First, move deployments to /ostree/deploy. Having them in the
toplevel clutters the filesystem layout too much.
When we deploy a tree like /ostree/deploy/NAME, there is now also a
writable directory /ostree/deploy/NAME-etc. This is mounted as
read-write inside the system.
On an initial install, that directory is copied from
/ostree/deploy/NAME/etc. On subsequent deployments, we find any
changes made in the current deployment's /etc, and apply that set of
changes to the new deployment's /etc.
See https://live.gnome.org/OSTree/EverythingInEtcIsABug
I run builds on my laptop, but it also crashes about 1/4 of the time
while suspending. It's definitely undesrirable to get e.g. empty
.dirtree objects because they corrupt builds. Concretely, I was
getting empty contents committed for xorg-util-macros.
Now, we used to write out temporary files using g_file_replace() which
does a fsync() during close, but then switched to a more "manual"
g_file_append_to().
We could switch back to g_file_replace(), but the problem is, we don't
want to call fsync() on temporary files in the case where we already
have the object. Attempting to add an object we already have is a
*very* common case.
This is both the old and new code sequence for the case where an
object is already stored:
open(temp, O_WRONLY)
write() write() write()
close()
lstat(objects/3a/9fe332...) = 0
unlink(temp)
In the *new* code, here's the case where an object *isn't* stored:
open(temp, O_WRONLY)
write() write() write()
close()
lstat(objects/3a/9fe332...) = -1
open(temp, O_RDONLY)
fdatasync()
close()
rename(temp, objects/3a/9fe332)
Compare with the *old* code path for when an object isn't stored:
open(temp, O_WRONLY)
write() write() write()
close()
lstat(objects/3a/9fe332...) = -1
link(temp, objects/3a/9fe332)
unlink(temp)
The problem with this is we really need to fdatasync(). Also doing
just rename() instead of the weird link()/unlink() helps us express to
the filesystem that we want atomic semantics. For example, BTRFS has
special handling for rename().
We really don't have a sane story for private files. This is a
defensive step ensuring that with old versions of gnome-ostree,
components that mistakenly have un-world-readable files don't break
pulls.
As the manual page doesn't say, but the in-code kernel documentation
shows, hardlinking for normal users can fail for a variety of
reasons (including very common situations such as non regular file
or non writable file), if the owner of the file does not match
the user linking (e.g. when checking out a shadow repo with a root-
owned master).
If that happens, fail back silently to copying instead of aborting
the whole operation.
https://bugzilla.gnome.org/show_bug.cgi?id=682298
This helps make things less confusing when we try to create a file not
owned by our uid, such as running ostree-pull as non-root on a
repository owned by root.
This can be a large performance win in certain circumstances:
* Cold buffer cache (we don't block the whole process)
* Requiring a copy instead of hardlink
The previous fix to just ignore symbolic links for hard linking isn't
really good enough, since it can happen for empty files too.
Since this is an optimization, when we get EMLINK, let's instead just
fall back to copying. This also applies to EXDEV.
Rather than always doing:
1) make temporary link
2) unlink() target
3) rename()
Just try making the link, and only do the second two if the file
already exists. This reduces system call traffic a lot.
By default, when doing a commit, scan all of our loose objects and
build up a (device,inode) -> checksum hash. Then when we're doing a
commit, if we see a file with that (device,inode) pair, we can avoid
checksumming it.
This will allow us to use hard links again for user-mode checkouts,
rather than the hackish link cache. It was pretty silly anyways to
have file objects be stored with just a small metadata header
prepended, but uncompressed.
Either they should be hardlinkable, or compressed (in pack files).
Rather than passing xattr/file_info for all objects, change the API to
assume we're passing the defined object stream for each type. Namely,
for OSTREE_OBJECT_TYPE_FILE, we're now giving the "archive file" data.
This significantly cleans up the code for committing to archive mode
repositories, at the cost of having to (at present) create an
intermediate temporary file when committing to raw repositories.
This will be useful for ostbuild; a user can create their own archive
mode repository which transparently inherits objects from the
root-owned one in /ostree.
Colin Walters
Giovanni Campagna