Don't duplicate initrd and kernel files

[Paolo Pisati]

Stop duplicating kernel and initrd files in the kernel snap, use symlinks instead - as a side effect we trim +10MB from the kernel snap:

Before:

$ ls -la squashfs-root/
total 27604
drwxrwxr-x 5 flag flag 4096 mar 22 12:20 .
drwxr-xr-x 29 flag flag 4096 mar 22 12:21 ..
-rw-rw-r-- 2 flag flag 6531440 mar 22 12:20 bzImage-4.9.0+
drwxrwxr-x 36 flag flag 4096 mar 22 12:20 firmware
-rw-rw-r-- 2 flag flag 5807334 mar 22 12:20 initrd-4.9.0+.img
-rw-rw-r-- 2 flag flag 5807334 mar 22 12:20 initrd.img
-rw-rw-r-- 2 flag flag 6531440 mar 22 12:20 kernel.img
drwxrwxr-x 2 flag flag 4096 mar 22 12:20 meta
drwxrwxr-x 3 flag flag 4096 mar 22 12:20 modules
-rw-rw-r-- 1 flag flag 3559958 mar 22 12:20 System.map-4.9.0+

With this change:

$ ls -la squashfs-root/
total 15552
drwxrwxr-x 5 flag flag 4096 mar 22 12:12 .
drwxr-xr-x 29 flag flag 4096 mar 22 12:13 ..
-rw-rw-r-- 1 flag flag 6531216 mar 22 12:12 bzImage-4.9.0+
drwxrwxr-x 36 flag flag 4096 mar 22 12:12 firmware
-rw-rw-r-- 1 flag flag 5806664 mar 22 12:12 initrd-4.9.0+.img
lrwxrwxrwx 1 flag flag 17 mar 22 12:13 initrd.img -> initrd-4.9.0+.img
lrwxrwxrwx 1 flag flag 14 mar 22 12:13 kernel.img -> bzImage-4.9.0+
drwxrwxr-x 2 flag flag 4096 mar 22 12:12 meta
drwxrwxr-x 3 flag flag 4096 mar 22 12:12 modules
-rw-rw-r-- 1 flag flag 3559958 mar 22 12:12 System.map-4.9.0+

[Oliver Grawert (ogra)]

is there any need to have the versioned files at all ?

iirc we do not ever use them anyway, so they would only be relevant for users poking around inside the snap to actually see the versioning (which snap list would hopefully tell them without tinkering).

image building will only handle the unversioned variants. (in that light it might probably also be cleverer to flip around the logic and make the versioned file a symlink to the unversioned one)

[Sergio Schvezov (sergiusens)]

we are currently creating hardlinks, the PR switches that to symlinks. I am not sure what the gain is

[Sergio Schvezov (sergiusens)]

PR https://github.com/snapcore/snapcraft/pull/1207