Linked by Dennis Heuer on Wed 25th Aug 2010 22:23 UTC
Linux I came across a news entry at Phoronix about a new init replacement, systemd, and curiously started a read into the surprisingly heavy matter. Systemd is by no means as simple as upstart. It does far more things far more straight and in more detail. The differences are so significant that they enforce quite different configuration strategies. One can argue for both, depending on the goal to reach. However, that's not what I want to write about. After having read what systemd is capable of, and how it does it, I began to put the existence of all system daemons - in their today's forms - in question.
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Author need to read Bugs completely.
by oiaohm on Sat 28th Aug 2010 04:03 UTC
oiaohm
Member since:
2009-05-30

https://bugzilla.redhat.com/show_bug.cgi?id=615527

If this was fully read you would notice Eric Paris the lead of fanotify. The lead developer to the replacement to inotify and dnotify. fanotify has none of the issues of inotify.

In fact fanotify allows you to block accept and delay requests of a file system. Something the past inotify and dnotify don't allow. Reason fanotify support real-time virus scanning and auditing from user-space.

Not all forms of auditing can be done from kernel space. Like who in there right mind would run a virus scan in kernel space.

"For example, if systemd recognizes a mountpoint access, it can mount the resource immediately. But, is that quick enough? Systemd has no influence on the accessing process and thus can't turn it into sleep until the mount happened."

This so call issue can be solved by fanotify delay response putting application to sleep. fanotify needs to feature complete then problem here is solved.

Next systemd uses cgroups to divide tasks. A full cgroup can be suspended while waiting for a drive to mount as well. Little over the top. fanotify catching would be far less painful.

There are a few experiments in using fanotify to make file recovery from backup transparent. Ie when you attempt to access file that has been sent to backup program gets delayed until file is recovered from backup location and extracted.

systemd is setting up to take advantage of the tech that will be on hand to userspace for auditing over the next 12 months. This really does leave all the other init systems far behind.

cgroup tech is also always expanding. The control systemd is providing compared to all the old systems is many times more.

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