Re: [PATCH] pc-bios/s390-ccw: Get rid of the the __u* types

[Thomas Huth <thuth@redhat.com>]

On 27/06/2023 14.19, Christian Borntraeger wrote:
> 
> 
> Am 27.06.23 um 13:41 schrieb Thomas Huth:
>> Using types starting with double underscores should be avoided since these
>> names are marked as reserved by the C standard. The corresponding Linux
> 
> In general I think this change is fine, but this is kind of interesting, as
> /usr/include/linux/types.h does have __u64 and friends. In fact there is
> __u64 but not u64 in /usr/include.
> 
> And yes a google search for double underscore  has
> 
> The use of two underscores (` __ ') in identifiers is reserved for the
> compiler's internal use according to the ANSI-C standard. Underscores
> (` _ ') are often used in names of library functions (such as " _main
> " and " _exit "). In order to avoid collisions, do not begin an
> identifier with an underscore.
> 
>> kernel header file has also been changed accordingly a long time ago:
>>
>>   
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/drivers/s390/cio/cio.h?id=cd6b4f27b9bb2a
> 
> but IIRC from a kernel perspective u64 is for kernel internal uint64_t
> and __u64 is for uapi, e.g. see
> https://lkml.indiana.edu/hypermail/linux/kernel/1401.2/02851.html
> 
> So in essence we (QEMU/s390-ccw) have to decide what to use for our
> internal purposes. And yes, u64 and this patch is certainly ok. But
> we might need to change the patch description

Ok, agreed, the patch description could be better. Maybe just something like 
this:

"
The types starting with double underscores have likely been introduced into 
the s390-ccw bios to be able to re-use structs from the Linux kernel in the 
past, but the corresponding structs in cio.h have been changed there a long 
time ago already to not use the variants with the double underscores anymore:

 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/drivers/s390/cio/cio.h?id=cd6b4f27b9bb2a

So it would be good to replace these in the s390-ccw bios now, too.
"

?

  Thomas