Re: staging/wlan-ng query: convert to flexible array member

Deepak R Varma
2022-11-08T15:45:22Z

On Tue, Nov 08, 2022 at 04:34:15PM +0100, Greg Kroah-Hartman wrote:
> On Tue, Nov 08, 2022 at 08:42:59PM +0530, Deepak R Varma wrote:
> > Hello,
> >
> > First, my apologies for the long email.
> > I am requesting guidance on how to approach resolving the zero element flexible
> > VLO struct implementation in this driver in file drivers/staging/waln-ng/hfa384x.f
> >
> > The struct hfa384x_pdrec contains nested structs with zero element arrays. These
> > zero element structs are part of a union 'data' inside the struct container. This
> > union 'data' is the last element of this container. Please see the code snip below:
> >
> > <snip>
> >
> > 1068 struct hfa384x_pdrec {
> > 1 __le16 len; /* in words */
> > 2 __le16 code;
> > 3 union pdr {
> > 4 struct hfa384x_pdr_pcb_partnum pcb_partnum;
> > 11 struct hfa384x_pdr_nicid nicid;
> > 12 struct hfa384x_pdr_refdac_measurements refdac_measurements;
> > 13 struct hfa384x_pdr_vgdac_measurements vgdac_measurements;
> > 14 struct hfa384x_pdr_level_comp_measurements level_compc_measurements;
> > 15 struct hfa384x_pdr_mac_address mac_address;
> > 39 } data;
> > 40 } __packed;
> >
> > </snip>
> >
> > The three structures in question are declared as follows in the same file:
> >
> > <snip>
> > 962 struct hfa384x_pdr_refdac_measurements {
> > 1 u16 value[0];
> > 2 } __packed;
> > 3
> > 4 struct hfa384x_pdr_vgdac_measurements {
> > 5 u16 value[0];
> > 6 } __packed;
> > 7
> > 8 struct hfa384x_pdr_level_comp_measurements {
> > 9 u16 value[0];
> > 10 } __packed;
> > </snip>
> >
> > As per the C99 specifications, the flexible array struct should have at least
> > one member other than the true flexible array member. So converting these from
> > [0] to [] is not feasible in the current form.
> >
> > I did not find these struct variables being used for memory allocation in the
> > code directly. My find may be short since the implementation appears to get very
> > complex as I tried to get deeper.
> >
> > Can you please suggest how should I approach correcting the zero element flex
> > array implementation here? Can these structs be removed if they are unused?
>
> Are you sure they are unused?
>
> They look like structures that are read from the memory of a device,
> right? Try removing the structures from the union and see what happens
> :)

I did remove the structs from the union and it built fine. Is there anything else I
can check/test to verify the impact?

<snip>
drv@qemulion:~/git/kernels/staging$ git diff
diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
index 0611e37df6ac..8fe10aa93dfb 100644
--- a/drivers/staging/wlan-ng/hfa384x.h
+++ b/drivers/staging/wlan-ng/hfa384x.h
@@ -1077,9 +1077,6 @@ struct hfa384x_pdrec {
struct hfa384x_pdr_mfisuprange mfisuprange;
struct hfa384x_pdr_cfisuprange cfisuprange;
struct hfa384x_pdr_nicid nicid;
- struct hfa384x_pdr_refdac_measurements refdac_measurements;
- struct hfa384x_pdr_vgdac_measurements vgdac_measurements;
- struct hfa384x_pdr_level_comp_measurements level_compc_measurements;
struct hfa384x_pdr_mac_address mac_address;
struct hfa384x_pdr_mkk_callname mkk_callname;
struct hfa384x_pdr_regdomain regdomain;
drv@qemulion:~/git/kernels/staging$ make M=drivers/staging/wlan-ng/
CC [M] drivers/staging/wlan-ng/prism2usb.o
CC [M] drivers/staging/wlan-ng/p80211netdev.o
LD [M] drivers/staging/wlan-ng/prism2_usb.o
MODPOST drivers/staging/wlan-ng/Module.symvers
LD [M] drivers/staging/wlan-ng/prism2_usb.ko
BTF [M] drivers/staging/wlan-ng/prism2_usb.ko
drv@qemulion:~/git/kernels/staging$
</snip>

>
> thanks,
>
> greg k-h