Bug 86855 - Reading journal backwards misses entries
Summary: Reading journal backwards misses entries
Alias: None
Product: systemd
Classification: Unclassified
Component: general (show other bugs)
Version: unspecified
Hardware: Other All
: medium major
Assignee: systemd-bugs
QA Contact: systemd-bugs
Depends on:
Reported: 2014-11-29 16:39 UTC by Olivier Brunel (jjacky)
Modified: 2014-12-08 18:24 UTC (History)
1 user (show)

See Also:
i915 platform:
i915 features:


Description Olivier Brunel (jjacky) 2014-11-29 16:39:44 UTC
Simple illustration of the problem:

% coredumpctl list COREDUMP_PID=8212   
TIME                            PID   UID   GID SIG PRESENT EXE
Sat 2014-11-29 13:17:03 CET    8212  1000   100   6 * /usr/bin/Xorg.bin

% coredumpctl list -1 COREDUMP_PID=8212
No match found.

The reason it fails to find a match with -1 is that then sd_journal_seek_tail()/sd_journal_previous() are used, else it's be seek_head()/next(); and apparently going backwards doen't work right.

As a test, I did a small program that uses similar matches (COREDUMP_PID=8212 AND MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1), if the loop with the call to sd_journal_get_data() is done with SD_JOURNAL_FOREACH(j) it works, with SD_JOURNAL_FOREACH_BACKWARDS(j) no matches are found.

Trying using another set of matches (on a COREDUMP_EXE this time), I get 13 matches going forward, only 12 going backwards.

No idea what's going on, but clearly going backwards in the journal doesn't work properly.

This is on up-to-date Arch Linux x86_64:
% systemctl --version
systemd 217
Comment 1 Lennart Poettering 2014-12-08 18:24:32 UTC
Fixed in git, with your patch! Thanks!

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