setUpChild

fn setUpChild(sync: *CancelRegion.Sync, options: struct {
    stdin_pipe: fd_t,
    stdout_pipe: fd_t,
    stderr_pipe: fd_t,
    dev_null_fd: fd_t,
    prog_pipe: fd_t,
    argv_buf: [:null]?[*:0]const u8,
    env_block: process.Environ.Block,
    PATH: []const u8,
    spawn: process.SpawnOptions,
}) ForkBailError {
    try setUpChildIo(
        sync,
        options.spawn.stdin,
        options.stdin_pipe,
        linux.STDIN_FILENO,
        options.dev_null_fd,
    );
    try setUpChildIo(
        sync,
        options.spawn.stdout,
        options.stdout_pipe,
        linux.STDOUT_FILENO,
        options.dev_null_fd,
    );
    try setUpChildIo(
        sync,
        options.spawn.stderr,
        options.stderr_pipe,
        linux.STDERR_FILENO,
        options.dev_null_fd,
    );

    switch (options.spawn.cwd) {
        .inherit => {},
        .dir => |cwd_dir| try fchdir(sync, cwd_dir.handle),
        .path => |cwd_path| {
            var cwd_path_buffer: [PATH_MAX]u8 = undefined;
            const cwd_path_posix = try pathToPosix(cwd_path, &cwd_path_buffer);
            try chdir(sync, cwd_path_posix);
        },
    }

    // Must happen after fchdir above, the cwd file descriptor might be
    // equal to prog_fileno and be clobbered by this dup2 call.
    if (options.prog_pipe != -1) try dup2(sync, options.prog_pipe, prog_fileno);

    if (options.spawn.gid) |gid| {
        switch (linux.errno(linux.setregid(gid, gid))) {
            .SUCCESS => {},
            .AGAIN => return error.ResourceLimitReached,
            .INVAL => return error.InvalidUserId,
            .PERM => return error.PermissionDenied,
            else => return error.Unexpected,
        }
    }

    if (options.spawn.uid) |uid| {
        switch (linux.errno(linux.setreuid(uid, uid))) {
            .SUCCESS => {},
            .AGAIN => return error.ResourceLimitReached,
            .INVAL => return error.InvalidUserId,
            .PERM => return error.PermissionDenied,
            else => return error.Unexpected,
        }
    }

    if (options.spawn.pgid) |pid| {
        switch (linux.errno(linux.setpgid(0, pid))) {
            .SUCCESS => {},
            .ACCES => return error.ProcessAlreadyExec,
            .INVAL => return error.InvalidProcessGroupId,
            .PERM => return error.PermissionDenied,
            else => return error.Unexpected,
        }
    }

    if (options.spawn.start_suspended) {
        switch (linux.errno(linux.kill(0, .STOP))) {
            .SUCCESS => {},
            .PERM => return error.PermissionDenied,
            else => return error.Unexpected,
        }
    }

    return execv(
        sync,
        options.spawn.expand_arg0,
        options.argv_buf.ptr[0].?,
        options.argv_buf.ptr,
        options.env_block,
        options.PATH,
    );
}