Re: [PATCH 1/1] fs/qnx6: Fix building with GCC 15

[Al Viro <viro@zeniv.linux.org.uk>]

On Sun, Oct 06, 2024 at 07:38:07PM +0000, David Laight wrote:
> ...
> > would explain what was really going on - the point is not to make gcc STFU, it's
> > to make the code more straightforward.  The warning is basically "it smells
> > somewhat fishy around >here<, might be worth taking a look".  And yes, it turned
> > out to be fishy; minimal "make it STFU" would be to strip those NULs from
> > the initializers (i.e. just go for static char match_root[2][3] = {".", ".."}; -
> > an array initializer is zero-padded if it's shorter than the array), but that
> > wasn't the only, er, oddity in that code.
> 
> Indeed - looks like it is checking that the first two directory entries
> are "." and ".." in about the most complex way possible.
> 
> I have vague recollections on some code that ignored the first two entries
> because they 'must be "." and ".."' - and then failed because some filesystem
> (and I can't even remember the O/S) didn't meet its expectations!
> 
> A simple:
> 	if (strcmp(dir_entry[0].de_fname, ".") || strcmp(dir_entry[1].de_fname, ".."))
> 		error = 1;
> would suffice.

memcmp(), please.  strcmp() is _not_ guaranteed to be safe without both being
NUL-terminated; yes, compiler will almost simplify that in case when one of
the arguments is a string literal, but it's better to do straight memcmp() in
this case.  It's not worth trying to be fancy there...