On Sun, May 29, 2022 at 10:20:05PM +0000, Rodrigo Martins wrote: > It was thus said that the Great Markus Wichmann once stated: > > And you fundamentally cannot change anything about the userspace of another > > program, at least not in UNIX. > > When I open file descriptors and exec(3) the new program inherits > those. Is that not chaning the userspace of another process? >
Program, not process. And no, it is changing the kernelspace of another program. For userspace, file descriptors are just numbers. They attain meaning only from the kernel interface. > It was thus said that the Great Markus Wichmann once stated: > > Having one special-case program is better than changing all the general > > ones, right? > > Sure is. Too bad the stdbuf(1) uses such a fragile mechanism. > Well, I cannot think of anything else they could have done. Fundamentally, setting environment variables and hoping the target program will interpret them correctly is about the extent of what an external filter is capable of, here. > What if instead of changing every program we changed the standard > library? We could make stdio line buffered by setting an environment > variable. > The problem you run into here is that there is more than one standard library, and indeed it is even thinkable that some programming language may shirk libc entirely. Golang has been trying their damndest at that for a long time, just didn't go all the way and still wanted to use libpthread. Haskell/GHC would be another candidate, as would be Pascal. The only way to roll out a change that would affect all programs at the same time would be a kernel update, but as discussed, this is a userspace problem to solve. Plus, the environment variable idea breaks with programs with elevated privilege, but that is probably a good thing here. Ciao, Markus
