hi Amit,
even i dump entire XMP to file kXMP_NS_EXIF_Aux namespace is not there, that is the problem, couldn't figureout why.
it is available in photoshop.
<rdf:Description rdf:about=""
xmlns:aux="http://ns.adobe.com/exif/1.0/aux/">
<aux:SerialNumber>XXXXXXXXX</aux:SerialNumber>
<aux:Lens>EF400mm f/2.8L IS II USM</aux:Lens>
<aux:LensInfo>400/1 400/1 0/0 0/0</aux:LensInfo>
<aux:LensSerialNumber>XXXXXXXXX</aux:LensSerialNumber>
<aux:ApproximateFocusDistance>315/10</aux:ApproximateFocusDistance>
</rdf:Description>
Rest of the namespaces no problem i can read, write, modify etc with APi
Best,