If a system administrator happens to type `ostree admin upgrade`
multiple times, currently that will lead to a potentially corrupted
system.
I originally attempted to do locking *internally* in `libostree`, but
that didn't work out because currently a number of the commands
perform multi-step operations that all need to be serialized. All of
the current code in `ostree admin deploy` is an example.
Therefore, allow callers to perform locking, as most of the higher
level logic is presently implemented there.
At some point, we can revisit having internal locking, but it will be
difficult. A more likely approach would be similar to Java's approach
with concurrency on iterators - a "fail fast" method.
These fsyncs were added for what turned out to be a fairly bogus
reason; I was hitting read errors from extlinux after upgrades and out
of conservatisim tried adding fsync calls, but the *actual* problem
was that extlinux didn't support 64 bit ext4. Now that at least for
Project Atomic hosts we're just targeting grub2, we can drop these
fsync calls and rely on `syncfs()` being both faster and catching any
errors.
I was looking at https://bugzilla.gnome.org/show_bug.cgi?id=738954
which wants us to ensure we chown() the refs. As part of that,
I did a generic conversion to use `*at()` (which naturally gives
us more low level control so we can call `fchown` etc.
This patch also sneaks in a change to respect the repo's
`disable_fsync` flag - if fsync is not set, then we never
`fdatasync()` (unlike the `g_file_replace_contents()` default. Also
unlike it, if fsync is enabled, we *always* sync even if the file
didn't exist.
Starting down the path of not using libgsystem. The main win here
will be code sharing between ostree/rpm-ostree as well as going down
the path of not using GFile * for local files.
Colin Walters
Matthew Barnes
Daniel Svensson