> The problem is that anything you build on top of Unix will always be a second class citizen in the Unix world.
Is first-class support required? Even things as fundamental as executing programs (the elf loader, for example) can be a second-class citizen without users noticing.
> For example, suppose you want a database-like filesystem. Either you implement it in the kernel, and now your special apps barely work on anyone’s computers. Or you implement it in userspace - preferably as a library. And now your apps can run anywhere without special kernel features but the terminal, and all the other applications on the computer can’t / won’t understand your new abstraction.
So implement it in the kernel anyway (write the driver). How does having a whole new OS in which this particular filesystem is first-class help? It doesn't help your argument that all filesystem drivers, by your definitions, are second-class citizens, and no one cares.
I'm actually rather keen to know what downside there is for not trying out your new idea in an existing OS.
After all, if your new idea is any good the existing OSes will adopt it anyway making it pointless for newcomers to try your new OS.
This conversation is tricky because there are technical questions (what is in userland vs in kernel?). But the real question of whether something is a first class citizen is whether it’s part of the ecosystem, such that essentially all software can depend on it being available. The elf loader is clearly part of the Linux ecosystem, regardless of whether it’s in userland or kernel space. All shipped Linux software just assumes elf is part of the system. Zfs is not, even though you can apparently get it to run as a kernel module.
> I'm actually rather keen to know what downside there is for not trying out your new idea in an existing OS.
It might be more fun. It might be easier to experiment, since you don’t need to read or change as much code. And it might be easier to make a new community than it is to convince people in the existing community to take your patches seriously. - Eg like what happens in programming languages.
Long running software projects like Linux are conservative - and for good reason. But the result is that there’s a lot of potentially good OS ideas that Linux will never adopt at this point its lifecycle. (Eg, “What if everything wasn’t a file?” / “what if we formally verified all the code in the kernel?” / etc.)
Like every I-Love-Coding-But-My-Work-Is-Boring developer, I've toyed with various technical ideas. Some, like playing around with language design, actually have a usable release. Others, like "hey, I want to write my own operating system" frequently boot up and then never go anywhere.
And I agree with you - what would the experience be when (for example) the SQL RDBMS is the operating system? Maybe I'd like to try it out and see.
If you want to modify an existing OS to make your own, Linux is not as easy to start with than FreeBSD (I've had experience only with those two, as far as modification of the OS goes).
Sure, there's some nice hooks into the kernel, but FreeBSD just seems so much more cohesive and easier to understand (might be due to how well it is documented, maybe).
With all that said, I am definitely going to have my next experiment done on NetBSD, which differs substantially in that it is a Rump Kernel (https://en.wikipedia.org/wiki/Rump_kernel) which seems even easier to hook my own OS stuff into.
Maybe NetBSD is an option for you if you want to produce a new OS with a feature that cannot be seamlessly grafted onto an existing OS. Fair warning, I haven't actually tried this on NetBSD yet, but it looks more doable (to me, and I'm an amateur at kernel dev) than any of the existing alternatives.
Is first-class support required? Even things as fundamental as executing programs (the elf loader, for example) can be a second-class citizen without users noticing.
> For example, suppose you want a database-like filesystem. Either you implement it in the kernel, and now your special apps barely work on anyone’s computers. Or you implement it in userspace - preferably as a library. And now your apps can run anywhere without special kernel features but the terminal, and all the other applications on the computer can’t / won’t understand your new abstraction.
So implement it in the kernel anyway (write the driver). How does having a whole new OS in which this particular filesystem is first-class help? It doesn't help your argument that all filesystem drivers, by your definitions, are second-class citizens, and no one cares.
I'm actually rather keen to know what downside there is for not trying out your new idea in an existing OS.
After all, if your new idea is any good the existing OSes will adopt it anyway making it pointless for newcomers to try your new OS.