Re: On PATH_MAX

[Bas Wijnen]

On Tue, Nov 08, 2005 at 08:51:09AM -0700, Christopher Nelson wrote:
> > Not exactly.  If a server wants to support arbitrary long 
> > paths, it's not going to map the whole thing into its address 
> > space.  It'll accept a container capability and map parts of 
> > it in, unmapping other parts of it.
> 
> What mechanism allows it to map *parts* of a single transfer in?

There is no transfer of data, there is only transfer of the container
capability.  This capability gives access to a set of pages, which can be
mapped in or out of the address space when the process likes.

> > The problem that remains is that the operation can take very 
> > long.  If you have a 4GB filename (or the maximum 64 bit 
> > value), the server will have a lot of work checking it.  Then 
> > again, it's doing that on your provided scheduling time, so 
> > that should be no problem, as long as other requests are not 
> > delayed by it.
> 
> Sure, except that while it's working on YOUR request, it's not
> processing anyone else's request.

That's why I wrote "as long as other requests are not delayed by it".  This
means that it should *not* block processing of other requests, which can be
done in several ways.  In the end, it may be concluded that all this is too
complex, but it is certainly possible.

On Tue, Nov 08, 2005 at 05:18:53PM +0100, Michal Suchanek wrote:
> On 11/8/05, Christopher Nelson <address@hidden> wrote:
> > > And why does the server need to check the filename? In what way?
> >
> > Assuming that the server's service requires the filename (perhaps it is
> > a filesystem server, or perhaps it is a photo album server... Both
> > services are equivalent in this example.) then of course it has to
> > process the filename.  At some point someone has to actually process the
> > filename.  Otherwise there's no point in having it.
> 
> The name is for you to know what is in the file. The server does not
> need the name to know that.

The filesystem server does need to know the filename, since that is the entity
which names the file.  In any case, it doesn't really matter, this discussion
is about allowing unbound transfers in general, of which filenames are just an
example.

Thanks,
Bas

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