docs: extend object type documentation

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>

diff --git a/docs/manual/repo.md b/docs/manual/repo.md
index 08fd5fe2ee53b02f9e3c073ff34216a9c8b242b3..b8c3ea5499b81e2256e11c852b399b9c109753d5 100644 (file)
--- a/docs/manual/repo.md
+++ b/docs/manual/repo.md
@@ -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