Re: [PATCH] PAG support only

[Muli Ben-Yehuda <mulix@mulix.org>]

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On Wed, May 14, 2003 at 10:54:36AM +0100, David Howells wrote:
> 
> Muli Ben-Yehuda wrote:
> 
> > > + * VFS session authentication token cache
> > ...
> >
> > If you know the type of the data, why keep it all in one binary blob,
> > instead of a struct? cache effects? 
> 
> No. We _don't_ know the type of the data. A filesystem entrusts us with a
> token to keep in the PAG on its behalf. However, since this is meant to be a
> generic mechanism, it's entirely dependent on the fs as to what's in
> the blob. 

But you do know the type of the data in the blob... it's char* fsname,
const void* key and const void* data, according to your code. 

You do

void* blob = kmalloc(fsname size + key size + data size)

memcpy(blob, fsname, fsname size)
memcpy(blob + fsname offset, key, key size)
mempcy(blob + fsname offset + key offset, data, data size)

I suggest

struct fsblob { 
       const char* fsname; 
       const void* key; 
       size_t keysize; 
       const void* data; 
       size_t datasize; 
}; 

struct fsblob b; 

b->fsname = kmalloc(fsname size)
memcpy(b->fsname, fsname, fsname size)

etc. 

Your method loses on additional complexity, and wins on
speed. However, unless it's really, really speed sensitive code, I
would go for KISS any day.

> > Nothing in this patch appears to be using it. You aren't taking a
> > reference to the token here, what's protecting it from disappearing
> > after the return and before the caller gets a chance to do something
> > with it?
> 
> Thanks. Fixed.

My pleasure. 
-- 
Muli Ben-Yehuda
http://www.mulix.org


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