doc/image_format: Modernize

The content was mostly referring to how things were initially set up for containers with minimal updates made for virtual machines. This reworks the image format descriptions to match how things currently work. Closes #668 Signed-off-by: Stéphane Graber <[email protected]>
lxc · Mar 26, 2024 · 1c8adda · 1c8adda
1 parent 11bb355
commit 1c8adda
Showing 1 changed file with 8 additions and 6 deletions.
diff --git a/doc/reference/image_format.md b/doc/reference/image_format.md
@@ -151,14 +151,16 @@ The image identifier for such images is the SHA-256 of the tarball.
 (image-format-split)=
 ### Split tarballs
 
-A split image consists of two separate tarballs.
-One tarball contains the metadata and optionally the template files (usually `*.tar.xz`), and the other contains the root file system (usually `*.squashfs` for containers or `*.qcow2` for virtual machines).
+A split image consists of two files.
+The first is a tarball containining the metadata and optionally the template files (usually `*.tar.xz`).
+The second can be a tarball, `squashfs` or `qcow2` image containing the actual instance data.
 
-For containers, the root file system tarball can be SquashFS-formatted.
-For virtual machines, the `rootfs.img` file always uses the `qcow2` format.
-It can optionally be compressed using `qcow2`'s native compression.
+For containers, the second file is most commonly a SquashFS-formatted file system tree, though it can also be a tarball of the same tree.
+For virtual machines, the second file is always a `qcow2` formatted disk image.
+
+Tarballs can be externally compressed (`.tar.xz`, `.tar.gz`, ...) whereas `squashfs` and `qcow2` can be internally compressed through their respective native compression options.
 
 This format is designed to allow for easy image building from existing non-Incus rootfs tarballs that are already available.
 You should also use this format if you want to create images that can be consumed by both Incus and other tools.
 
-The image identifier for such images is the SHA-256 of the concatenation of the metadata and root file system tarball (in that order).
+The image identifier for such images is the SHA-256 of the concatenation of the metadata and data filesl (in that order).