On Sat, May 03, 2014 at 09:01:01AM +0900, YAMAMOTO Takashi wrote:
> xmalloc_cacheline API is relatively new. It's better
> not to inherit the kludge from xmalloc. This kind of
> kludge rather hurts these days.
>
> Signed-off-by: YAMAMOTO Takashi <yamam...@valinux.co.jp>
I see basically three alternatives for xmalloc(0) and
xmalloc_cacheline(0):
1. Assert-fail.
2. Return NULL.
3. Return a unique 1-byte block.
I'm not a big fan of #1 because it can create corner cases where one
must be extra careful, mainly when one is allocating a variable-length
array that might occasionally have zero elements.
#2 and #3 have about the same effect most of the time. Since
dereferencing the pointer returned by #3 yields undefined behavior
according to the C standard, there isn't much of an advantage to #3 over
#2. The only practical difference is that occasionally a nonnull
pointer indicates that some data structure has been initialized.
I've always leaned toward #2, as a personal opinion, but I went with #3
in Open vSwitch xmalloc() because of my GNU background, since GNU code
has a bias toward malloc(0) acting like malloc(1). (gnulib goes so far
as to test for malloc(0) behavior and add a wrapper if it returns NULL.)
So my preference is #2 or #3, leaning toward #3 since it's the behavior
we've had in OVS for a long time. To me, #1 seems risky: it makes a
rare corner case definitely deadly.
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