Re: [RFC] Use custom hash function with bcache

[sami wagiaalla <swagiaal at redhat dot com>]

On 08/16/2010 03:13 PM, Daniel Jacobowitz wrote:
> On Mon, Aug 16, 2010 at 10:10:41AM -0400, sami wagiaalla wrote:
> > This patch enables the use of custom hash and comparison functions
> > when adding elements to a bcache. The patch also introduces hash and
> > comparison functions which take into consideration only the relevant
> > properties of the psymbol.
>
> This patch makes me nervous because it's violating the invariants of
> the bcache.  Any time you get a psymbol from the bcache, it is going
> to have other fields that were not hashed somewhat random.  What are
> those ignored fields, and why do they not matter?  How about
> lifetimes, are they as long-lived as the bcache?

I only took into consideration the values which are set by 
add_psymbol_to_bcache. The assumption is that these are the only values 
that will make a difference since they are the only values available 
when calculating the hash.

> You compare name, value, language, domain, and class.  The mangled
> name is ignored; this assumes that there is only ever one mangled name
> per demangled name, with no documentation of why that's safe to
> assume.

Hmm, the demangled name can be added if this is not a correct 
assumption. I just wanted to avoid the redundant check, and 
language_specific part of the symbol.

  Section is ignored; if there are two definitions of a symbol
> with the same name in different sections but the same value otherwise,
> we'll never find out.  That could break overlays.

Section is set to 0 by add_psymbol_to_bcache