Gregory's ServerCall it 32 lines, that assert belongs somewhere else
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217 comments
 I think that's everything for day 13: * O_CREAT support for openat Next, in no particular order: * Flesh out files a bit more (e.g. enforce O_RDONLY) Once I get all of those done, it's time to write a blog post about it and resume other projects!  Ended up with some extra free time tonight and did a couple more syscalls: unlinkat, mkdirat Remaining filesystem-related syscalls are the stat family of calls, rmdirat (or AT_REMOVEDIR I guess), chmod/chown/chgrp, readlinkat, linkat, symlinkat, and utimensat. Implemented a bunch of openat flags this morning: RDONLY/WRONLY/RDWR is now enforced, and O_DIRECTORY, O_APPEND, O_TRUNC, and O_EXCL are now supported I chose to diverge from POSIX on O_DIRECTORY because I think it's kind of lame, but I could change my mind if this comes back to bite me when I start porting real-world software The cache currently serves just to make sure that there is a 1:1 correspondence between inode numbers and inode data structures (so that if several files hold a reference to the same inode they all remain in sync), it does not persist inodes after all references are released... yet. A broader cache system that keeps cached data in unused RAM is planned for the future.  Okay, about done for today. Summary of day 14 writing a Unix clone: New syscalls: exit, waitpid Improvements to openat: enforces read/write mode, supports O_DIRECTORY, O_APPEND, O_TRUNC, O_EXCL, and O_CLOEXEC Added an inode cache Optimized the MMU code for fork and process clean-up (still no CoW, though) And laid some groundwork for signals, which I have been dreading from the start. initramfs :D Simon Zeni ported the Helios EFI bootloader to the Bunnix boot protocol last night, so I'm doing some other boot improvements this morning to get EFI support upstreamed Left: old thinkpad w/legacy boot Both booted from the same flash drive :)  Goal for the end of the week is to have a pretty decent C environment with a shell and a decent spread of coreutils ported, probably a bourne shell derivative plus sbase. I'll port DOOM, too, if all of that is done before Saturday. Fleshed out libc a tiny bit more and tried to port some sbase utilities before calling it quits for today So, in the morning of day 17, I have three languages running in userspace: Hare, C, and C++ I will keep fleshing out libc and the necessary syscalls until we have a shell. I suspect there is another scheduler bug as well. Coming up soon: pipe(2), dup(2), fcntl(2)  @drewdevault Signals are okay, as long as you offer epoll with signal_fd to tame them! @drewdevault O_DIRECTORY even caused lots of discussion in the Filesystem working group of the POSIX standards committee. @mxk I haven't implemented fsync and presently all writes are committed to disk before write(2) et al returns to userspace, so I'm not sure. I might know more when I get to that. @drewdevault @bugaevc okay, yeah, that is reasonable.  @drewdevault @mxk guess it can be useful — for atomicity, or for reducing the number of file name lookups in find(1)/ftw(3) if readdir returns DT_UNKNOWN — to be able to open() a node first, then fstat it, and if it's a directory do one thing (look up something relative to it with *at()), and do another thing otherwise.  @drewdevault Thank you! FWIW, I did go look at https://sr.ht/~sircmpwn, but didn't see bunnix in the projects (quite possible that I missed it) or recent commits to it (just os/+bunnix commits to hare). @drewdevault why did you choose to implement openat and friends? I was planning to avoid them entirely for my toy system. @f4grx they're a better design, using O_DIRECTORY etc, imho. Particularly when it comes to implementing mountpoints. Simplifies things if you don't start from the assumption that you're always walking from the root @drewdevault ah, yes, mountpoints are a tree by themselves, at least in linux. I was trying hard to avoid that in my simplified and NuttX inspired design. I have to check if I can implement the simple traditional syscalls over the _at versions to avoid doing both, my target was embedded with limited storage. |
Block device files are now mounted, not that you can open them