Re: how to detect a 32 bit process on 64 bit kernel

[Michael S. Tsirkin]

Hello!
Quoting r. Brian Gerst (bgerst@xxxxxxxxxxxxx) "Re: how to detect a 32 bit process on 64 bit kernel":
> Michael S. Tsirkin wrote:
> 
> >Hello!
> >Quoting r. Christoph Hellwig (hch@xxxxxxxxxxxxx) "Re: how to detect a 32 
> >bit process on 64 bit kernel":
> >
> >>>If no - would not it make a sence to add e.g. a flag in the
> >>>task struct, to make it possible?
> >>
> >>The kernel code shouldn't know.  If your driver needs this information
> >>something is seriously wrong with it. 
> >
> >
> >A character driver I am working on gets passed a structure
> >from user space by implementing a write file operation.
> >The structure includes a pointer and so the format varies
> >between a 32 and 64 bit processes.
> 
> The most portable way to do this is to have the first member of the 
> structure be a 32-bit value containing the size of the structure.  This 
> can then be used to identify what the structure format is.  This also 
> has the advantage of future-proofing the interface (add a field?  no 
> problem, the new size can be checked for).  Just be very careful that 
> the size from userspace is not trusted (ie. only allow known sizes).
> 
> --
> 				Brian Gerst

The size wont be sufficient here since its variable size
(ends with an array).

Sure, I could also just ask everyone to pass pointers in a
packed long long, but either way it will break the applications.

Why wouldnt it make sence for struct task to have a bit that tells
me its a compat system?

MST
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