journalctl: Add support for showing messages from a previous boot

Hi,

I redid the boot ID look up to use enumerate_unique.

This is quite fast if the cache is warm but painfully slow if
it isn't. It has a slight chance of returning the wrong order if
realtime clock jumps around.

This one has to do n searches for every boot ID there is plus
a sort, so it depends heavily on cache hotness. This is in contrast
to the other way of look-up through filtering by a MESSAGE_ID,
which only needs about 1 seek + whatever amount of relative IDs
you want to walk.

I also have a linked-list + (in-place) mergesort version of this
patch, which has pretty much the same runtime. But since this one
is using libc sorting and armortized allocation, I prefer this
one.

To summarize: The MESSAGE_ID way is a *lot* faster but can be
incomplete due to rotation, while the enumerate+sort will find
every boot ID out there but will be painfully slow for large
journals and cold caches.

You choose :P

Jan

1 files changed, 0 insertions, 1 deletions

diff --git a/TODO b/TODO
index 10f2b74df2..f5da81f527 100644
--- a/TODO
+++ b/TODO
@@ -356,7 +356,6 @@ Features:
   - journal-send.c, log.c: when the log socket is clogged, and we drop, count this and write a message about this when it gets unclogged again.
   - journal: find a way to allow dropping history early, based on priority, other rules
   - journal: When used on NFS, check payload hashes
-  - Introduce journalctl -b <nr> to show journal messages of a previous boot
   - journald: check whether it is OK if the client can still modify delivered journal entries
   - journal live copy, based on libneon (client) and libmicrohttpd (server)
   - journald: add kernel cmdline option to disable ratelimiting for debug purposes