[U-Boot] How to validate ext4load file size (not null)?

[brendan]

I have stored multiple device trees in my emmc (ext4 formatted) partition
and I want to load a certain device tree file from emmc, but if this fails
(i.e. the device tree file doesn't exist) it should default to a device tree
that is stored in memory. 

For example if I run this: 

I get a return of: if test <return from ext4load> != null; then run <boot
with device tree from ext4>; else run <nand read .dtb stored in memory>; fi

I have seen the 
 command however using the example above, if I did 
 it does not set the filename environment variable therefore I cannot check
the size as  always returns true.  

I have tried other if statements such as:
 and they have not given me the true/false check that I am after.  

Does uBoot offer functionality for what I am after?  or should I be
approaching it with a different method. 

Thanks 




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