Comment 21 for bug 1543046

OK, seems like commit c2e17ee973c59ca2b0898a147fa059c0c32369f4 may be required too:

    csys_fs::write: return -errno on write failure

    sysfs writes can fail for various reasons, and returning -errno is
    useful for indicating an error so that the caller can determine
    the best strategy to take if a sysfs write fails. This change
    is compatible with the current semantics, e.g. -ve is an error, but
    also propagates the errno back to the caller.

I'll get this resolved next week.