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e7f6d9e25a
* ccan/container_of/container_of.h (container_of_or_null): added [ccan 7ec5b8e06b2fd5fa98b1fcde1158c286d2d429d8] (David Gibson) It's quite common to have a pointer which could be either a pointer to a structure member, or NULL. This needs special casing with container_of(), or it will convert NULL into something strange. This patch adds container_of_or_null(), which will return NULL if passed (an appropriately typed) NULL, or the containining structure as container_of() otherwise. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47579 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
142 lines
4.1 KiB
C
142 lines
4.1 KiB
C
/* CC0 (Public domain) - see ccan/licenses/CC0 file for details */
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#ifndef CCAN_CONTAINER_OF_H
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#define CCAN_CONTAINER_OF_H
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#include "ccan/check_type/check_type.h"
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/**
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* container_of - get pointer to enclosing structure
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* @member_ptr: pointer to the structure member
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* @containing_type: the type this member is within
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* @member: the name of this member within the structure.
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*
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* Given a pointer to a member of a structure, this macro does pointer
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* subtraction to return the pointer to the enclosing type.
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*
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* Example:
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* struct foo {
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* int fielda, fieldb;
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* // ...
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* };
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* struct info {
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* int some_other_field;
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* struct foo my_foo;
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* };
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*
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* static struct info *foo_to_info(struct foo *foo)
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* {
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* return container_of(foo, struct info, my_foo);
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* }
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*/
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#define container_of(member_ptr, containing_type, member) \
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((containing_type *) \
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((char *)(member_ptr) \
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- container_off(containing_type, member)) \
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+ check_types_match(*(member_ptr), ((containing_type *)0)->member))
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/**
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* container_of_or_null - get pointer to enclosing structure, or NULL
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* @member_ptr: pointer to the structure member
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* @containing_type: the type this member is within
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* @member: the name of this member within the structure.
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*
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* Given a pointer to a member of a structure, this macro does pointer
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* subtraction to return the pointer to the enclosing type, unless it
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* is given NULL, in which case it also returns NULL.
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*
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* Example:
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* struct foo {
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* int fielda, fieldb;
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* // ...
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* };
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* struct info {
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* int some_other_field;
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* struct foo my_foo;
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* };
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*
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* static struct info *foo_to_info_allowing_null(struct foo *foo)
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* {
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* return container_of_or_null(foo, struct info, my_foo);
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* }
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*/
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static inline char *container_of_or_null_(void *member_ptr, size_t offset)
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{
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return member_ptr ? (char *)member_ptr - offset : NULL;
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}
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#define container_of_or_null(member_ptr, containing_type, member) \
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((containing_type *) \
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container_of_or_null_(member_ptr, \
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container_off(containing_type, member)) \
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+ check_types_match(*(member_ptr), ((containing_type *)0)->member))
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/**
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* container_off - get offset to enclosing structure
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* @containing_type: the type this member is within
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* @member: the name of this member within the structure.
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*
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* Given a pointer to a member of a structure, this macro does
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* typechecking and figures out the offset to the enclosing type.
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*
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* Example:
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* struct foo {
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* int fielda, fieldb;
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* // ...
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* };
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* struct info {
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* int some_other_field;
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* struct foo my_foo;
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* };
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*
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* static struct info *foo_to_info(struct foo *foo)
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* {
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* size_t off = container_off(struct info, my_foo);
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* return (void *)((char *)foo - off);
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* }
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*/
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#define container_off(containing_type, member) \
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offsetof(containing_type, member)
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/**
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* container_of_var - get pointer to enclosing structure using a variable
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* @member_ptr: pointer to the structure member
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* @container_var: a pointer of same type as this member's container
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* @member: the name of this member within the structure.
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*
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* Given a pointer to a member of a structure, this macro does pointer
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* subtraction to return the pointer to the enclosing type.
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*
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* Example:
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* static struct info *foo_to_i(struct foo *foo)
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* {
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* struct info *i = container_of_var(foo, i, my_foo);
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* return i;
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* }
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*/
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#if HAVE_TYPEOF
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#define container_of_var(member_ptr, container_var, member) \
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container_of(member_ptr, typeof(*container_var), member)
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#else
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#define container_of_var(member_ptr, container_var, member) \
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((void *)((char *)(member_ptr) - \
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container_off_var(container_var, member)))
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#endif
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/**
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* container_off_var - get offset of a field in enclosing structure
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* @container_var: a pointer to a container structure
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* @member: the name of a member within the structure.
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*
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* Given (any) pointer to a structure and a its member name, this
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* macro does pointer subtraction to return offset of member in a
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* structure memory layout.
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*
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*/
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#if HAVE_TYPEOF
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#define container_off_var(var, member) \
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container_off(typeof(*var), member)
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#else
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#define container_off_var(var, member) \
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((const char *)&(var)->member - (const char *)(var))
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#endif
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#endif /* CCAN_CONTAINER_OF_H */
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