Description taken from 8.x counterpart: https://bugzilla.redhat.com/show_bug.cgi?id=2313033

This BZ is being created to ensure that the fix also exists in a 7.x build.

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Description of problem:
We see that there is a gating mechanism to not allow Reads balancer to be enabled without "osd set-require-min-compat-client" to reef. But however, once we update the min-compat-client & enable upmap-read or read mode, we can change back the value of "osd set-require-min-compat-client" to older releases, and reads balancer would still perform primary balancing. 

This is not desired. There should be a gating mechanism to not allow users to revert back to older "osd set-require-min-compat-client" once they have enabled reads balancing on the cluster.

Snippets from the cluster. 

# ceph osd set-require-min-compat-client octopus
set require_min_compat_client to octopus

# ceph balancer status
{
    "active": true,
    "last_optimize_duration": "0:00:00.004260",
    "last_optimize_started": "Wed Sep 18 04:22:34 2024",
    "mode": "upmap",
    "no_optimization_needed": true,
    "optimize_result": "Unable to find further optimization, or pool(s) pg_num is decreasing, or distribution is already perfect",
    "plans": []
}
# ceph balancer mode upmap-read
Error EPERM: min_compat_client "octopus" < "reef", which is required for pg-upmap-primary. Try "ceph osd set-require-min-compat-client reef" before enabling this mode

# ceph osd set-require-min-compat-client reef
set require_min_compat_client to reef

# ceph balancer mode upmap-read

# ceph balancer status
{
    "active": true,
    "last_optimize_duration": "0:00:00.041342",
    "last_optimize_started": "Wed Sep 18 04:26:36 2024",
    "mode": "upmap-read",
    "no_optimization_needed": true,
    "optimize_result": "Optimization plan created successfully",
    "plans": []
}

# ceph osd set-require-min-compat-client octopus
set require_min_compat_client to octopus

Version-Release number of selected component (if applicable):
ceph version 19.1.1-47.el9cp (f7299ed699971b1ab459a410d1195d93ab38d13e) squid (rc)

How reproducible:
Always

Steps to Reproduce:
1. Deploy 8.0 Cluster. Update require_min_compat_client to reef. 
2. Enable Reads balancer module, set balancer mode to upmap-read. With this, we would start primary balancing in PGs.
3. Update require_min_compat_client to luminous. The command executes successfully. This should not happen. We should restrict the updation of min_compat_client to a lower release.

Actual results:
require_min_compat_client can be updated to lower ceph releases post changing balancer mode up upmap-read.

Expected results:
require_min_compat_client cannot be updated to lower release post changing balancer mode up upmap-read, and only higher releases should be allowed.

Additional info: