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diff --git a/resolv/README b/resolv/README deleted file mode 100644 index c50025168c..0000000000 --- a/resolv/README +++ /dev/null @@ -1,152 +0,0 @@ -The resolver in the GNU C Library -********************************* - -Starting with version 2.2, the resolver in the GNU C Library comes -from BIND 8. Only a subset of the src/lib/resolv part of libbind is -included here; basically the parts that are needed to provide the -functionality present in the resolver from BIND 4.9.7 that was -included in the previous release of the GNU C Library, augmented by -the parts needed to provide thread-safety. This means that support -for things as dynamic DNS updates and TSIG keys isn't included. If -you need those facilities, please take a look at the full BIND -distribution. - - -Differences -=========== - -The resolver in the GNU C Library still differs from what's in BIND -8.2.3-T5B: - -* The RES_DEBUG option (`options debug' in /etc/resolv.conf) has been - disabled. - -* The resolver in glibc allows underscores in domain names. - -* The <resolv.h> header in glibc includes <netinet/in.h> and - <arpa/nameser.h> to make it self-contained. - -* The `res_close' function in glibc only tries to close open files - referenced through `_res' if the RES_INIT bit is set in - `_res.options'. This fixes a potential security bug with programs - that bogusly call `res_close' without initialising the resolver - state first. Note that the thread-safe `res_nclose' still doesn't - check the RES_INIT bit. By the way, you're not really supposed to - call `res_close/res_nclose' directly. - -* The resolver in glibc can connect to a nameserver over IPv6. Just - specify the IPv6 address in /etc/resolv.conf. You cannot change the - address of an IPv6 nameserver dynamically in your program though. - - -Using the resolver in multi-threaded code -========================================= - -The traditional resolver interfaces `res_query', `res_search', -`res_mkquery', `res_send' and `res_init', used a static (global) -resolver state stored in the `_res' structure. Therefore, these -interfaces are not thread-safe. Therefore, BIND 8.2 introduced a set -of "new" interfaces `res_nquery', `res_nsearch', `res_nmkquery', -`res_nsend' and `res_ninit' that take a `res_state' as their first -argument, so you can use a per-thread resolver state. In glibc, when -you link with -lpthread, such a per-thread resolver state is already -present. It can be accessed using `_res', which has been redefined as -a macro, in a similar way to what has been done for the `errno' and -`h_errno' variables. This per-thread resolver state is also used for -the `gethostby*' family of functions, which means that for example -`gethostbyname_r' is now fully thread-safe and re-entrant. The -traditional resolver interfaces however, continue to use a single -resolver state and are therefore still thread-unsafe. The resolver -state is the same resolver state that is used for the initial ("main") -thread. - -This has the following consequences for existing binaries and source -code: - -* Single-threaded programs will continue to work. There should be no - user-visible changes when you recompile them. - -* Multi-threaded programs that use the traditional resolver interfaces - in the "main" thread should continue to work, except that they no - longer see any changes in the global resolver state caused by calls - to, for example, `gethostbyname' in other threads. Again there - should be no user-visible changes when you recompile these programs. - -* Multi-threaded programs that use the traditional resolver interfaces - in more than one thread should be just as buggy as before (there are - no problems if you use proper locking of course). If you recompile - these programs, manipulating the _res structure in threads other - than the "main" thread will seem to have no effect though. - -* In Multi-threaded that manipulate the _res structure, calls to - functions like `gethostbyname' in threads other than the "main" - thread won't be influenced by the those changes anymore. - -We recommend to use the new thread-safe interfaces in new code, since -the traditional interfaces have been deprecated by the BIND folks. -For compatibility with other (older) systems you might want to -continue to use those interfaces though. - - -Using the resolver in C++ code -============================== - -There resolver contains some hooks which will allow the user to -install some callback functions that make it possible to filter DNS -requests and responses. Although we do not encourage you to make use -of this facility at all, C++ developers should realise that it isn't -safe to throw exceptions from such callback functions. - - -Source code -=========== - -The following files come from the BIND distribution (currently version -8.2.3-T5B): - -src/include/ - arpa/nameser.h - arpa/nameser_compat.h - resolv.h - -src/lib/resolv/ - herror.c - res_comp.c - res_data.c - res_debug.c - res_debug.h - res_init.c - res_mkquery.c - res_query.c - res_send.c - -src/lib/nameser/ - ns_name.c - ns_netint.c - ns_parse.c - ns_print.c - ns_samedomain.c - ns_ttl.c - -src/lib/inet/ - inet_addr.c - inet_net_ntop.c - inet_net_pton.c - inet_neta.c - inet_ntop.c - inet_pton.c - nsap_addr.c - -src/lib/isc/ - base64.c - -Some of these files have been optimised a bit, and adaptations have -been made to make them fit in with the rest of glibc. - -res_libc.c is home-brewn, although parts of it are taken from res_data.c. - -res_hconf.c and res_hconf.h were contributed by David Mosberger, and -do not come from BIND. - -The files gethnamaddr.c, mapv4v6addr.h and mapv4v6hostent.h are -leftovers from BIND 4.9.7. |