Fast ack a flush to a RO volume. - #1962
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Add integration_test_just_read_one_downstairs, which creates three read-only downstairs, stops two of them, and confirms that a read-only upstairs can still activate and read from the remaining single downstairs. Also add a stop() helper to TestDownstairs so a test can bring an individual downstairs down while keeping the rest of the set running.
Augment integration_test_just_read_one_downstairs to manually send a flush after the first read, then confirm a second read completes successfully. With only one downstairs running, the flush still acks because the two stopped downstairs have their jobs moved to Skipped, so the flush is complete on all clients rather than hanging.
jmpesp
reviewed
Jul 24, 2026
| id: Uuid::new_v4(), | ||
| block_size: BLOCK_SIZE as u64, | ||
| sub_volumes: vec![], | ||
| read_only_parent: Some(Box::new( |
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Flushes won't be sent to read-only parents, you'll have to change the structure of the VCR to put this under sub volumes instead
A flush on a read-only volume has no data to persist, so ack it immediately in the guest Flush path instead of sending it to the downstairs. This broke a test, test_no_read_only_live_repair, which relied on a guest flush reaching the downstairs to retire skipped jobs after a fault. Retiring completed jobs still must happen, but in the production code the auto-flush will come around and clear these jobs out. The internal flush timer for the test framework is pinned to 24 hours, so to enable the internal flush we add a test-only BlockOp::FlushCheck and guest.flush_check() that runs the same work the automatic flush timer performs. Unlike a guest flush, this path still sends the flush to the downstairs on a read-only volume. Update the test to use it. This appears to be a simpler solution and does not require the heavier modification that enabling the auto flush on all tests would involve. Enabling auto-flush for all tests would add non-determinism to many tests that don't expect it.
leftwo
commented
Jul 27, 2026
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| if self.cfg.read_only { |
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This is the real change, the rest is to support the test changes.
leftwo
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jmpesp
approved these changes
Jul 27, 2026
| return; | ||
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| if self.cfg.read_only { |
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Maybe put a comment in for future us about how this doesn't affect the auto flush that the upstairs sends as part of the flush check?
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Added a test to verify that a read only volume that can connect to just one downstairs will be able to activate and read from that volume.
Shade was being thrown on Crucible, and this test was written in part to confirm that a single downstairs is all you need to talk to a RO volume.
quotes from the chat:
And
And
And
These slights were handled, and Crucible's good standing was returned.