ubuntu-phone team mailing list archive

[Barry Warsaw <barry@xxxxxxxxxx>]

On Jul 15, 2016, at 12:51 PM, Michał Sawicz wrote:

>system-image-cli always goes to the latest, there's no way to override
>that atm.

Kind of.  As I mentioned earlier, there is the -m/--maximage flag.  Let me
elaborate on that a little bit.

The way s-i works is that it first calculates all the candidate update paths
that the server is offering, from the image number the device is currently on,
to the highest image number in the specified device/channel.  Each of these
three bits can be changed via the command line:

-b - the image number the device thinks it's on
-c - the device's channel
-d - the device's device name

You can see all the candidate paths in the log file or console when you use
--dry-run and -v.

s-i then applies a scoring algorithm to each of the candidate upgrade paths.
For each extra reboot in the upgrade, the path gets +100 (there's always an
implicit reboot at the end, which is not counted).  1 point is added for every
MiB over the size of the path with the smallest total download.  +9000 is
added for the total distance of that path's end point image from the highest
version number available.  All of this strongly weights the winning path to
the smallest delta that leaves you at the highest available version number
with the fewest number of reboots, but other factors can come into play, and
the verbose log will display the sorted candidate paths along with their
scores, from highest score to lowest.

The candidate path with the lowest score wins.

Now let's say the device is at image 59, the highest image is 71, and the
winning path is [61:62:68:70:71].  Normally, the device would download these
deltas and arrange for them to be applied in order on reboot.  However, before
it downloads these images, s-i filters the winning path based on the
--maximage value.  Let's say you run s-i with --maximage=69; what will
actually get downloaded and applied are images [61:62:68].  IOW, every image
greater than the --maximage is ignored, but only *after* the winning path is
calculate.

Cheers,
-Barry

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