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docs: extend object type documentation

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Extend the object type documentation with file endings used for the
individual type. Also clarify in which situation content type objects
are used and why they do not match the SHA256 hash today.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
This commit is contained in:
Stefan Agner 2020-04-24 13:05:15 +02:00
parent b7662aaf33
commit b43c0be347
1 changed files with 11 additions and 2 deletions
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13
docs/manual/repo.md
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@ -31,13 +31,16 @@ regenerate it from source code.
A dirtree contains a sorted array of (filename, checksum)
pairs for content objects, and a second sorted array of
(filename, dirtree checksum, dirmeta checksum), which are
subdirectories.
subdirectories. These type of objects are stored as files
ending with `.dirtree` in the objects directory.
### Dirmeta objects
In git, tree objects contain the metadata such as permissions
for their children. But OSTree splits this into a separate
object to avoid duplicating extended attribute listings.
These type of objects are stored as files ending with `.dirmeta`
in the objects directory.
### Content objects
@ -45,7 +48,13 @@ Unlike the first three object types which are metadata, designed to be
`mmap()`ed, the content object has a separate internal header and
payload sections. The header contains uid, gid, mode, and symbolic
link target (for symlinks), as well as extended attributes. After the
header, for regular files, the content follows.
header, for regular files, the content follows. These parts toghether
form the SHA256 hash for content objects. The content type objects in
this format exist only in `archive` OSTree repositories. Today the
content part is gzip'ed and the objects are stored as files ending
with `.filez` in the objects directory. Because the SHA256 hash is
formed over the uncompressed content, these files do not match the
hash they are named as.
The OSTree data format intentionally does not contain timestamps. The reasoning
is that data files may be downloaded at different times, and by different build