doc/nvmf: update readme to include nqn definition

  Namespace Malloc1 2

~~~

#### NQN Formal Definition

NVMe qualified names or NQNs are defined in section 7.9 of the

[NVMe specification](http://nvmexpress.org/wp-content/uploads/NVM_Express_Revision_1.3.pdf). SPDK has attempted to

formalize that definition using [Extended Backus-Naur form](https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form).

SPDK modules use this formal definition (provided below) when validating NQNs.

~~~{.sh}

Basic Types

year = 4 * digit ;

month = '01' | '02' | '03' | '04' | '05' | '06' | '07' | '08' | '09' | '10' | '11' | '12' ;

digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' ;

hex digit = 'A' | 'B' | 'C' | 'D' | 'E' | 'F' | 'a' | 'b' | 'c' | 'd' | 'e' | 'f' | '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' ;

NQN Definition

NVMe Qualified Name = ( NVMe-oF Discovery NQN | NVMe UUID NQN | NVMe Domain NQN ), '\0' ;

NVMe-oF Discovery NQN = "nqn.2014-08.org.nvmexpress.discovery" ;

NVMe UUID NQN = "nqn.2014-08.org.nvmexpress:uuid:", string UUID ;

string UUID = 8 * hex digit, '-', 3 * (4 * hex digit, '-'), 12 * hex digit ;

NVMe Domain NQN = "nqn.", year, '-', month, '.', reverse domain, ':', utf-8 string ;

~~~

Please note that the following types from the definition above are defined elsewhere:

1. utf-8 string: Defined in [rfc 3629](https://tools.ietf.org/html/rfc3629).

2. reverse domain: Equivalent to domain name as defined in [rfc 1034](https://tools.ietf.org/html/rfc1034).

While not stated in the formal definition, SPDK enforces the requirement from the spec that the

"maximum name is 223 bytes in length". SPDK does not include the null terminating character when

defining the length of an nqn, and will accept an nqn containing up to 223 valid bytes with an

additional null terminator. To be precise, SPDK follows the same conventions as the c standard

library function [strlen()](http://man7.org/linux/man-pages/man3/strlen.3.html).

#### NQN Comparisons

SPDK compares NQNs byte for byte without case matching or unicode normalization. This has specific implications for

uuid based NQNs. The following pair of NQNs, for example, would not match when compared in the SPDK NVMe-oF Target:

nqn.2014-08.org.nvmexpress:uuid:11111111-aaaa-bbdd-ffee-123456789abc

nqn.2014-08.org.nvmexpress:uuid:11111111-AAAA-BBDD-FFEE-123456789ABC

In order to ensure the consistency of uuid based NQNs while using SPDK, users should use lowercase when representing

alphabetic hex digits in their NQNs.

### Assigning CPU Cores to the NVMe over Fabrics Target {#nvmf_config_lcore}

SPDK uses the [DPDK Environment Abstraction Layer](http://dpdk.org/doc/guides/prog_guide/env_abstraction_layer.html)