[Bugs] [Bug 1722977] New: ESTALE change in fuse breaks get_real_filename implementation

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1722977

            Bug ID: 1722977
           Summary: ESTALE change in fuse breaks get_real_filename
                    implementation
           Product: GlusterFS
           Version: mainline
            Status: NEW
         Component: posix
          Severity: high
          Assignee: bugs at gluster.org
          Reporter: madam at redhat.com
                CC: bugs at gluster.org
  Target Milestone: ---
    Classification: Community



Description of problem:

The change of ENOENT to ESTALE in the fuse bridge in
59629f1da9dca670d5dcc6425f7f89b3e96b46bf has broken the get_real_filename
implementation over fuse:

get_real_filename is implemented as a virtual extended attribute to help Samba
implement the case-insensitive but case preserving SMB protocol more
efficiently. It is implemented as a getxattr call on the parent directory with
the virtual key of "get_real_filename:<entryname>" by looking for a spelling
with different case for the provided file/dir name (<entryname>) and returning
this correct spelling as a result if the entry is found.

Originally (05aaec645a6262d431486eb5ac7cd702646cfcfb), the implementation used
the ENOENT errno to return the authoritative answer that <entryname> does not
exist in any case folding.

Now this implementation is actually a violation or misuse of the defined API
for the getxattr call which returns ENOENT for the case that the dir that the
call is made against does not exist and ENOATTR (or the synonym ENODATA) for
the case that the xattr does not exist.

This was not a problem until the gluster fuse-bridge was changed to do map
ENOENT to ESTALE in 59629f1da9dca670d5dcc6425f7f89b3e96b46bf, after which we
the getxattr call for get_real_filename returned an ESTALE instead of ENOENT
breaking the expectation in Samba.

(It is an independent problem that ESTALE should not leak out to user space but
is intended to trigger retries between fuse and gluster. My theory is that the
leaking happens because of the wrong use of ESTALE here: the parent directory
exists in this case, and there is nothing stale....) 

But nevertheless, the semantics seem to be incorrect here and should be
changed.


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

master and version 6


How reproducible:

Always.


Steps to Reproduce:

On a gluster fuse mount, run `getfattr -n
glusterfs.get_real_filename:file-that-does-not-exist
/path/to/fuse/mount/some-subdir`.


Actual results:

This shows the ESTALE error.


Expected results:

It shows ENONET.

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