[Bugs] [Bug 1158129] New: After readv, md-cache only checks cache times if read was empty

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1158129

            Bug ID: 1158129
           Summary: After readv, md-cache only checks cache times if read
                    was empty
           Product: GlusterFS
           Version: 3.6.0
         Component: core
          Severity: medium
          Assignee: bugs at gluster.org
          Reporter: pspencer at fields.utoronto.ca
                CC: bugs at gluster.org, gluster-bugs at redhat.com



Created attachment 951446
  --> https://bugzilla.redhat.com/attachment.cgi?id=951446&action=edit
Patch to correct possible error of md-cache skipping cache validation after
successful reads

When md-cache is handling a readv callback, its logic is to skip checking the
file's iatt (to see if it has changed since the time of the last cache) if
"op_ret != 0".

I suspect that is a mistake, and the intent was to skip only on error; for
other fops, op_ret is 0 on success and nonzero on error, and md-cache has the
same code for them.

For readv, though, op_ret is the number of bytes read, so it will normally be
positive except on EOF.

The attached patch changes "op_ret != 0" to "op_ret < 0" to skip the check only
when an error was returned.

(Or, if the intent was really to check cache validity only on an EOF condition
when op_ret is zero, then probably a comment to that effect should be added).

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