On Wed, 2009-07-22 at 15:55 -0400, Mike Waychison wrote:
> > +#define FLEX_ARRAY_INIT(size, total) {{{\
> > + .element_size = (size), \
> > + .nr_elements = 0, \
> > +}}}
> > +
>
> It's not clear how this guy is used. It will initialize a flex_array,
> but how is somebody expected to free the parts that get associated with it?
I tried to make that a bit more clear with the kerneldocs.
flex_array_free_parts() will free just the "parts" without touching the
"base" structure. Otherwise, this macro is used in the same way as
RADIX_TREE_INIT().
> Is there a fancy way to make declaring a flex_array on stack a
> compile-time error?
Not that I know of. One thing that I did which makes this a _bit_
easier to detect is that sizeof(struct flex_array)==PAGE_SIZE instead of
just leaving a "void members[0]" at the end of the struct. That means
that scripts/checkstack.pl should spot these.
I just double-checked:
$ objdump -d ../mhp-build/i386-qemu-smp/vmlinux | scripts/checkstack.pl i386
0xc02499d8 min_free_kbytes_sysctl_handler [vmlinux]: 4096
0xc0276619 do_sys_poll [vmlinux]: 896
0xc0276b49 do_select [vmlinux]: 704
...
That's after I added a 'struct flex_array f;' in
min_free_kbytes_sysctl_handler().
I'm happy to hear of anybody else's tricks, though. I guess I could do
a WARN_ONCE() in some of the flex_array*() functions if we detect an
address that looks to be on the stack. But, I can't think of any fancy
compile-time ones.
-- Dave
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