Re: [TUHS] Abstractions

It's always useful to talk about requirements as the first part of the design process. At the high level, how important is backwards compatibility? Is the problem of how support existing application in scope, or not? Or is the assumption that emulation libraries will always be sufficient. How about performance, either of applications using the new API, or applcications using the legacy API's? And what are the hardware platforms that this new set of abstractions going to target? Is the goal only to target small embedded systems? Mobile handsets? Desktop systems? Is it supposed to be able to scale to super computers? Are web front-ends that need to be able to accept thousands of incoming TCP connections per second, and then redirect those connections to application logic servers in scope? Solutions that involve being able to support intpret general SQL queries may not scale in terms of performance and the ability to support thousands of file descriptors in a single process. Backwards compatibility is why we have multiple asynchronous I/O interfaces --- from select, poll, epoll, kqueue, and io_uring. And the reason why we've had multiple asynchronus I/O interfaces over the decades is because the performance requirements have changed, and the capability of hardware interfaces for high performance I/O has changed; it's no longer about I/O ports and interrupts, but instead, having multiple request and response queues through memory mapped I/O, and the need to be able to use multiple CPU's and multiplexing multiple network or storage transactions across a single doorbell or system call. If all of this is out of scope, then the design process will be much simpler, and perhaps more elegant; but the resulting design will not be useful for many of the use cases where Linux is used today. And perhaps that's OK. On the other hand, one person's simple, elegant design is another person's toy that isn't fit for their purpose. IBM once said that part of Linux's power is that it scales from wrist watches to super computers. Is that in scope for this theoretical design question? - Ted