Automatically save solver testcase

[lslezak]

Problem

• Debugging dependency problems is difficult without knowing the details

Solution

• Automatically save the solver testcase when the solver run fails.
• For debugging purposes allow saving the testcase even on solver success when the inst.solver_testcase=1 boot option is used. This can help debugging problems where the solver does not fail but some optional packages are not automatically installed (like kernel drivers, firmware packages, language packages...).
• Include the solver testcase in the logs saved using the agama logs store command.

Notes

• Saving the solver testcase is quite expensive (takes ~1.3s in Tumbleweed on a very fast machine, not that much but it needs to run several times during the Agama configuration phase). It also takes some storage space (=RAM in Live ISO!), about 9MB in Tumbleweed and about 2.5MB in SLES.
• To avoid wasting resources a solver test case is saved only when the solver fails or when explicitly requested with the inst.solver_testcase=1 boot option.

Testing

• Tested manually

# journalctl -u agama-web-server.service | grep "testcase saved"
Mar 05 12:23:50 agama-tw agama-web-server[3142]: Solver testcase saved to /var/log/zypp/testcase, elapsed time: 1.307023323s
Mar 05 12:23:52 agama-tw agama-web-server[3142]: Solver testcase saved to /var/log/zypp/testcase, elapsed time: 1.304726128s
Mar 05 12:23:53 agama-tw agama-web-server[3142]: Solver testcase saved to /var/log/zypp/testcase, elapsed time: 1.360524222s
# ls -lh /var/log/zypp/testcase/
total 8.9M
-rw-r--r-- 1 root root   30 Mar  5 12:23 @System.repo.gz
-rw-r--r-- 1 root root 8.8M Mar  5 12:23 agama-0.repo.gz
-rw-r--r-- 1 root root 5.6K Mar  5 12:23 agama-1.repo.gz
-rw-r--r-- 1 root root 1.2K Mar  5 12:23 agama-2.repo.gz
-rw-r--r-- 1 root root  37K Mar  5 12:23 solver.result
-rw-r--r-- 1 root root 5.5K Mar  5 12:23 testcase.t
-rw-r----- 1 root root 3.6K Mar  5 12:23 y2log
-rw-r--r-- 1 root root 6.1K Mar  5 12:23 zypp-control.yaml
-rw-r--r-- 1 root root 2.6K Mar  5 12:23 zypp-modalias.yaml

TODO

• Document the inst.solver_testcase=1 boot option

[imobachgs]

I think we should have a struct to hold configuration options like only_required, save_solver_testcase, etc. But that's out of scope here.

[mlandres]

@lslezak Frankly I'd vote for something like /var/log/agama.solverTestCase (like /var/log/zypper.solverTestCase).
The /var/log/zypp directory is not intended to be used by applications and we (libzypp) think about giving it up in the future. The history file there will probably be moved to a location snapshoted and restored by Transactional.