Enable / disable the certain device features by specifying feature value and sector count value.

[JonghwanChoi]

There are many device features. To support these features, we have to add a lot of code.
This patch set enable / disable the certain device features by specifying feature value and sector count value.

example) ./smartctl -s features,0x64,0x2 /dev/sdb -> DSN control

Do not turn dangerous features on.Use with care.
This patch is quite useful for the FW developer.

[Christian Franke]

Of course this useful for FW developers - but possibly dangerous (disconnect or brick device, damage data) for our typical user audience.

I'm not yet sure whether we want such send arbitrary ATA commands functionality in smartctl. Please discuss on smartmontools-devel mailing list.

Review of patch is left for later.

[Alex Samorukov]

I think smartctl should not be a tool doing this. Some of my arguments:

1. User is not expecting that smartctl/smartd can do any hard and we are trying to avoid it as much as we can (e.g. by blacklisting some "known to be bad" commands on some controllers)

2. On some OS/controllers there is only limited interface (e.g. on Darwin, some raid-s) which simply not allowing to send anything but predefined commands, so it will not work anyway.

May be its could be some other binary in the same source.