[systemd-devel] [PATCH v2 5/5] mount: auto-detect iSCSI and FCoE as requiring network

[Karel Zak]

On Fri, Nov 28, 2014 at 09:27:43PM +0100, Lennart Poettering wrote:
> On Fri, 28.11.14 20:50, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:
> 
> > On Sun, Nov 23, 2014 at 08:33:41PM -0800, Chris Leech wrote:
> > > This adds auto detection for iSCSI and some FCoE drivers and treats
> > > mounts to file-systems on those devices as remote-fs.
> > > 
> > > Signed-off-by: Chris Leech <cleech at redhat.com>
> > No need for this.
> > 
> > I now pushed patches 1-4 with some small changes here and there.
> > Since libmount is not optional, I removed if from the version string.
> > 
> > This patch I didn't push: this seems like something that would be better
> > done through udev rules, by setting some tags. Then systemd could simply
> > check for the presence of a tag on the device without having any
> > special knowledge about iscsi and firends.
> 
> Honestly, I am really not sure I like this patch.
> 
> One one hand we now have a hard dep on libmount. Which I figure is
> mostly OK. However, what I find really weird about this is that even
> though libmount is supposed to abstract access to the "utab" away, it
> doesn't sufficiently: we still hardcode the utab path now so that we
> can watch it. I mean, either we use an abstracted interface or we
> don't. THis really smells to me as either libmount should provide some
> form of inotify iface to utab, or we should parse utab directly. If
> libmount is the only and official API for utab, then we should
> that. If the utab file however is API too, then we can well go ahead
> and parse it directly.

I'd like to keep the utab file private. The whole libmount API is
abstraction and completely hides the difference between original
/etc/mtab and new /run/mount/utab.

The original Chris' purpose for the patches has been _netdev, it
means to improve detection of dependence between filesystem and
network. I still believe that the right way is to check for network
block devices than rely on crazy _netdev userspace mount option.

Wouldn't be enough to use Chris' iSCSI and FCoE auto detection?

Or we can add udev rule to have NET_DEVBLK tag in udevdb, or maybe we
can ask kernel developers to add /sys/block/sdb/network (as we already
have "removable" in /sys).

Chris, why do you want both ways (utab and the auto detection)? 

IMHO it would be really nice to completely kill _netdev in systemd
universe ;-) It's legacy from shell init scripts.


Anyway, if you still want to read userspace mount options than I can
add something like:

 mnt_inotify_mtab_add_watch()
 mnt_inotify_mtab_rm_watch()
 mnt_inotify_mtab_changed()

to hide all the paths and private mtab/utab stuff.

> THe new code looks also buggy to me. For example, am I missing
> something or is nobody creating /run/mount? I mean, we need to make
> sure that it exists before we can install an inotify watch on it.

yep, it should be hidden within libmount

> Also, it leaves the cescape() calls in for what we read from libmount,
> which makes a lot of alarm bells ring in my head: doesn't libmount do
> that on its own?

sure, libmount encodes/decodes all when read/write the files.

    Karel

-- 
 Karel Zak  <kzak at redhat.com>
 http://karelzak.blogspot.com