I encountered an issue during do_fetch where it silently failed due to an OSError being thrown and ignored. The task completed successfully but no file was downloaded and do_unpack subsequently failed. In my case it was Errno 36 but I think any OSError/IOError would encounter this.

Adding a "raise" on line 1934 of bitbake/lib/bb/fetch2/__init__.py resolved my issue and let me figure out the real error (that my filename was way too long).

```
 except IOError as e:
     if e.errno in [errno.ESTALE]:
         logger.error("Stale Error Observed %s." % u)
         raise ChecksumError("Stale Error Detected")
-
+    raise
 except BBFetchException as e:
```
ref:
https://git.yoctoproject.org/poky/tree/bitbake/lib/bb/fetch2/__init__.py?id=bdd2b0fee18c43597efc3493b9ac9ace9ccf7959#n1930

Happy to send a one-line patch if this is desired but figured a bug was a better place to start to provide context.