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| author | Peter Maydell | 2018-06-30 18:30:09 +0200 |
|---|---|---|
| committer | Peter Maydell | 2018-06-30 18:30:09 +0200 |
| commit | e3800998e66c13b24d8cc8a06fdcc8d03cd408fc (patch) | |
| tree | 7a4eeaf3ce8c8c362403381ecc4f7bd6228105b0 /docs/devel | |
| parent | Merge remote-tracking branch 'remotes/stefanha/tags/tracing-pull-request' int... (diff) | |
| parent | docs: mention shared state protect for OOB (diff) | |
| download | qemu-e3800998e66c13b24d8cc8a06fdcc8d03cd408fc.tar.gz qemu-e3800998e66c13b24d8cc8a06fdcc8d03cd408fc.tar.xz qemu-e3800998e66c13b24d8cc8a06fdcc8d03cd408fc.zip | |
Merge remote-tracking branch 'remotes/armbru/tags/pull-monitor-2018-06-30' into staging
Monitor patches for 2018-06-30
# gpg: Signature made Sat 30 Jun 2018 17:22:12 BST
# gpg: using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg: aka "Markus Armbruster <armbru@pond.sub.org>"
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867 4E5F 3870 B400 EB91 8653
* remotes/armbru/tags/pull-monitor-2018-06-30:
docs: mention shared state protect for OOB
tests: iotests: drop some stderr line
monitor: flush qmp responses when CLOSED
monitor: rename *_pop_one to *_pop_any
chardev: comment details for CLOSED event
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'docs/devel')
| -rw-r--r-- | docs/devel/qapi-code-gen.txt | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt index 88a70e4d45..94a7e8f4d0 100644 --- a/docs/devel/qapi-code-gen.txt +++ b/docs/devel/qapi-code-gen.txt @@ -666,22 +666,27 @@ command: - They are executed in order, - They run only in main thread of QEMU, -- They have the BQL taken during execution. +- They run with the BQL held. When a command is executed with OOB, the following changes occur: - They can be completed before a pending in-band command, - They run in a dedicated monitor thread, -- They do not take the BQL during execution. +- They run with the BQL not held. OOB command handlers must satisfy the following conditions: -- It executes extremely fast, -- It does not take any lock, or, it can take very small locks if all - critical regions also follow the rules for OOB command handler code, +- It terminates quickly, - It does not invoke system calls that may block, - It does not access guest RAM that may block when userfaultfd is - enabled for postcopy live migration. + enabled for postcopy live migration, +- It takes only "fast" locks, i.e. all critical sections protected by + any lock it takes also satisfy the conditions for OOB command + handler code. + +The restrictions on locking limit access to shared state. Such access +requires synchronization, but OOB commands can't take the BQL or any +other "slow" lock. If in doubt, do not implement OOB execution support. |