AnyPS5/docs/dev/debt/libkernel_sys.md

libkernel_sys technical debt

Functional

• fchdir (libkernel_sys) changes the guest working directory to the descriptor's directory: on Windows through the path recorded when the descriptor was opened, on Linux through the /proc/self/fd link target. It returns EBADF for a descriptor that is not open and ENOTDIR for one that is not a directory. FreeBSD change_dir's search-permission check (EACCES) is not modelled, and a directory renamed after it was opened is still reached through the recorded path. Console behaviour is unverified
• openat (libkernel_sys) passes AT_FDCWD (-100) and absolute paths to open. Any other relative path is joined to the descriptor's host directory, found the same way as for fchdir, so guest path aliases and case-insensitive name matching do not apply to it, and a .. component is not kept inside the guest root. It returns EBADF for a descriptor that is not open and ENOTDIR for one that is not a directory. As with open, O_NOFOLLOW and O_NONBLOCK are ignored. PPSA99003 opens directory entries this way. Console behaviour is unverified
• pathconf (libkernel_sys) looks the path up as FreeBSD 11's kern_pathconf does (links followed, ENAMETOOLONG for a path of 1024 bytes or more or a component over 255) and returns the constants of FreeBSD 11's UFS ufs_pathconf for files and directories alike: _PC_LINK_MAX 32767, _PC_NAME_MAX 255, _PC_PATH_MAX and _PC_SYMLINK_MAX 1024, _PC_PIPE_BUF 512, _PC_CHOWN_RESTRICTED and _PC_NO_TRUNC 1, _PC_FILESIZEBITS 64, _PC_REC_MAX_XFER_SIZE -1, _PC_PRIO_IO and _PC_SYNC_IO 0. Whether the console's filesystems report the same is not verified. It throws for the names whose UFS value depends on the mount (_PC_ALLOC_SIZE_MIN, _PC_REC_INCR_XFER_SIZE, _PC_REC_MIN_XFER_SIZE, _PC_MIN_HOLE_SIZE), the kernel options (_PC_ACL_EXTENDED, _PC_ACL_PATH_MAX, _PC_ACL_NFS4, _PC_MAC_PRESENT) or the page size (_PC_REC_XFER_ALIGN), and on which UFS and vop_stdpathconf disagree (_PC_MAX_CANON, _PC_MAX_INPUT, _PC_VDISABLE, _PC_ASYNC_IO); other names fail with EINVAL
• mkdirat (libkernel_sys) passes AT_FDCWD (-100) and absolute paths to mkdir. Any other relative path is joined to the descriptor's host directory, found the same way as for fchdir, so guest path aliases and case-insensitive name matching do not apply to it, and a .. component is not kept inside the guest root. It returns EBADF for a descriptor that is not open and ENOTDIR for one that is not a directory. On Windows, mode is ignored. Console behaviour is unverified
• readlink (libkernel_sys) on Windows reads a symbolic link's target from its reparse data and returns it with / separators, only when the target is relative, as symlink creates them. A symbolic link with an absolute target and a junction throw, as a host path has no guest form. Any other reparse point throws too, where FreeBSD reports EINVAL for a file that is not a link
• readlinkat (libkernel_sys) passes AT_FDCWD (-100) and absolute paths to readlink. Any other relative path is joined to the descriptor's host directory, found the same way as for fchdir, so guest path aliases and case-insensitive name matching do not apply to it, and a .. component is not kept inside the guest root. It returns EBADF for a descriptor that is not open and ENOTDIR for one that is not a directory. Console behaviour is unverified
• fork (libkernel_sys) throws: creating a child process is not supported. PPSA19111 imports it and fails to load without it. Its engine calls fork in Posix_Daemonize, only with -daemonize, and in Platform_ShellExecute before execvp("xdg-open"), which the main menu's Previews button reaches, so pressing Previews ends in this throw. setsid fails with EPERM, as FreeBSD's does for a process group leader, since the guest is taken to lead its own process group (see kill). umask keeps the guest's mask (initially 022, masked to 07777) and returns the previous one, Linux named shared-memory creation applies it, but ordinary files are still created with the host process's mask