Bug 1415451

This should work if I understand ostree correctly.  The %post scriptlet writes to sysconfdir, but that should be okay, I think.  Given that the error comes from bwrap, I'm assuming that this is an rpm-ostree bug.

Feel free to assign back to fish if there's something that fish could do better.

This is another instance of https://bugzilla.redhat.com/show_bug.cgi?id=1367587 but for fish.

Andy, see https://bugzilla.redhat.com/show_bug.cgi?id=1352154#c0 for more information.

I suppose I could work around this in fish, but: could rofiles-fuse learn about O_APPEND?  The current scriptlet in fish follows the packaging guideline's recommendation (or at least it did) and works more or less atomically.

Also, will %postun have the same problem?

I think with O_APPEND one could still get corrupted config files if interrupted halfway, and obviously a corrupted /etc/shells would be bad.  So it's just general best practice to do the "atomic file replace" pattern.

I'll see about getting the guidelines changed.

As far as %postun - rpm-ostree doesn't run them and likely never will.  Removing a package is constructing a new tree where that package isn't present.  In general, a major goal of rpm-ostree is to be anti-hysteresis <https://en.wikipedia.org/wiki/Hysteresis>

I think I disagree for technical reasons.

For atomic-file-replace, the scriptlet will do, roughly:

cp /etc/shells /tmp/foo
echo whatever >>/tmp/foo
mv -f /tmp/foo /etc/shells

With O_APPEND support, that would change to:

open("/etc/shells", O_APPEND | ...);
# The FUSE helper copies the file and returns a writable fd
write(...);

In either case, if a different process writes to the file in between the copy and the replace, that write will get lost.  If nothing else writes to the file, everything is fine.  As a practical matter, the actual behavior should be essentially identical in both variants.

Also, actually making the change to the scriptlet seems likely to be a bit of a pain.  I would want to make sure that, on non-ostree systems, the mode, label, etc of /etc/shells isn't changed by the scriptlet.  This is a bit awkward.

I completely agree that we could make that change in rofiles-fuse.  In fact, that would take us farther down the "more like overlayfs" path.

But if you look at the evolution of overlayfs, there are some really awful hacks there due to it doing in kernel space what IMO is clearly better done in userspace.

See e.g. http://marc.info/?l=linux-fsdevel&m=148458878412049&w=2

(FTR, I'd like to not rely on FUSE either, but rather have http://www.spinics.net/lists/linux-fsdevel/msg75085.html )

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Still applicable with F27.

This bug appears to have been reported against 'rawhide' during the Fedora 28 development cycle.
Changing version to '28'.

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more recent Fedora release includes newer upstream software that fixes 
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I never tested this in Fedora 29 (the last OSTree-based release to still be called Atomic Host), but `sudo rpm-ostree install fish` works fine for me in a virtual machine of Fedora 30 Silverblue.

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