On Sunday 14 October 2007, Adrian Bunk wrote:
> drivers/net/wireless/rt2x00/rt2x00ring.h contains the following:
>
> <-- snip -->
>
> ...
> /*
> * data_desc
> * Each data entry also contains a descriptor which is used by the
> * device to determine what should be done with the packet and
> * what the current status is.
> * This structure is greatly simplified, but the descriptors
> * are basically a list of little endian 32 bit values.
> * Make the array by default 1 word big, this will allow us
> * to use sizeof() correctly.
> */
> struct data_desc {
> __le32 word[1];
> };
> ...
> /*
> * TX/RX Descriptor access functions.
> */
> static inline void rt2x00_desc_read(struct data_desc *desc,
> const u8 word, u32 *value)
> {
> *value = le32_to_cpu(desc->word[word]);
> }
>
> static inline void rt2x00_desc_write(struct data_desc *desc,
> const u8 word, const u32 value)
> {
> desc->word[word] = cpu_to_le32(value);
> }
> ...
>
> <-- snip -->
>
> I haven't checked whether it might work in all cases, but passing
> non-zero values as second parameter to rt2x00_desc_{read,write}()
> (as is done in many cases) is even in the best case bad coding style.
Access to the array is correct, even with non-zero values the code that is
reading/writing to the array knows the exact size of the descriptor. Within
rt2x00 are however 5 drivers who have different descriptor sizes. That means
I can't create a structure which has the correct array length.
The structure itself is just a simple map over preallocated memory
(skb->data in case of USB or dma in case of PCI).
So possible solutions would be:
- remove struct data_desc and make it a void* or __le32*
This is at the cost of code readibility since the above pointers
have less meaning then a pointer to a structure which can be nicely
documented.
- increase the word[] array to something that fits all (+/- 20 entries)
This wouldn't really be a problem, all it requires is fixing the sizeof()
statements. But then the code should contain a big note about that it
is not allowed to read/write _all_ words in the entry since it depends on
the driver that uses it.
What would in this case be the best solution for good coding style?
Ivo
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