issues.To accomplish this, we add ".drained_poll" to BlockDevOps and use it in the NBD server, along with ".drained_being" and "drained_end", to coordinate the quiescing of the server while entering a drained section. v2: - Use a bool for the value returned by .drained_poll [Kevin] - Change .drained_poll comment to reflect that the returned boolean value will be true if the device is still busy, or false otherwise - Drop yield_co_list and use recv_coroutine and read_yielding [Kevin] - Return "true" or "false" in nbd_drained_poll [Kevin] - Fix grammar in the commit message of patch 2 [Eric] Sergio Lopez (2): block-backend: add drained_poll nbd/server: Use drained block ops to quiesce the server block/block-backend.c | 7 ++- include/sysemu/block-backend.h | 4 ++ nbd/server.c | 82 +++++++++++++++++++++++++--------- 3 files changed, 71 insertions(+), 22 deletions(-) -- 2.26.2
