Is it safe to call low level Darwin function on FileHandle?

I have the following code:

extension FileHandle {
    func readInto(_ buffer: inout [UInt8]) -> Int {
        buffer.withUnsafeMutableBytes {
            Darwin.read(fileDescriptor, $0.baseAddress, $0.count)
        }
    }
}

It can compile, but I wonder if this is supported since it's code in an app that is going to be submitted to App Store.

The reason I don't use read(upToCount:) or readData(ofLength:) is that I am reading possibly very large files by small chunks and don't want to let Swift runtime allocate small buffers repeatedly.