Hi Mauro,
> As commented, don't use WARN_ON(). At most, you could use WARN_ON_ONCE(),
> as otherwise, you may end by causing serious performance issues if
> the code starts to produce a flood of warnings at the dmesg.
>
> I would use pr_warn_ratelimit() on all such cases.
>
OK.
> I don't like the idea of changing the "from" buffer endiannes, copy
> and then restore it back to the original state. Is this really needed?
>
> I would, instead, define:
>
> struct pes_header {
> ...
> __be32 bitfield;
> __be16 length;
> ...
> };
>
> Then wherever you would touch them:
>
> u32 bitfield;
> u16 len;
>
> /* Write into BE fields */
> pes_header.bitfield = cpu_to_be32(bitfield);
> pes_header.length = cpu_to_be16(len);
>
> /* Read from BE fields */
> bitfield = be32_to_cpu(pes_header.bitfield);
> len = be16_to_cpu(pes_header.length);
>
>
> As a side effect, when you use "__be16" and "__be32" types, gcc
> and smatch/sparse will warn you if you mess with endiannes.
>
> Same applies to similar code elsewhere.
>
I don't like it either, it is error prone. I did not know about this
other possibility. Does this work for _bitfields_ though?
I think the authors for libdvbv5 used unions precisely so bswap() could
be called on a 'bitfield' member and from then on the bitfields could be
accessed directly, e.g.:
union {
u16 bitfield; <-- call bswap() on this
struct {
--> then use these directly:
u8 syntax:1;
u8 zero:1;
u8 one:2;
u16 section_length:12;
} __packed;
} __packed
At least that's what I understood.
I found this:
https://lwn.net/Articles/741762/
Maybe *_get_bits, *_replace_bits is the equivalent that I should use for bitfields?
Because I'd rather not do this:
> u32 bitfield;
> /* Write into BE fields */
> pes_header.bitfield = cpu_to_be32(bitfield);
Since I'd have to write the (many!) bitwise operations myself and I'm
sure I will mess this up at _some_ point.
thanks,
- Daniel
