writeSync

fn writeSync(sync: *CancelRegion.Sync, fd: fd_t, buffer: []const u8) File.Writer.Error!usize {
    while (true) {
        try sync.cancel_region.await(.nothing);
        const rc = linux.write(fd, buffer.ptr, buffer.len);
        switch (linux.errno(rc)) {
            .SUCCESS => return @intCast(rc),
            .INTR => {},
            .INVAL => |err| return errnoBug(err),
            .FAULT => |err| return errnoBug(err),
            .AGAIN => return error.WouldBlock,
            .BADF => return error.NotOpenForWriting, // Can be a race condition.
            .DESTADDRREQ => |err| return errnoBug(err), // `connect` was never called.
            .DQUOT => return error.DiskQuota,
            .FBIG => return error.FileTooBig,
            .IO => return error.InputOutput,
            .NOSPC => return error.NoSpaceLeft,
            .PERM => return error.PermissionDenied,
            .PIPE => return error.BrokenPipe,
            .CONNRESET => |err| return errnoBug(err), // Not a socket handle.
            .BUSY => return error.DeviceBusy,
            else => |err| return unexpectedErrno(err),
        }
    }
}