On Tue, 2023-09-12 at 18:00 -0500, Benjamin Marzinski wrote:
> On Mon, Sep 11, 2023 at 06:38:31PM +0200, mwilck@xxxxxxxx wrote:
> > From: Martin Wilck <mwilck@xxxxxxxx>
> >
> > The current sort order of aliases is alphabetical, which is does
> > not match
> > the actual order of aliases, where "mpathaa" > "mpathz". Change the
> > ordering as
> > follows: first sort by string length, then alphabetically. This
> > will make
> > sure that for aliases with the same prefix, alias order is correct
> > ("mpathaaa"
> > will be sorted after "mpathzz", etc). Even for mixed prefixes, the
> > alias
> > order will be correct for every individual prefix, even though
> > aliases with
> > different prefixes may alternate in the file.
> >
> > Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> > ---
> > libmultipath/alias.c | 45 +++++++++++++++++++++++++++++++++-------
> > ----
> > 1 file changed, 34 insertions(+), 11 deletions(-)
> >
> > diff --git a/libmultipath/alias.c b/libmultipath/alias.c
> > index 58436ec..af6565b 100644
> > --- a/libmultipath/alias.c
> > +++ b/libmultipath/alias.c
> > @@ -117,6 +117,35 @@ static const struct binding
> > *get_binding_for_wwid(const Bindings *bindings,
> > return NULL;
> > }
> >
> > +/*
> > + * Sort order for aliases.
> > + *
> > + * The "numeric" ordering of aliases for a given prefix P is
> > + * Pa, ..., Pz, Paa, ..., Paz, Pba, ... , Pzz, Paaa, ..., Pzzz,
> > Paaaa, ...
> > + * We use the fact that for equal prefix, longer strings are
> > always
> > + * higher than shorter ones. Strings of equal length are sorted
> > alphabetically.
> > + * This is achieved by sorting be length first, then using
> > strcmp().
> > + * If multiple prefixes are in use, the aliases with a given
> > prefix will
> > + * not necessarily be in a contiguous range of the vector, but
> > they will
> > + * be ordered such that for a given prefix, numercally higher
> > aliases will
> > + * always be sorted after lower ones.
> > + */
> > +static int alias_compar(const void *p1, const void *p2)
> > +{
>
> I'm confused as to why we need to pass p1 and p2 and pointers to
> pointers to chars, instead of simply as pointers to chars. We always
> derefence them immediately, and only use the dereferenced pointers.
> Am I
> missing something?
I wanted to make the relationship of alias_compar() and
mp_alias_compar() as obvious as possible. mp_alias_compar() takes
(struct mpentry **) arguments, because it's used as an argument to
vector_sort() aka msort(), which has the same calling convention as
qsort()'s "compar" argument. Therefore I wrote alias_compar() such that
it takes (char **) pointers. This way we could use alias_compar() as an
argument to vector_sort() as well, even though we currently don't.
Does this make sense? If not, I can change it, but I think the function
should not be named alias_compar() if it can't be passed to
vector_sort().
Martin
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