| Norman James | 6a58a27 | 2015-10-07 14:34:16 -0500 | [diff] [blame] | 1 | /* CC0 (Public domain) - see LICENSE file for details */
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| 2 | #ifndef CCAN_CONTAINER_OF_H
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| 3 | #define CCAN_CONTAINER_OF_H
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| 4 | #include <stddef.h>
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| 5 |
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| 6 | #include "config.h"
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| 7 | #include <ccan/check_type/check_type.h>
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| 8 |
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| 9 | /**
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| 10 | * container_of - get pointer to enclosing structure
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| 11 | * @member_ptr: pointer to the structure member
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| 12 | * @containing_type: the type this member is within
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| 13 | * @member: the name of this member within the structure.
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| 14 | *
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| 15 | * Given a pointer to a member of a structure, this macro does pointer
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| 16 | * subtraction to return the pointer to the enclosing type.
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| 17 | *
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| 18 | * Example:
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| 19 | * struct foo {
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| 20 | * int fielda, fieldb;
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| 21 | * // ...
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| 22 | * };
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| 23 | * struct info {
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| 24 | * int some_other_field;
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| 25 | * struct foo my_foo;
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| 26 | * };
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| 27 | *
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| 28 | * static struct info *foo_to_info(struct foo *foo)
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| 29 | * {
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| 30 | * return container_of(foo, struct info, my_foo);
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| 31 | * }
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| 32 | */
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| 33 | #define container_of(member_ptr, containing_type, member) \
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| 34 | ((containing_type *) \
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| 35 | ((char *)(member_ptr) \
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| 36 | - container_off(containing_type, member)) \
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| 37 | + check_types_match(*(member_ptr), ((containing_type *)0)->member))
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| 38 |
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| 39 | /**
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| 40 | * container_off - get offset to enclosing structure
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| 41 | * @containing_type: the type this member is within
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| 42 | * @member: the name of this member within the structure.
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| 43 | *
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| 44 | * Given a pointer to a member of a structure, this macro does
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| 45 | * typechecking and figures out the offset to the enclosing type.
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| 46 | *
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| 47 | * Example:
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| 48 | * struct foo {
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| 49 | * int fielda, fieldb;
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| 50 | * // ...
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| 51 | * };
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| 52 | * struct info {
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| 53 | * int some_other_field;
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| 54 | * struct foo my_foo;
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| 55 | * };
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| 56 | *
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| 57 | * static struct info *foo_to_info(struct foo *foo)
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| 58 | * {
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| 59 | * size_t off = container_off(struct info, my_foo);
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| 60 | * return (void *)((char *)foo - off);
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| 61 | * }
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| 62 | */
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| 63 | #define container_off(containing_type, member) \
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| 64 | offsetof(containing_type, member)
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| 65 |
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| 66 | /**
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| 67 | * container_of_var - get pointer to enclosing structure using a variable
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| 68 | * @member_ptr: pointer to the structure member
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| 69 | * @container_var: a pointer of same type as this member's container
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| 70 | * @member: the name of this member within the structure.
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| 71 | *
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| 72 | * Given a pointer to a member of a structure, this macro does pointer
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| 73 | * subtraction to return the pointer to the enclosing type.
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| 74 | *
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| 75 | * Example:
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| 76 | * static struct info *foo_to_i(struct foo *foo)
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| 77 | * {
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| 78 | * struct info *i = container_of_var(foo, i, my_foo);
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| 79 | * return i;
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| 80 | * }
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| 81 | */
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| 82 | #if HAVE_TYPEOF
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| 83 | #define container_of_var(member_ptr, container_var, member) \
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| 84 | container_of(member_ptr, typeof(*container_var), member)
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| 85 | #else
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| 86 | #define container_of_var(member_ptr, container_var, member) \
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| 87 | ((void *)((char *)(member_ptr) - \
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| 88 | container_off_var(container_var, member)))
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| 89 | #endif
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| 90 |
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| 91 | /**
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| 92 | * container_off_var - get offset of a field in enclosing structure
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| 93 | * @container_var: a pointer to a container structure
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| 94 | * @member: the name of a member within the structure.
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| 95 | *
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| 96 | * Given (any) pointer to a structure and a its member name, this
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| 97 | * macro does pointer subtraction to return offset of member in a
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| 98 | * structure memory layout.
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| 99 | *
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| 100 | */
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| 101 | #if HAVE_TYPEOF
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| 102 | #define container_off_var(var, member) \
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| 103 | container_off(typeof(*var), member)
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| 104 | #else
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| 105 | #define container_off_var(var, member) \
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| 106 | ((char *)&(var)->member - (char *)(var))
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| 107 | #endif
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| 108 |
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| 109 | #endif /* CCAN_CONTAINER_OF_H */
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