librbd: Improved support for balanced and localized reads

[zhengchengyao]

Fixes: https://tracker.ceph.com/issues/43793
Signed-off-by: Zheng Yin zhengyin@cmss.chinamobile.com

Checklist

• References tracker ticket
• Updates documentation if necessary
• Includes tests for new functionality or reproducer for bug

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[dillaman]

Can you also create a new teuthology test case where you enable this feature (perhaps in just balance mode for simplicity) during an RBD xfstest/fsx test concurrent w/ the OSD thrasher; and set ceph osd require-osd-release octopus?

[zhengchengyao]

thanks @dillaman , I add read balance mode test case in test_librbd.

[dillaman]

Still need to modify ImageCtx::get_read_flags to return the current setting of ImageCtx::read_flags if not zero, else follow current logic for parent/snapshot read flags.

[zhengchengyao]

Sorry, I confused op_flags and read_flags, thanks.

[dillaman]

lgtm -- thx

[dillaman]

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