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

[Brian Gerst]

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
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