We had code to deal with opening/checksumming/decompressing static
deltas in a few places. I'd like to teach `ostree static-delta show`
how to display more information, and this will allow it to just use
`_ostree_static_delta_part_open()` too.
Right now though, almost all of the details of deltas are private, so
we can't do the "honest thing" and have the command line just use the
shared library.
Eventually some of this should appear in the API, but for now add
command line which is useful for debugging.
The previous diff algorithm was file tree based, and only looked
at modified files that lived at the same path.
However, components like the Linux kernel have versioned
subdirectories, e.g. /usr/lib/modules/$kver/.../ext4.ko. We want to
be able to detect these "modified renames" so that we can compute
diffs (rollsum, bsdiff).
This does an rsync-style prepared delta basically. On my test data,
it shaves ~6MB of uncompressed data. Not a huge amount, but I expect
this to be more useful for things like binaries which embed data, etc.
There's still some silliness here, but there is now only one opcode
open-splice-and-close, that writes a single chunk from the payload.
This is really all we need for metadata, and small content objects are
also fine with this.
We get some deduplication between content objects by creating a
dictionary for (uid,gid,mode) tuples and xattrs.
This still keeps the operation/payload code in, so we could do
rollsums in a future update easily.
This has a very basic level of functionality (deltas can be generated,
and applied offline). There is only some stubbed out pull code to
fetch them via HTTP.
But, better to commit this now and improve it from a known starting
point, rather than have it languish in a branch.
Colin Walters
Alexander Larsson
Giuseppe Scrivano