On Sun, Jun 27, 2021 at 04:23:26PM +0100, Matthew Wilcox wrote:

On Sun, Jun 27, 2021 at 12:53:47PM +0200, Greg KH wrote:

quoted

quoted

+enum ops { DIGEST_LIST_ADD, DIGEST_LIST_DEL, DIGEST_LIST_OP__LAST };
+

For enums you export to userspace, you need to specify the values so
that all compilers get them right.

I've never heard that rule before.  Where does it come from?
https://en.cppreference.com/w/c/language/enum
says:

  If enumeration-constant is not followed by = constant-expression,
  its value is the value one greater than the value of the previous
  enumerator in the same enumeration. The value of the first enumerator
  (if it does not use = constant-expression) is zero.

I thought it was in the Documentation/driver-api/ioctl.rst file, but I
can't find it right now.  Maybe it was something that Arnd said?

Arnd, is this still an issue?  For some reason I thought it was always
good to have uapi .h enums be explicit as to the value in them,
otherwise some C compilers might produce other values if they were not
specified?

thanks,

greg k-h