Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH 1/1] linux/container_of.h: Warn about loss of constness | Date | Mon, 24 Oct 2022 09:46:40 +0000 |
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From: 'Andy Shevchenko' > Sent: 24 October 2022 10:37 > ... > > > > > > Wait, no one uses this macro, so why not just remove it entirely? > > > > > > > > Good question. It appears to be a (relatively) common pattern to look up > > > > something and the return its containing object if the lookup was > > > > successful. Doing a quick > > > > > > > > $ git grep 'container_of.*:' drivers include > > > > > > > > reveals more than 20 instances of the pattern. There are probably more > > > > those that use if for testing for NULL. I guess people don't know about > > > > this macro, apart from the developers of the staging driver it was added > > > > for (commit 05e6557b8ed833546ee2b66ce6b58fecf09f439e). > > > > > > Maybe we can provide an example to keep this macro in the kernel, meaning > > > convert one of the drivers / subsystem to actually use it? > > > > Adding _safe() to a function name doesn't actually tell you anything. > > You still need to look up what it is 'safe' against. > > > > In this case the full code pattern is actually much clearer. > > > > It is also quite likely that it is followed by an: > > if (!ptr) > > return xxx; > > You that can/should really be put before the container_of() call. > > return statements in macros are no go. Or you meant something else?
I meant in the function itself.
It might be interesting to check how many of the function can actually have a NULL pointer? Especially in staging code might be being 'defensive'.
David
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