On 01/25/2012 09:38 AM, Daniel P. Berrange wrote:
-static unsigned long virCgroupPidCode(const void *name) +static int32_t virCgroupPidCode(const void *name, int32_t seed) { - return (unsigned long)name; + unsigned long pid = (unsigned long)name; + return virHashCodeGen(&pid, sizeof(pid), seed);
I'm not sure if it matters, but you could shorten these two lines to just one:
return virHashCodeGen(&name, sizeof(unsigned long), seed);
I actually preferred the slightly more verbose style, to make it clearer that we're actually passing in the PID as an int, cast to a pointer, instead of an int pointer.
And given the recent thread about mingw32, this is wrong anyways. There, 'unsigned long' is 32 bits, but pid_t is 64 bits, so we'd be losing information in our hash. We probably need to fix this code to be passing (void *)&pid_t and dereferencing the pointer to get to a full pid, rather than cheating with (void*)(unsigned long)pid_t and possibly losing bits (although since this is in a context of hashing, lost bits only means more chance for collision, and not a fatal algorithmic flaw).
where existing calls to virRandom(256) will now be virRandomBits(8), virRandom(1024*1024*1024) will now be virRandomBits(30), and your code would use uint32_t seed = virRandom(32).
Of course, here I meant virRandomBits(32),
Yep, I've done that.
but I'm sure you figured that out.
+ + return le32toh(r);
<endian.h>, and thus le32toh(), is not yet standardized (although POSIX will be adding it in the future), nor is it currently provided by gnulib. We'd have to get that fixed first.
The le32toh call was only here because the code I copied wanted to be endian neutral. I don't think libvirt really cares if its hash codes are endian neutral, so I trivially just removed the le32toh call and avoid the problem of endian.h
Agreed - we aren't sharing hash values over the wire, so all hash values within a particular libvirtd process will be the same endianness, without having to waste time on swapping bytes around. -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org