Re: POC: make mxidoff 64 bits

Hi，

I'm currently looking into the `SlruReadSwitchPageSlow` function and have a question regarding the expression `&state->buf.data + bytes_read` — 
I suspect the ampersand (&) here might be misused. Would you be able to help me verify this?

```
	while (bytes_read < BLCKSZ)
	{
		ssize_t		rc;

		rc = pg_pread(state->fd,
					  &state->buf.data + bytes_read,
					  BLCKSZ - bytes_read,
					  offset);
		if (rc < 0)
		{
			if (errno == EINTR)
				continue;
			pg_fatal("could not read file \"%s\": %m", state->fn);
		}
		if (rc == 0)
		{
			/* unexpected EOF */
			pg_log(PG_WARNING, "unexpected EOF reading file \"%s\" at offset %u, reading as zeros",
				   state->fn, (unsigned int) offset);
			memset(&state->buf.data + bytes_read, 0, BLCKSZ - bytes_read);
			break;
		}
		bytes_read += rc;
		offset += rc;
	}
```

```
		rc = pg_pread(state->fd,
					  &state->buf.data + bytes_read,
					  BLCKSZ - bytes_read,
					  offset);
memset(&state->buf.data + bytes_read, 0, BLCKSZ - bytes_read);
```

--
Regards,
Man Zeng
www.openhalo.org