On Mon, Nov 12, 2018 at 11:11 AM, Florian Weimer <fweimer@xxxxxxxxxx> wrote: > * Daniel Colascione: > >> What about off_t differences? Again, it doesn't matter. From the >> *kernel's* point of view, there's one width of offset parameter per >> system call per architecture. The library I'm proposing would expose >> this parameter literally. > > Does this mean the application author needs to know when to split an > off_t argument into two, and when to pass it as a single argument, and > when to insert dummy arguments for alignment, depending on the > architecture? No, I wouldn't make callers go to that trouble. I don't see any barrier to common-sense local data transformations. These transformations don't have external dependencies, after all. I want a thin interface to the kernel, but not so thin as to be a direct mapping onto register locations. I don't see value in that level of correspondence. >>> And that means you wouldn't get as much >>> decoupling from the C and POSIX standards -- both of which specify at >>> least part of those semantics -- as you want, and we would still be >>> having these arguments. For example, it would be every bit as >>> troublesome for liblinuxabi.so.1 to export set_robust_list as it would >>> be for libc.so.6 to do that. >> >> Why? Such an exported function would cause no trouble until called, >> and there are legitimate reasons for calling such a function. Not >> everyone, as mentioned, wants to write a program that relies on libc. > > For that use case, a machine-readable system call ABI specification is > the only reasonable approach: > The challenge here is to come up with a > uniform description of the system call interface for all architectures, This is another example in which we should remember the old aphorism that the perfect is the enemy of the good. There's no reason that the kernel couldn't simply provide a library with conventional functions exported in the conventional way doing the conventional things that functions do, one that would free users from relying on direct use of syscall(2). If this library were to interact with errno and cancelation properly, so much the better. There's no reason to avoid this work in favor of some theoretically-elegant abstract-function-description metadata-based approach that will likely never materialize. (Alternatively: just regard C as the uniform description language.) >> This stance in the paragraph I've quoted is another example of glibc's >> misplaced idealism. As I've elaborated elsewhere, people use signals >> for many purposes today. The current signals API is extremely >> difficult to use correctly in a process in which multiple unrelated >> components want to take advantage of signal-handling functionality. >> Users deserve a cleaner, modern, and safe API. It's not productive >> withhold improvements to the signal API and gate them on unrelated >> features like process handles merely because, in the personal >> judgement of the glibc maintainers, developers should use signals for >> fewer things. > > The two aren't unrelated. If you take asynchronous signals out of the > picture, the design becomes simpler and easier to use. The two features *are* unrelated. The design I've proposed works equally well for synchronous and asynchronous signals, and limiting it to synchronous signals doesn't simplify it. Even if it were the case that the design were simpler and easier to use when limited to synchronous signals --- which it isn't, unless you want to go in the SEH direction, which is more, not less complicated --- that wouldn't be a reason to block the work until some form of process handle landed. The objections I've seen have all essentially amounted to "we don't think people should use signals".
