Re: [PATCH v2 5/5] compact: provide user more information on after-compaction failures

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+From: Tomi Ollila <tomi.ollila@iki.fi>\r
+To: David Bremner <david@tethera.net>, Jani Nikula <jani@nikula.org>,\r
+       notmuch@notmuchmail.org\r
+Subject: Re: [PATCH v2 5/5] compact: provide user more information on\r
+       after-compaction failures\r
+In-Reply-To: <87y54rx8sf.fsf@unb.ca>\r
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+       <871u2jnkai.fsf@nikula.org> <87y54rx8sf.fsf@unb.ca>\r
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+Date: Thu, 14 Nov 2013 19:23:14 +0200\r
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+\r
+On Thu, Nov 14 2013, David Bremner <david@tethera.net> wrote:\r
+\r
+> Jani Nikula <jani@nikula.org> writes:\r
+>\r
+>> On Wed, 13 Nov 2013, Tomi Ollila <tomi.ollila@iki.fi> wrote:\r
+>>> After database has been compacted, there are steps to put the new\r
+>>> database into place -- and these steps may fail. In case such\r
+>>> failure happens, provide better information how to resolve it.\r
+>>\r
+>> I disagree with having a library spew all this information out. For each\r
+>> case, I think it should be sufficient to just say what happened\r
+>> (e.g. "rename a -> b failed" + strerror). I don't think a library's\r
+>> error messages should be a tutorial on how to fix things.\r
+>>\r
+>\r
+> I can live with whatever the concensus level of verbosity, but not the\r
+> fprintf's; as I mentioned, for once we have a log hook.\r
+\r
+Jani is right there that *library* should not dump all that info\r
+to ... stderr. If so much info is printed, the client code should\r
+do that -- but doing that cleanly is not a trivial job. The idea of\r
+amending the namual page to inform user is a good one.\r
+\r
+The log hook in it's current form is problematic as it doesn't provide\r
+way to distinguish progress reporting from error reporting. Currently\r
+lib/database.cc writes error messages with fprintf(stderr, ...) everywhere.\r
+\r
+I suggest that this problem is fixed in one big sweep during 0.18\r
+development -- the suggestion Jani pastebin'd a few days ago is\r
+a good one and I'm willing to take part of that development...\r
+And now take this approach of fprintf()ing (basically I would\r
+also ask developers using the library wait for 0.18 before starting\r
+to use the compact functionality (if ever), as the we have yet\r
+another soname bump with changing interface coming...\r
+\r
+\r
+Just that the log interface needs to be in format\r
+\r
+void (*log_cb)(void * closure, int level, const char * message)\r
+\r
+And we need to decide between the (non-NIH) syslog levels vs.\r
+our own levels...\r
+\r
+This way we can distinguish debug (DEBUG), progress (NOTICE, INFO) \r
+and error (WARN, EER, CRIT, ALERT, EMERG) conditions.\r
+\r
+\r
+For someone who wished logf(closure, level, fmt, ...) we can provide\r
+helper functions\r
+\r
+_log_printf(log_cb, closure, level, fmt, ...) and\r
+_log_vprintf(log_cb, closure, level, fmt, ap)\r
+\r
+\r
+>\r
+> That might also somewhat comfort Jani, since the library client has the\r
+> option of ignoring the spewing.\r
+\r
+String maybe!\r
+\r
+>\r
+> d\r
+\r
+Tomi\r
+\r