[SSSD] [PATCH 0/4]: Actual memory cache implementation

Jan Zelený jzeleny at redhat.com
Fri Mar 16 13:25:34 UTC 2012


> On Thu, 2012-01-12 at 11:49 -0500, Simo Sorce wrote:
> > On Tue, 2012-01-10 at 14:33 -0500, Simo Sorce wrote:
> > > On Tue, 2012-01-10 at 10:15 -0500, Simo Sorce wrote:
> > > > > Sure, we can talk about it. I'm looking at it from the users'
> > > > > perspectives, who I think would generally expect (and be alright
> > > > 
> > > > with)
> > > > 
> > > > > the fast cache being emptied on service restart. Since we still
> > > > > have
> > > > 
> > > > the
> > > > 
> > > > > not-quite-as-fast persistent LDB cache, I think the gain isn't
> > > > > worth
> > > > 
> > > > the
> > > > 
> > > > > user confusion.
> > > > 
> > > > Ok, I think I can understand this, it will also simplify the code I
> > > > guess so I'll change the patch.
> > > 
> > > Attached new set of patches.
> > > 
> > > I changed the init code to always create a new cache file on restart,
> > > incidentally this also got rid of the stat() call, so that problem has
> > > been put to rest permanently :)
> > > 
> > > I also changed all functions to use errno_t as the return type in their
> > > declaration when they return a errno code.
> > > 
> > > I think all the suggestions seen in the thread so far have been
> > > implemented as requested at this point, with the exception of the part
> > > where I should implement and use new options as that required
> > > additional code instead of mere refactoring. I will add those features
> > > in a later rebase.
> > 
> > New revision.
> > 
> > I removed bootid from the cache file header, given we recreate the file
> > every time sssd restarts it was useles.
> > 
> > I replaced it with a seed, and made the seed used in the hash table
> > randomly regenerated every time the hash table is recreated.
> > 
> > This is used to avoid collision based attacks [1].
> > 
> > Simo.
> > 
> > [1] https://lwn.net/Articles/474912/
> 
> I started looking at these last night. I have yet to complete a full
> review, but I'm attaching a set of patches rebased atop the current
> master so several of us can start reviewing.

Ok, I finished the review. I am fine with these patches in general, I have just 
a few comments and/or questions:

Why only one hash table for both name and uidkey? I think using two would make 
things a little bit more simple and fast (of course a tradeoff would be 
slightly higher memory consumption).

responder/nss/nsssrv_mmap_cache.c:220
- this condition is unnecessarry because of the condition on line 208

responder/nss/nsssrv_mmap_cache.c:242
- the assignment is redundant

responder/nss/nsssrv_mmap_cache.c:275
- why this condition? I think the following while will cover it

responder/nss/nsssrv_mmap_cache.c:516
- sizeof(uint32_t) -> sizeof(h.status)

responder/nss/nsssrv_mmap_cache.c:517
- sizeof(uint32_t) -> sizeof(h.status)

responder/nss/nsssrv_mmap_cache.c:561
- shouldn't the umask better be 0133?

close vs. munmap
Just out of curiosity: does it matter which should be first? I found two places 
in the code where the order is different:

sss_client/nss_mc_common.c:146
responder/nss/nsssrv_mmap_cache.c:717



That's all from my side. As I've said, my comments are rather minor things and 
suggestions, so in general I give these patches a green light.

Thanks
Jan
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