Re: CD writing in future Linux (stirring up a hornets' nest)

From: Christopher Friesen
Date: Fri Feb 10 2006 - 10:55:57 EST

Chris Shoemaker wrote:
On Fri, Feb 10, 2006 at 09:13:44AM -0600, Christopher Friesen wrote:

That depends on what "uniquely identified" actually means.

"The st_ino and st_dev fields taken together uniquely identify the
file within the system."

The other possibility (and this is what you seem to be advocating) is that a st_ino/st_dev tuple always maps to the same file over the entire runtime of the system.

However, I don't think this is a reasonable interpretation, and it's
clearly _not_ the one that Joerg is implying.

Joerg is claiming that the quoted sentence also implies that
_different_ st_ino/st_dev pairs will _always_ identify different
files. Taken in just the immediate context of stat.h, this is a
very reasonable interpretation.

It seems to me that "st_ino/st_dev tuple always maps to the same file" is equivalent to "different st_ino/st_dev pairs will always identify different files". What is the distinction between the two statements?

As I see it, the main question is whether it is a unique mapping *at one specific point in time*, or is it a unique mapping *for the duration of the system*? Note that in this case "system" includes "parts of the tree that may be remotely mounted from other machines on the network".

I would suggest that the spec doesn't specify the duration of the unique mapping, and thus as long as there is a unique mapping *at any particular point in time*, then there is no conflict.

If we read it as requiring a unique mapping for the duration of the system, consider a hypothetical "system" that includes all the devices of all the computers on the planet, and they are all dynamically appearing and disappearing continuously. Consider the technical challenge in ensuring that each file on this hypothetical system is permanently and uniquely identified by a device/inode pair.

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