PATCH : talloc-2.0.1 to add support for static talloc pools

[Karthick A R]

Hi,
 Please find attached a patch that would apply clean on top of talloc 2.0.1
that adds support for static talloc pools.
 I introduced a simple talloc static pool which creates a static pool of
fixed object sizes for a reclaimable object cache.
 The current talloc_pool is a variable sized pool where frees just decrement
the object count which is good if one wants to preallocate a large pool for
faster allocations.
 But I thought of adding another api that allows us to create a fixed size
cache. When all allocations are granted, it would fail instead of falling
back to malloc.(like the current pool)

 This enables one to create a talloc pool cache and then just use the
context pointer to allocate fixed size objects from the
 pre-created static cache. Because its a fixed-size pool cache, it supports
freeing objects to the pool as well.
 Allocations and free from the static pool add a bitmap overhead to keep
track of objects allocations and frees.
 But the existing talloc_pool header overhead remains unchanged. The
following apis were added:

+void *talloc_pool_cache(const void *context, size_t size, size_t objsize);
+void *talloc_cache(const void *context);
+void *talloc_cache_zero(const void *context);

talloc_cache just passed the context and expects to grab the static object
size for the pool. I haven't added any overhead to the talloc_chunk struct
as well to avoid impacting the current use-case on top of the talloc_pools.
A new TALLOC_FLAG_POOLCACHE has been added to track the allocations to the
static pool. This adds an extra bit the flag bit and hence also adjusts the
talloc magic base which currently has a 4 bit flag space accordingly.

Apart from the api additions, I have also fixed a crash when trying to use
nested talloc pools as currently that tries to free(tc) in case the tc or
the pool itself was allocated from another parent pool.

Eg:
   void *poolfoo = talloc_pool(parent, sizeof(struct foo) * 1024);
   void *poolbar = talloc_pool(poolfoo, sizeof(struct bar) * 100); /*
subpool*/

Trying to talloc_free(poolbar) would cause a crash currently. The patch also
addresses this by trying to trace the parent of the subpool to free the
subpool to the parent pool context.

Alternatively I have also forked the talloc 2.0.1 code base with the above
changes at my github repo:
https://github.com/karthick18/talloc

You can also trace the diff over 2.0.1 here :
https://github.com/karthick18/talloc/commit/d19bf7d298c276e38b988d00234ca8a8606db6e3

<https://github.com/karthick18/talloc/commit/d19bf7d298c276e38b988d00234ca8a8606db6e3>A
simple usage eg: for talloc in general which also includes usage for the
newly added apis can be traced here:
https://github.com/karthick18/talloc/blob/master/talloc_test.c

If you guys are ok with the patch, then maybe I can patch it on top of the
latest 2.0.5 talloc. This won't be required to get into Samba talloc anyway
but might be a good candidate to consider for the standalone LGPL super-COOL
talloc!

Regards,
-Karthick

<https://github.com/karthick18/talloc/blob/master/talloc_test.c>
-- 
-- 
Software is like sex: it's better when it's free.
-Linus Torvalds

A.R.Karthick
http://github.com/karthick18
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