openat

fn openat(
    ev: *Evented,
    cancel_region: *CancelRegion,
    dir: fd_t,
    path: [*:0]const u8,
    flags: linux.O,
    mode: linux.mode_t,
) !fd_t {
    var mut_flags = flags;
    if (@hasField(linux.O, "LARGEFILE")) mut_flags.LARGEFILE = true;
    while (true) {
        const thread = try cancel_region.awaitIoUring();
        thread.enqueue().* = .{
            .opcode = .OPENAT,
            .flags = 0,
            .ioprio = 0,
            .fd = dir,
            .off = 0,
            .addr = @intFromPtr(path),
            .len = mode,
            .rw_flags = @bitCast(mut_flags),
            .user_data = @intFromPtr(cancel_region.fiber),
            .buf_index = 0,
            .personality = 0,
            .splice_fd_in = 0,
            .addr3 = 0,
            .resv = 0,
        };
        ev.yield(null, .nothing);
        const completion = cancel_region.completion();
        switch (completion.errno()) {
            .SUCCESS => return completion.result,
            .INTR, .CANCELED => {},
            .FAULT => |err| return errnoBug(err),
            .INVAL => return error.BadPathName,
            .BADF => |err| return errnoBug(err), // File descriptor used after closed.
            .ACCES => return error.AccessDenied,
            .FBIG => return error.FileTooBig,
            .OVERFLOW => return error.FileTooBig,
            .ISDIR => return error.IsDir,
            .LOOP => return error.SymLinkLoop,
            .MFILE => return error.ProcessFdQuotaExceeded,
            .NAMETOOLONG => return error.NameTooLong,
            .NFILE => return error.SystemFdQuotaExceeded,
            .NODEV => return error.NoDevice,
            .NOENT => return error.FileNotFound,
            .SRCH => return error.FileNotFound, // Linux when opening procfs files.
            .NOMEM => return error.SystemResources,
            .NOSPC => return error.NoSpaceLeft,
            .NOTDIR => return error.NotDir,
            .PERM => return error.PermissionDenied,
            .EXIST => return error.PathAlreadyExists,
            .BUSY => return error.DeviceBusy,
            // This can be triggered by file locking and TMPFILE, but those
            // flags are mutually exclusive.
            .OPNOTSUPP => return error.OperationUnsupported,
            .AGAIN => return error.WouldBlock,
            .TXTBSY => return error.FileBusy,
            .NXIO => return error.NoDevice,
            .ROFS => return error.ReadOnlyFileSystem,
            .ILSEQ => return error.BadPathName,
            else => |err| return unexpectedErrno(err),
        }
    }
}