[RFC/PATCH v3 0/8] readahead: daemon mode

Bartosz Gołaszewski bartekgola at gmail.com
Tue Sep 15 10:19:47 UTC 2015


Hi Denys,

after giving it a thought I would like to ask you to reconsider
merging of the readahead daemon mode.

The reason for implementing this applet is a project we did at
BayLibre - an open-hardware power consumption measurement device:
http://baylibre.com/acme/

It's a cape sitting on top of a BeagleBone Black. The solution is
open-software & open-hardware and the software side is composed of a
custom linux system built by buildroot. We specifically wanted to
provide a full open-source package, and make it possible for ACME
users to build the system from scratch using upstream buildroot. We
actually merged several new packages for buildroot and implemented a
driver for ACME for the sigrok project to achieve that.

While readahead is not mandatory for our system - it improves the user
experience when booting linux with several graphical applications (Qt
based PulseView from the sigrok suite). Keeping it out-of-the-tree
would require us to either: use custom buildroot with different
busybox download path, try to merge a patch containing readahead with
buildroot (for pre-build application) or nuke it altogether. Neither
option is good.

Additional arguments for merging readahead daemon are:
- the readahead applet has been around since 2006, it just wasn't very
useful, since you had to provide the list of files to readahead
manually. This patch does not implement a new applet - merely extend
an existing one,
- not all busybox applets are exact reimplementations of standard
tools: httpd, sendmail, mdev & inotifyd just to name some,
- it doesn't change the default size and doesn't affect any other tools,
- it's backwards compatible with the previous version of readahead.

As for the standarization: I know at least four different readahead
implementations that will never be standarized since they have become
obsolete on desktops after widespread adoption of systemd and SSD
drives. The mechanism is still useful in the embedded world however
for slow eMMC's and - similarly to busybox' httpd - it works without
any configuration file.

Keeping the applet out-of-the-tree basically means that it will get
lost and never used.

Should you agree to merge it, I'll prepare a new series with fixes
from previous reviews.

-- 
Best regards,
Bartosz Golaszewski

PS I promise not to send any non-standard utilities in the future. ;)


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