Read requests can now take vectored responses from the filesystem
implementation and send them to FUSE device via the writev() system call.
This allows file systems to send data without copying it into the
library-provided buffer if the data is already in memory.
The change also speeds up normal ReadFileOps as a side effect because
it removes extra memory allocations.
There's no reason for this to be enforced on the user. For use-cases such as S3-backing, there are no "permissions" of such to base this on. Consequently, everything ends up being owned as root and making it far more difficult to use.
It should, however, be optional.