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hash: add comment about multiple values

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This commit is contained in:
David Teigland 2015-11-16 11:01:53 -06:00
parent b6a45963e3
commit 920a281994
1 changed files with 46 additions and 0 deletions
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46
libdm/libdevmapper.h
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@ -1849,6 +1849,52 @@ void *dm_hash_get_data(struct dm_hash_table *t, struct dm_hash_node *n);
struct dm_hash_node *dm_hash_get_first(struct dm_hash_table *t);
struct dm_hash_node *dm_hash_get_next(struct dm_hash_table *t, struct dm_hash_node *n);
/*
* dm_hash_insert() replaces the value of an existing
* entry with a matching key if one exists. Otherwise
* it adds a new entry.
*
* dm_hash_insert_withval() inserts a new entry if
* another entry with the same key already exists.
* val_len is the size of the data being inserted.
*
* If two entries with the same key exist,
* (added using dm_hash_insert_multival), then:
* . dm_hash_lookup() returns the first one it finds, and
* dm_hash_lookup_withval() returns the one with a matching
* val_len/val.
* . dm_hash_remove() removes the first one it finds, and
* dm_hash_remove_withval() removes the one with a matching
* val_len/val.
*
* If a single entry with a given key exists, and it has
* zero val_len, then:
* . dm_hash_lookup() returns it
* . dm_hash_lookup_withval(val_len=0) returns it
* . dm_hash_remove() removes it
* . dm_hash_remove_withval(val_len=0) removes it
*
* dm_hash_lookup_multival() is a single call that will
* both lookup a key's value and check if there is more
* than one entry with the given key.
*
* (It is not meant to retrieve all the entries with the
* given key. In the common case where a single entry exists
* for the key, it is useful to have a single call that will
* both look up the value and indicate if multiple values
* exist for the key.)
*
* dm_hash_lookup_multival:
* . If no entries exist, the function returns NULL, and
* the val2 arg is set to NULL.
* . If only one entry exists, the value of that entry is
* returned and the val2 arg is set to NULL.
* . If more than one entry exists, the value of one entry
* is returned and the val2 arg is set to the value of a
* second entry. Testing that the val2 arg is not NULL
* indicates that more than one entry exists.
*/
void *dm_hash_lookup_withval(struct dm_hash_table *t, const char *key,
const void *val, uint32_t val_len);
void dm_hash_remove_withval(struct dm_hash_table *t, const char *key,