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7e8c182fb5
Simplify the way the aiocontext can be changed in a BDS graph. There are currently two problems in bdrv_try_set_aio_context: - There is a confusion of AioContext locks taken and released, because we assume that old aiocontext is always taken and new one is taken inside. - It doesn't look very safe to call bdrv_drained_begin while some nodes have already switched to the new aiocontext and others haven't. This could be especially dangerous because bdrv_drained_begin polls, so something else could be executed while graph is in an inconsistent state. Additional minor nitpick: can_set and set_ callbacks both traverse the graph, both using the ignored list of visited nodes in a different way. Therefore, get rid of all of this and introduce a new callback, change_aio_context, that uses transactions to efficiently, cleanly and most importantly safely change the aiocontext of a graph. This new callback is a "merge" of the two previous ones: - Just like can_set_aio_context, recursively traverses the graph. Marks all nodes that are visited using a GList, and checks if they *could* change the aio_context. - For each node that passes the above check, drain it and add a new transaction that implements a callback that effectively changes the aiocontext. - Once done, the recursive function returns if *all* nodes can change the AioContext. If so, commit the above transactions. Regardless of the outcome, call transaction.clean() to undo all drains done in the recursion. - The transaction list is scanned only after all nodes are being drained, so we are sure that they all are in the same context, and then we switch their AioContext, concluding the drain only after all nodes switched to the new AioContext. In this way we make sure that bdrv_drained_begin() is always called under the old AioContext, and bdrv_drained_end() under the new one. - Because of the above, we don't need to release and re-acquire the old AioContext every time, as everything is done once (and not per-node drain and aiocontext change). Note that the "change" API is not yet invoked anywhere. Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com> Message-Id: <20221025084952.2139888-3-eesposit@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> |
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| chardev | ||
| crypto | ||
| disas | ||
| exec | ||
| fpu | ||
| hw | ||
| io | ||
| libdecnumber | ||
| migration | ||
| monitor | ||
| net | ||
| qapi | ||
| qemu | ||
| qom | ||
| scsi | ||
| semihosting | ||
| standard-headers | ||
| sysemu | ||
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| ui | ||
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| elf.h | ||
| glib-compat.h | ||
| qemu-io.h | ||
| qemu-main.h | ||