I am using existing code, that passes data - union ibv_gid through TCP connection without converting the endianness. There is a comment inside: "The gid will be transfer byte by byte so no need to do "hton". The code is correct and works, but I don't understand why the data is passed byte by byte (actually they pass the entire struct) and why there is no need in endianess convertion. The data type they pass is:
union ibv_gid {
uint8_t raw[16];
struct {
uint64_t subnet_prefix;
uint64_t interface_id;
} global;
};
** For other data types (as int etc.) they do convert the data before and after
//VL_sock_sync_data function synchronizes between the two sides
//by exchanging data between the two sides.
//size bytes are being copied from out_buf to the other side, and being saved in in_buf.
rc = VL_sock_sync_data(sock_p, sizeof(union ibv_gid), &local_gid, &tmp_gid);
Can you please explain why there is no need in endianness conversion? Thank you for any help
The reasoning here seems to be that there's no need to do endianness conversion here because the GID (in its canonical representation) is not two 64-bit integers. It is 16 bytes.
The complication is that two systems with different endianness will see different values in the subnet_prefix and interface_id fields. So if they were to write those values to strings, send the strings back and forth, and compare them, that would be a problem. If they were to compare GIDs based on which one had a greater subnet_prefix, and expected the comparison to be the same between systems, that would be a problem. If one generated only consecutive interface_ids, and the other expected them to be consecutive, that would be a problem. But as long as they're only being used as opaque arrays of bytes, there's no problem.