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

[Joerg Schilling <schilling@fokus.fraunhofer.de>]

"Christopher Friesen" <cfriesen@nortel.com> wrote:

> Joerg Schilling wrote:
> > "Christopher Friesen" <cfriesen@nortel.com> wrote:
>
> >>There's nothing there that says the mapping cannot change with 
> >>time...just that it has to be unique.
> > 
> > 
> > If it changes over the runtime of a program, it is not unique from the
> > view of that program.
>
> That depends on what "uniquely identified" actually means.
>
> One possible definition is that at any time, a particular path maps to a 
> single unique st_ino/st_dev tuple.
>
> 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.

Well it is obvious that this is a requirement.

If Linux does device name mapping at high level but leaves the low level part
unstable, then the following coul happen:

Just think about a program that checks a file that is on a removable media.

This media is mounted via a vold service and someone removes the USB cable
and reinserts it a second later. The filesystem on the device will be mounted
on the same mount point but the device ID inside the system did change.

As a result, the file unique identification st_ino/st_dev is not retained 
and the program is confused.

Jörg

-- 
 EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
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