[Bugs] [Bug 1222126] New: DHT: lookup-unhashed feature breaks runtime compatibility with older client versions

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1222126

            Bug ID: 1222126
           Summary: DHT: lookup-unhashed feature breaks runtime
                    compatibility with older client versions
           Product: GlusterFS
           Version: mainline
         Component: distribute
          Severity: urgent
          Assignee: bugs at gluster.org
          Reporter: srangana at redhat.com
                CC: bugs at gluster.org, gluster-bugs at redhat.com,
                    jdarcy at redhat.com, nbalacha at redhat.com,
                    rgowdapp at redhat.com, sabansal at redhat.com,
                    spalai at redhat.com, vbellur at redhat.com
        Depends On: 1221747
            Blocks: 1222053



+++ This bug was initially created as a clone of Bug #1221747 +++

Description of problem:
With the feature http://review.gluster.org/#/c/7702/ the on disk layout would
now carry 0 in the first 4 bytes of the xattr trusted.glusterfs.dht. In
previous revisions this was set to 1 and the DHT code does a strict check on
the same.

As a result lookups would fail to read and throw layout errors, when older
clients are used against a 3.7 volume.

Version-Release number of selected component (if applicable):
3.7

How reproducible:
Always

Steps to Reproduce:
1. Access a gluster volume using client bits from 3.7
2. Create a directory
3. Access the created directory from a client using 3.6 client bits

Actual results:
Step 3 reports layout inconsistencies

Expected results:
Step 3 should not report layout inconsistencies

Additional info:
Fixing this has a few parts to it as follows,
- Do not set layout xattr with the commit-hash unless lookup-unhashed is set to
auto
- Do not allow older clients to connect if the above option is set
- Warn the administrator that setting lookup-unhashed to auto would cause older
clients to not function well with the volume


Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1221747
[Bug 1221747] DHT: lookup-unhashed feature breaks runtime compatibility
with older client versions
https://bugzilla.redhat.com/show_bug.cgi?id=1222053
[Bug 1222053] DHT: lookup-unhashed feature breaks runtime compatibility
with older client versions
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