Stephen's Work Ramblings

The LCFG client has a, slightly weird, feature called “secure mode“. This makes the client hold off applying any resource changes until they have been manually reviewed. The manual checking is done by examining the contents of a “hold file” which shows the differences in values for each modified resource in a simple text form. The file also contains a “signature” which is the MD5 digest (in hex) of the changes. A change set is applied manually by passing that signature to the client which then regenerates the hold file and compares that signature with the one supplied. This is not a heavily used feature of the client but it is something we want to support in the new LCFG profile framework. The new framework has built-in support for diffing the data structures which represent LCFG profiles, components and resources. This makes it relatively straightforward to add a feature which generates the secure-mode hold file when required, the only awkward part was finding some code to do the MD5 digest in a nice way.

Here’s an example using the C API, error checking and suchlike has been dropped to keep it simple.

#include <lcfg/profile.h>
#include <lcfg/bdb.h>
#include <lcfg/differences.h>

int main(void) {

char * msg = NULL;

LCFGProfile * p1 = NULL;
lcfgprofile_from_status_dir( “/run/lcfg/status”,
&p1, NULL, &msg );

LCFGProfile * p2 = NULL;
lcfgprofile_from_bdb( “/var/lcfg/conf/profile/dbm/example.lcfg.org.DB2.db”,
&p2, NULL, 0, &msg );

LCFGDiffProfile * diff = NULL;
lcfgprofile_diff( p1, p2, &diff, &msg );

char * signature = NULL;
lcfgdiffprofile_to_holdfile( diff, “/tmp/holdfile”, &signature, &msg );

lcfgprofile_destroy(p1);
lcfgprofile_destroy(p2);
lcfgdiffprofile_destroy(diff);

free(msg);

return 0;
}