[plugins] speedup journal collection (v2)

[champtar]

Instead of generating all the logs and tailing the last 100M, we get the first 100M of 'journalctl --reverse' that we then reverse again using our own implementation of tac.

To handle multiline logs we would need to use "tac -brs '^[^ ]'" that takes ~30s on 100M of logs when plain 'tac' takes ~0.3s. Our simple implementation in python takes 0.7s, and avoid an extra dependency.

On journalctl timeout we now get the most recents logs.

During collection logs are now buffered on disk, so we use 2xsizelimit. While running our tac we could actually truncate the source file to limit disk usage. Previously buffering was in RAM (also 2xsizelimit).

On my test server, logs plugin runtime goes from 34s to 9.5s.

Fixes #3615

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[packit-as-a-service]

Congratulations! One of the builds has completed. 🍾

You can install the built RPMs by following these steps:

• sudo yum install -y dnf-plugins-core on RHEL 8
• sudo dnf install -y dnf-plugins-core on Fedora
• dnf copr enable packit/sosreport-sos-3879
• And now you can install the packages.

Please note that the RPMs should be used only in a testing environment.

[pmoravec]

I can confirm VERY evident speedup on a tested RHEL8 system with:

# journalctl --disk-usage 
Archived and active journals take up 560.0M in the file system.
#

where current upstream executes python3 bin/sos report -o logs --batch --build in 18s and this PR shrinks it to 3s.

Some test is failing - can you @champtar review it or do you need some help? I might get to the failure later today /tomorrow.

[pmoravec]

Missing leading f as you use f-string :)

[champtar]

I'm off until the 27th so no rush for the review, and I was thinking about even implementing 'head' in Python

[pmoravec]

tests/report_tests/plugin_tests/defaults.py:40:            if cmd['exec'] == 'journalctl --no-pager  --unit cups':

needs to be updated to reflect changed command exec "sh -c 'journalctl --no-pager --unit cups --reverse | head -c 104857600'" - I vote for 'journalctl --no-pager --unit cups' in cmd['exec'] test.

The 2-tests/report_tests/plugin_tests/logs.py:JournalSizeLimitTest.test_journal_tailed_and_linked failure: The PR breaks part of tailit functionality: when a command output is bigger than --log-size (or --journal-size here), sosreport looks like:

# ll /var/tmp/sosreport-pmoravec-rhel9-8675309-2024-12-18-dusvggk/sos_commands/logs/
total 24
-rw-r--r--. 1 root root    63 Dec 18 15:50 journalctl_--disk-usage
lrwxrwxrwx. 1 root root    51 Dec 18 15:50 journalctl_--no-pager -> ../../sos_strings/logs/journalctl_--no-pager.tailed
lrwxrwxrwx. 1 root root    58 Dec 18 15:50 journalctl_--no-pager_--boot -> ../../sos_strings/logs/journalctl_--no-pager_--boot.tailed
-rw-r--r--. 1 root root    82 Dec 18 15:50 journalctl_--no-pager_--boot_-1
-rw-r--r--. 1 root root 13355 Dec 18 15:50 ls_-alRh_.var.log
# ll /var/tmp/sosreport-pmoravec-rhel9-8675309-2024-12-18-dusvggk/sos_strings/logs/
total 24824
-rw-r--r--. 1 root root 10484923 Dec 18 15:50 journalctl_--no-pager_--boot.tailed
-rw-r--r--. 1 root root 10484923 Dec 18 15:50 journalctl_--no-pager.tailed
-rw-r--r--. 1 root root  4445393 Dec 18 15:50 var.log.messages-20241201.tailed
#

And manifest.json tracks that via "truncated": true,.

With this PR, I see:

# ll /var/tmp/sosreport-pmoravec-rhel9-8675309-2024-12-18-zagarel/sos_commands/logs/
total 20464
-rw-r--r--. 1 root root       63 Dec 18 15:50 journalctl_--disk-usage
-rw-r--r--. 1 root root 10460043 Dec 18 15:50 journalctl_--no-pager
-rw-r--r--. 1 root root 10460043 Dec 18 15:50 journalctl_--no-pager_--boot
-rw-r--r--. 1 root root       82 Dec 18 15:50 journalctl_--no-pager_--boot_-1
-rw-r--r--. 1 root root    22730 Dec 18 15:50 ls_-alZR_.var.log
#

That suggests the journalctl outputs are not truncated, which is misleading.