User-friendly disk names [LWN.net]

User-friendly disk names

Posted Jun 27, 2011 3:33 UTC (Mon) by dlang (guest, #313)
In reply to: User-friendly disk names by mikov
Parent article: User-friendly disk names

Ok, I've seen PCI devices get identified in different orders after a kernel update, so I assumed that part of the identification depended on the order that things are scanned.

as for USB vs i2c, if you look at the low-level over-the-wire protocol, i believe that USB is really a superset of i2c. you can bit-bang a USB interface as well, (although not very efficiently), USB adds an additional layer of software and standard definitions over the raw wire protocol.

I could be mistake, but when I first learned about USB I was looking very closely at i2c for other things and I remembering that they were extremely similar at the hardware/signaling level

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User-friendly disk names

Posted Jun 27, 2011 4:12 UTC (Mon) by mikov (guest, #33179) [Link]

I have no doubt that you are correct about the i2c and USB similarity. If USB hubs are as dumb as you are describing, then the only way to identify a device is through some unique number (call it address, id, serial number, whatever). So you can't have two devices with the same USB serial number on the same bus. Exactly the same as i2c.

I think my point, to the extent that I even have a point beyond just being nostalgic about times when there was more direct control over hardware, is that in I2C there is no discovery. The device type is the device address. The devices and their ids are by definition fixed and known in advance. So, the question of identifying the physical location of a I2C device doesn't even exist. I2C is good for what it does.

With USB by contrast, you are identifying devices that look externally the same by a hidden magic serial number. There is a fundamental usability problem.

If I have two USB mouses which are _exactly_ the same, why do they need appear as separate devices to the computer? That makes no sense at all. If I plug them in the same PC at the same time, the only thing that really differentiates them is the USB connector.

Imagine a hypothetical product where users can interact with multiple virtual machines running on the same PC, using multiple video cards, mice and keyboards. It is pure idiocy to have to associate the keyboards and mice to the virtual machines by their unique USB serial number rather than the USB connector where they are plugged.

In other words, ideally USB hubs should have been designed to function like PCI-PCI bridges. Oh well, that is not a Linux problem :-)