Bug 5357

Currently the interface to bitbake signatures is a bit complex and hard to use. The simple scenario is that you what to know why "bitbake X" is not reusing a given sstate cache.

There are some problems. Specifically, the current sstate cache only has siginfo files for the actual sstate tasks (e.g. populate_sysroot) and not the non-sstate tasks (e.g. fetch/patch/configure/compile/install).

To address this, we probably need to add a bitbake variable which allows dumping the sigdata at the end of every task and we can dump this straight into the sstate directory. The bitbake call needed at the end of each task is  bb.siggen.dump_this_task(xxx.siginfo, d), see sstate.bbclass for how its currently used, we'd trigger this with some kind of new variable for bitbake to notice providing the value of xxx.

Once this is done we can assume the sstate cache directory has all the sigdata. We know the name of the endpoint we want, and all the task start points this would have (X:do_fetch, Y:do_fetch and so on) along with intermediate steps. We'd want to search the sstate cache directory for each task in the tree, we'd likely come up with some matches for some points and others where there was mismatch. We'd then be able to list the possible deviations, ordered from least difference to most difference compared to the current build.

The challenge is therefore to write such a tool and display this data to the user in a way they can understand. They'd probably have to select a deviated tree, then be able to browse the diffsigs for the points.