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diff --git a/secure/lib/libcrypto/man/lhash.3 b/secure/lib/libcrypto/man/lhash.3 new file mode 100644 index 0000000..789e40d --- /dev/null +++ b/secure/lib/libcrypto/man/lhash.3 @@ -0,0 +1,430 @@ +.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.28) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" Set up some character translations and predefined strings. \*(-- will +.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left +.\" double quote, and \*(R" will give a right double quote. \*(C+ will +.\" give a nicer C++. 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Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH "NAME" +lh_new, lh_free, lh_insert, lh_delete, lh_retrieve, lh_doall, lh_doall_arg, lh_error \- dynamic hash table +.SH "SYNOPSIS" +.IX Header "SYNOPSIS" +.Vb 1 +\& #include <openssl/lhash.h> +\& +\& DECLARE_LHASH_OF(<type>); +\& +\& LHASH *lh_<type>_new(); +\& void lh_<type>_free(LHASH_OF(<type> *table); +\& +\& <type> *lh_<type>_insert(LHASH_OF(<type> *table, <type> *data); +\& <type> *lh_<type>_delete(LHASH_OF(<type> *table, <type> *data); +\& <type> *lh_retrieve(LHASH_OF<type> *table, <type> *data); +\& +\& void lh_<type>_doall(LHASH_OF(<type> *table, LHASH_DOALL_FN_TYPE func); +\& void lh_<type>_doall_arg(LHASH_OF(<type> *table, LHASH_DOALL_ARG_FN_TYPE func, +\& <type2>, <type2> *arg); +\& +\& int lh_<type>_error(LHASH_OF(<type> *table); +\& +\& typedef int (*LHASH_COMP_FN_TYPE)(const void *, const void *); +\& typedef unsigned long (*LHASH_HASH_FN_TYPE)(const void *); +\& typedef void (*LHASH_DOALL_FN_TYPE)(const void *); +\& typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *); +.Ve +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +This library implements type-checked dynamic hash tables. The hash +table entries can be arbitrary structures. Usually they consist of key +and value fields. +.PP +lh_<type>\fI_new()\fR creates a new \fB\s-1LHASH_OF\s0(<type\fR> structure to store +arbitrary data entries, and provides the 'hash' and 'compare' +callbacks to be used in organising the table's entries. The \fBhash\fR +callback takes a pointer to a table entry as its argument and returns +an unsigned long hash value for its key field. The hash value is +normally truncated to a power of 2, so make sure that your hash +function returns well mixed low order bits. The \fBcompare\fR callback +takes two arguments (pointers to two hash table entries), and returns +0 if their keys are equal, non-zero otherwise. If your hash table +will contain items of some particular type and the \fBhash\fR and +\&\fBcompare\fR callbacks hash/compare these types, then the +\&\fB\s-1DECLARE_LHASH_HASH_FN\s0\fR and \fB\s-1IMPLEMENT_LHASH_COMP_FN\s0\fR macros can be +used to create callback wrappers of the prototypes required by +lh_<type>\fI_new()\fR. These provide per-variable casts before calling the +type-specific callbacks written by the application author. These +macros, as well as those used for the \*(L"doall\*(R" callbacks, are defined +as; +.PP +.Vb 7 +\& #define DECLARE_LHASH_HASH_FN(name, o_type) \e +\& unsigned long name##_LHASH_HASH(const void *); +\& #define IMPLEMENT_LHASH_HASH_FN(name, o_type) \e +\& unsigned long name##_LHASH_HASH(const void *arg) { \e +\& const o_type *a = arg; \e +\& return name##_hash(a); } +\& #define LHASH_HASH_FN(name) name##_LHASH_HASH +\& +\& #define DECLARE_LHASH_COMP_FN(name, o_type) \e +\& int name##_LHASH_COMP(const void *, const void *); +\& #define IMPLEMENT_LHASH_COMP_FN(name, o_type) \e +\& int name##_LHASH_COMP(const void *arg1, const void *arg2) { \e +\& const o_type *a = arg1; \e +\& const o_type *b = arg2; \e +\& return name##_cmp(a,b); } +\& #define LHASH_COMP_FN(name) name##_LHASH_COMP +\& +\& #define DECLARE_LHASH_DOALL_FN(name, o_type) \e +\& void name##_LHASH_DOALL(void *); +\& #define IMPLEMENT_LHASH_DOALL_FN(name, o_type) \e +\& void name##_LHASH_DOALL(void *arg) { \e +\& o_type *a = arg; \e +\& name##_doall(a); } +\& #define LHASH_DOALL_FN(name) name##_LHASH_DOALL +\& +\& #define DECLARE_LHASH_DOALL_ARG_FN(name, o_type, a_type) \e +\& void name##_LHASH_DOALL_ARG(void *, void *); +\& #define IMPLEMENT_LHASH_DOALL_ARG_FN(name, o_type, a_type) \e +\& void name##_LHASH_DOALL_ARG(void *arg1, void *arg2) { \e +\& o_type *a = arg1; \e +\& a_type *b = arg2; \e +\& name##_doall_arg(a, b); } +\& #define LHASH_DOALL_ARG_FN(name) name##_LHASH_DOALL_ARG +\& +\& An example of a hash table storing (pointers to) structures of type \*(AqSTUFF\*(Aq +\& could be defined as follows; +\& +\& /* Calculates the hash value of \*(Aqtohash\*(Aq (implemented elsewhere) */ +\& unsigned long STUFF_hash(const STUFF *tohash); +\& /* Orders \*(Aqarg1\*(Aq and \*(Aqarg2\*(Aq (implemented elsewhere) */ +\& int stuff_cmp(const STUFF *arg1, const STUFF *arg2); +\& /* Create the type\-safe wrapper functions for use in the LHASH internals */ +\& static IMPLEMENT_LHASH_HASH_FN(stuff, STUFF); +\& static IMPLEMENT_LHASH_COMP_FN(stuff, STUFF); +\& /* ... */ +\& int main(int argc, char *argv[]) { +\& /* Create the new hash table using the hash/compare wrappers */ +\& LHASH_OF(STUFF) *hashtable = lh_STUFF_new(LHASH_HASH_FN(STUFF_hash), +\& LHASH_COMP_FN(STUFF_cmp)); +\& /* ... */ +\& } +.Ve +.PP +lh_<type>\fI_free()\fR frees the \fB\s-1LHASH_OF\s0(<type\fR> structure +\&\fBtable\fR. Allocated hash table entries will not be freed; consider +using lh_<type>\fI_doall()\fR to deallocate any remaining entries in the +hash table (see below). +.PP +lh_<type>\fI_insert()\fR inserts the structure pointed to by \fBdata\fR into +\&\fBtable\fR. If there already is an entry with the same key, the old +value is replaced. Note that lh_<type>\fI_insert()\fR stores pointers, the +data are not copied. +.PP +lh_<type>\fI_delete()\fR deletes an entry from \fBtable\fR. +.PP +lh_<type>\fI_retrieve()\fR looks up an entry in \fBtable\fR. Normally, \fBdata\fR +is a structure with the key field(s) set; the function will return a +pointer to a fully populated structure. +.PP +lh_<type>\fI_doall()\fR will, for every entry in the hash table, call +\&\fBfunc\fR with the data item as its parameter. For lh_<type>\fI_doall()\fR +and lh_<type>\fI_doall_arg()\fR, function pointer casting should be avoided +in the callbacks (see \fB\s-1NOTE\s0\fR) \- instead use the declare/implement +macros to create type-checked wrappers that cast variables prior to +calling your type-specific callbacks. An example of this is +illustrated here where the callback is used to cleanup resources for +items in the hash table prior to the hashtable itself being +deallocated: +.PP +.Vb 9 +\& /* Cleans up resources belonging to \*(Aqa\*(Aq (this is implemented elsewhere) */ +\& void STUFF_cleanup_doall(STUFF *a); +\& /* Implement a prototype\-compatible wrapper for "STUFF_cleanup" */ +\& IMPLEMENT_LHASH_DOALL_FN(STUFF_cleanup, STUFF) +\& /* ... then later in the code ... */ +\& /* So to run "STUFF_cleanup" against all items in a hash table ... */ +\& lh_STUFF_doall(hashtable, LHASH_DOALL_FN(STUFF_cleanup)); +\& /* Then the hash table itself can be deallocated */ +\& lh_STUFF_free(hashtable); +.Ve +.PP +When doing this, be careful if you delete entries from the hash table +in your callbacks: the table may decrease in size, moving the item +that you are currently on down lower in the hash table \- this could +cause some entries to be skipped during the iteration. The second +best solution to this problem is to set hash\->down_load=0 before +you start (which will stop the hash table ever decreasing in size). +The best solution is probably to avoid deleting items from the hash +table inside a \*(L"doall\*(R" callback! +.PP +lh_<type>\fI_doall_arg()\fR is the same as lh_<type>\fI_doall()\fR except that +\&\fBfunc\fR will be called with \fBarg\fR as the second argument and \fBfunc\fR +should be of type \fB\s-1LHASH_DOALL_ARG_FN_TYPE\s0\fR (a callback prototype +that is passed both the table entry and an extra argument). As with +\&\fIlh_doall()\fR, you can instead choose to declare your callback with a +prototype matching the types you are dealing with and use the +declare/implement macros to create compatible wrappers that cast +variables before calling your type-specific callbacks. An example of +this is demonstrated here (printing all hash table entries to a \s-1BIO\s0 +that is provided by the caller): +.PP +.Vb 8 +\& /* Prints item \*(Aqa\*(Aq to \*(Aqoutput_bio\*(Aq (this is implemented elsewhere) */ +\& void STUFF_print_doall_arg(const STUFF *a, BIO *output_bio); +\& /* Implement a prototype\-compatible wrapper for "STUFF_print" */ +\& static IMPLEMENT_LHASH_DOALL_ARG_FN(STUFF, const STUFF, BIO) +\& /* ... then later in the code ... */ +\& /* Print out the entire hashtable to a particular BIO */ +\& lh_STUFF_doall_arg(hashtable, LHASH_DOALL_ARG_FN(STUFF_print), BIO, +\& logging_bio); +.Ve +.PP +lh_<type>\fI_error()\fR can be used to determine if an error occurred in the last +operation. lh_<type>\fI_error()\fR is a macro. +.SH "RETURN VALUES" +.IX Header "RETURN VALUES" +lh_<type>\fI_new()\fR returns \fB\s-1NULL\s0\fR on error, otherwise a pointer to the new +\&\fB\s-1LHASH\s0\fR structure. +.PP +When a hash table entry is replaced, lh_<type>\fI_insert()\fR returns the value +being replaced. \fB\s-1NULL\s0\fR is returned on normal operation and on error. +.PP +lh_<type>\fI_delete()\fR returns the entry being deleted. \fB\s-1NULL\s0\fR is returned if +there is no such value in the hash table. +.PP +lh_<type>\fI_retrieve()\fR returns the hash table entry if it has been found, +\&\fB\s-1NULL\s0\fR otherwise. +.PP +lh_<type>\fI_error()\fR returns 1 if an error occurred in the last operation, 0 +otherwise. +.PP +lh_<type>\fI_free()\fR, lh_<type>\fI_doall()\fR and lh_<type>\fI_doall_arg()\fR return no values. +.SH "NOTE" +.IX Header "NOTE" +The various \s-1LHASH\s0 macros and callback types exist to make it possible +to write type-checked code without resorting to function-prototype +casting \- an evil that makes application code much harder to +audit/verify and also opens the window of opportunity for stack +corruption and other hard-to-find bugs. It also, apparently, violates +ANSI-C. +.PP +The \s-1LHASH\s0 code regards table entries as constant data. As such, it +internally represents \fIlh_insert()\fR'd items with a \*(L"const void *\*(R" +pointer type. This is why callbacks such as those used by \fIlh_doall()\fR +and \fIlh_doall_arg()\fR declare their prototypes with \*(L"const\*(R", even for the +parameters that pass back the table items' data pointers \- for +consistency, user-provided data is \*(L"const\*(R" at all times as far as the +\&\s-1LHASH\s0 code is concerned. However, as callers are themselves providing +these pointers, they can choose whether they too should be treating +all such parameters as constant. +.PP +As an example, a hash table may be maintained by code that, for +reasons of encapsulation, has only \*(L"const\*(R" access to the data being +indexed in the hash table (ie. it is returned as \*(L"const\*(R" from +elsewhere in their code) \- in this case the \s-1LHASH\s0 prototypes are +appropriate as-is. Conversely, if the caller is responsible for the +life-time of the data in question, then they may well wish to make +modifications to table item passed back in the \fIlh_doall()\fR or +\&\fIlh_doall_arg()\fR callbacks (see the \*(L"STUFF_cleanup\*(R" example above). If +so, the caller can either cast the \*(L"const\*(R" away (if they're providing +the raw callbacks themselves) or use the macros to declare/implement +the wrapper functions without \*(L"const\*(R" types. +.PP +Callers that only have \*(L"const\*(R" access to data they're indexing in a +table, yet declare callbacks without constant types (or cast the +\&\*(L"const\*(R" away themselves), are therefore creating their own risks/bugs +without being encouraged to do so by the \s-1API\s0. On a related note, +those auditing code should pay special attention to any instances of +DECLARE/IMPLEMENT_LHASH_DOALL_[\s-1ARG_\s0]_FN macros that provide types +without any \*(L"const\*(R" qualifiers. +.SH "BUGS" +.IX Header "BUGS" +lh_<type>\fI_insert()\fR returns \fB\s-1NULL\s0\fR both for success and error. +.SH "INTERNALS" +.IX Header "INTERNALS" +The following description is based on the SSLeay documentation: +.PP +The \fBlhash\fR library implements a hash table described in the +\&\fICommunications of the \s-1ACM\s0\fR in 1991. What makes this hash table +different is that as the table fills, the hash table is increased (or +decreased) in size via \fIOPENSSL_realloc()\fR. When a 'resize' is done, instead of +all hashes being redistributed over twice as many 'buckets', one +bucket is split. So when an 'expand' is done, there is only a minimal +cost to redistribute some values. Subsequent inserts will cause more +single 'bucket' redistributions but there will never be a sudden large +cost due to redistributing all the 'buckets'. +.PP +The state for a particular hash table is kept in the \fB\s-1LHASH\s0\fR structure. +The decision to increase or decrease the hash table size is made +depending on the 'load' of the hash table. The load is the number of +items in the hash table divided by the size of the hash table. The +default values are as follows. If (hash\->up_load < load) => +expand. if (hash\->down_load > load) => contract. The +\&\fBup_load\fR has a default value of 1 and \fBdown_load\fR has a default value +of 2. These numbers can be modified by the application by just +playing with the \fBup_load\fR and \fBdown_load\fR variables. The 'load' is +kept in a form which is multiplied by 256. So +hash\->up_load=8*256; will cause a load of 8 to be set. +.PP +If you are interested in performance the field to watch is +num_comp_calls. The hash library keeps track of the 'hash' value for +each item so when a lookup is done, the 'hashes' are compared, if +there is a match, then a full compare is done, and +hash\->num_comp_calls is incremented. If num_comp_calls is not equal +to num_delete plus num_retrieve it means that your hash function is +generating hashes that are the same for different values. It is +probably worth changing your hash function if this is the case because +even if your hash table has 10 items in a 'bucket', it can be searched +with 10 \fBunsigned long\fR compares and 10 linked list traverses. This +will be much less expensive that 10 calls to your compare function. +.PP +\&\fIlh_strhash()\fR is a demo string hashing function: +.PP +.Vb 1 +\& unsigned long lh_strhash(const char *c); +.Ve +.PP +Since the \fB\s-1LHASH\s0\fR routines would normally be passed structures, this +routine would not normally be passed to lh_<type>\fI_new()\fR, rather it would be +used in the function passed to lh_<type>\fI_new()\fR. +.SH "SEE ALSO" +.IX Header "SEE ALSO" +\&\fIlh_stats\fR\|(3) +.SH "HISTORY" +.IX Header "HISTORY" +The \fBlhash\fR library is available in all versions of SSLeay and OpenSSL. +\&\fIlh_error()\fR was added in SSLeay 0.9.1b. +.PP +This manpage is derived from the SSLeay documentation. +.PP +In OpenSSL 0.9.7, all lhash functions that were passed function pointers +were changed for better type safety, and the function types \s-1LHASH_COMP_FN_TYPE\s0, +\&\s-1LHASH_HASH_FN_TYPE\s0, \s-1LHASH_DOALL_FN_TYPE\s0 and \s-1LHASH_DOALL_ARG_FN_TYPE\s0 +became available. +.PP +In OpenSSL 1.0.0, the lhash interface was revamped for even better +type checking. |
