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(-)
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2.26.2