On Wed, Aug 26, 2020 at 12:55:28PM +0300, Dan Carpenter wrote:

On Wed, Aug 26, 2020 at 07:21:35AM +0530, Allen Pais wrote:

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On Thu, Aug 20, 2020 at 3:09 AM James Bottomley
[off-list ref] wrote:

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On Wed, 2020-08-19 at 21:54 +0530, Allen wrote:

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[...]

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Since both threads seem to have petered out, let me suggest in
kernel.h:

#define cast_out(ptr, container, member) \
    container_of(ptr, typeof(*container), member)

It does what you want, the argument order is the same as
container_of with the only difference being you name the
containing structure instead of having to specify its type.

Not to incessantly bike shed on the naming, but I don't like
cast_out, it's not very descriptive. And it has connotations of
getting rid of something, which isn't really true.

Um, I thought it was exactly descriptive: you're casting to the
outer container.  I thought about following the C++ dynamic casting
style, so out_cast(), but that seemed a bit pejorative.  What about
outer_cast()?

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FWIW, I like the from_ part of the original naming, as it has
some clues as to what is being done here. Why not just
from_container()? That should immediately tell people what it
does without having to look up the implementation, even before
this becomes a part of the accepted coding norm.

I'm not opposed to container_from() but it seems a little less
descriptive than outer_cast() but I don't really care.  I always
have to look up container_of() when I'm using it so this would just
be another macro of that type ...

 So far we have a few which have been suggested as replacement
for from_tasklet()

- out_cast() or outer_cast()
- from_member().
- container_from() or from_container()

from_container() sounds fine, would trimming it a bit work? like
from_cont().

I'm fine with container_from().  It's the same form as container_of()
and I think we need urgent agreement to not stall everything else so
the most innocuous name is likely to get the widest acceptance.

Kees,

  Will you be  sending the newly proposed API to Linus? I have V2
which uses container_from()
ready to be sent out.

I liked that James swapped the first two arguments so that it matches
container_of().  Plus it's nice that when you have:

	struct whatever *foo = container_from(ptr, foo, member);

Then it means that "ptr == &foo->member".

I'm a bit stalled right now -- the merge window was keeping me busy, and
this week is the Linux Plumbers Conference. This is on my list, but I
haven't gotten back around to it. If you want, feel free to send the
container_from() patch; you might be able to unblock this faster than me
right now. :)

-Kees

-- 
Kees Cook