kernel/linux.git/include/linux/container_of.h, branch v7.3-rc1

container_of: remove local __mptr variable

2026-07-15T05:15:26+00:00

container_of() can be called in a nested manner to retrieve the grand parent structure as illustrated below: struct foo { int a; }; struct bar { struct foo foo; }; #define to_foo(a_ptr) container_of(a_ptr, struct foo, a) #define to_bar(a_ptr) container_of(to_foo(a_ptr), struct bar, foo) The issue is that the above construct will cause __mptr, the local variable of container_of(), to shadow itself because of the nested call. This then triggers a warning in sparse and W=2 builds. While this warning is benign, it still causes some overhead as proven by below list of commits in which people made local workarounds: - commit 7eab14de73a8 ("mdio, phy: fix -Wshadow warnings triggered by nested container_of()") - commit 8d8c3131248d ("clk: define to_clk_regmap() as inline function") - commit bfb972c5e1cb ("IB/verbs: avoid nested container_of()") - commit 093adbcedf12 ("btrfs: switch helper macros to static inlines in sysfs.h") - commit c1d35dfa0f7d ("rt2x00: Fix sparse warning on nested container_of()") (the list is probably not exhaustive). As a matter of fact, the local variable __mptr is only used once in container_of(). As such, it is not strictly needed. Inline that local __mptr variable to remove once and for all the risk of variable shadowing when nesting container_of() and prevent people from writing further local fixes. Signed-off-by: Vincent Mailhol Link: https://patch.msgid.link/20260714-containerof_refactor-v1-3-b5c31164d2ad@kernel.org Signed-off-by: Greg Kroah-Hartman

container_of: remove useless pair of parentheses

2026-07-15T05:15:26+00:00

The last expression in container_of() doesn't need an extra pair of parenthesis. Remove it. Signed-off-by: Vincent Mailhol Link: https://patch.msgid.link/20260714-containerof_refactor-v1-2-b5c31164d2ad@kernel.org Signed-off-by: Greg Kroah-Hartman

container_of: apply typeof_member() to container_of()

2026-07-15T05:15:26+00:00

container_of() uses the construct below: ((type *)0)->member to retrieve the type of the structure's member and then ensure that it matches the type of the given pointer. This construct being rather difficult to understand, the typeof_member() macro was created to encapsulate it and give it a descriptive name. Apply typeof_member() to container_of() to make it easier to read and understand what this macro does. Signed-off-by: Vincent Mailhol Link: https://patch.msgid.link/20260714-containerof_refactor-v1-1-b5c31164d2ad@kernel.org Signed-off-by: Greg Kroah-Hartman

container_of: Document container_of() is not to be used in new code

2025-07-16T11:56:23+00:00

There is a warning in the kerneldoc documentation of container_of() that constness of its ptr argument is lost. While this is a valid suggestion container_of_const() should be used instead, the vast majority of new code still uses container_of(): $ git diff v6.13 v6.14|grep container_of\(|wc -l 646 $ git diff v6.13 v6.14|grep container_of_const|wc -l 9 Make an explicit recommendation to use container_of_const(). Signed-off-by: Sakari Ailus Link: https://lore.kernel.org/r/20250520103437.468691-1-sakari.ailus@linux.intel.com Signed-off-by: Greg Kroah-Hartman

container_of: Update header inclusions

2023-01-31T11:44:20+00:00

The commit 848dba781f19 ("container_of: remove container_of_safe()") removed the code that uses err.h. Replace the inclusion by stddef.h which provides offsetof() definition which is still in use. Signed-off-by: Andy Shevchenko Link: https://lore.kernel.org/r/20230130111746.59830-1-andriy.shevchenko@linux.intel.com Signed-off-by: Greg Kroah-Hartman

container_of: add container_of_const() that preserves const-ness of the pointer

2022-12-06T15:55:18+00:00

container_of does not preserve the const-ness of a pointer that is passed into it, which can cause C code that passes in a const pointer to get a pointer back that is not const and then scribble all over the data in it. To prevent this, container_of_const() will preserve the const status of the pointer passed into it using the newly available _Generic() method. Suggested-by: Jason Gunthorpe Suggested-by: Sakari Ailus Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: Jason Gunthorpe Reviewed-by: Andy Shevchenko Reviewed-by: Sakari Ailus Acked-by: Rafael J. Wysocki Link: https://lore.kernel.org/r/20221205121206.166576-1-gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman

linux/container_of.h: Warn about loss of constness

2022-10-25T08:28:15+00:00

container_of() casts the original type to another which leads to the loss of the const qualifier if it is not specified in the caller-provided type. This easily leads to container_of() returning a non-const pointer to a const struct which the C compiler does not warn about. Acked-by: Andy Shevchenko Signed-off-by: Sakari Ailus Link: https://lore.kernel.org/r/20221024111627.75183-1-sakari.ailus@linux.intel.com Signed-off-by: Greg Kroah-Hartman

container_of: remove container_of_safe()

2022-10-25T08:27:54+00:00

It came in from a staging driver that has been long removed from the tree, and there are no in-kernel users of the macro, and it's very dubious if anyone should ever use this thing, so just remove it entirely. Reviewed-by: Sakari Ailus Acked-by: Rafael J. Wysocki Acked-by: Andy Shevchenko Link: https://lore.kernel.org/r/20221024123933.3331116-1-gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman

linux/container_of.h: switch to static_assert

2021-11-09T18:02:49+00:00

_Static_assert() is evaluated already in the compiler's frontend, and gives a somehat more to-the-point error, compared to the BUILD_BUG_ON macro, which only fires after the optimizer has had a chance to eliminate calls to functions marked with __attribute__((error)). In theory, this might make builds a tiny bit faster. There's also a little less gunk in the error message emitted: lib/sort.c: In function `foo': include/linux/build_bug.h:78:41: error: static assertion failed: "pointer type mismatch in container_of()" 78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg) compared to lib/sort.c: In function `foo': include/linux/compiler_types.h:322:38: error: call to `__compiletime_assert_2' declared with attribute error: pointer type mismatch in container_of() 322 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) While at it, fix the copy-pasto in container_of_safe(). Link: https://lkml.kernel.org/r/20211015090530.2774079-1-linux@rasmusvillemoes.dk Link: https://lore.kernel.org/lkml/20211014132331.GA4811@kernel.org/T/ Signed-off-by: Rasmus Villemoes Reviewed-by: Miguel Ojeda Acked-by: Andy Shevchenko Reviewed-by: Nick Desaulniers Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kernel.h: split out container_of() and typeof_member() macros

2021-11-09T18:02:49+00:00

kernel.h is being used as a dump for all kinds of stuff for a long time. Here is the attempt cleaning it up by splitting out container_of() and typeof_member() macros. For time being include new header back to kernel.h to avoid twisted indirected includes for existing users. Note, there are _a lot_ of headers and modules that include kernel.h solely for one of these macros and this allows to unburden compiler for the twisted inclusion paths and to make new code cleaner in the future. Link: https://lkml.kernel.org/r/20211013170417.87909-3-andriy.shevchenko@linux.intel.com Signed-off-by: Andy Shevchenko Cc: Boqun Feng Cc: Brendan Higgins Cc: Ingo Molnar Cc: Jonathan Cameron Cc: Laurent Pinchart Cc: Mauro Carvalho Chehab Cc: Miguel Ojeda Cc: Peter Zijlstra Cc: Rasmus Villemoes Cc: Sakari Ailus Cc: Thomas Gleixner Cc: Thorsten Leemhuis Cc: Waiman Long Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds