Fun with Fatdog
One of the forum member in Puppy Linux forum, Ted Dog, asked whether Fatdog can be modified to run with uncompressed filesystem in RAM, provided that one has enough RAM to do so. His idea is that since uncompressed Fatdog stands at around 700MB, on machines with more than 4GB it should be possible to have one giant initrd that contains uncompressed filesystem that got fully loaded into RAM and run Fatdog from there. Since there is no decompression is involved other than possible once at boot-up (if the initrd is compressed), it should run like the wind. The original post was here.There is no practical purpose of doing this (that I can see), but it sounds fun :)
There are two possible way of doing it:
1. Expand the content of the basesfs (fd64-620.sfs currently) and merge it with initrd.
2. Expand the content of the basesfs and store it into uncompressed ext2 filesystem.
In either case, it should be possible to include modifications of the original Fatdog stuff like a "remaster".
Fatdog already supports booting without any basesfs. It also supports basesfs with filesystems other than squashfs. So all that is needed is to prep the initrd.
For 1, what is needed is to get a snapshot of the running system, and do minimal modification so that it is bootable, and re-create the initrd from there.
For 2, what is needed is to create a basesfs that contains uncompressed ext2 filesystem instead of squashfs, and insert this basesfs into an existing initrd.
As it turns out - Fatdog already has the tools to help to do both: the sandbox. One runs sandbox to have a "snapshot" of the running system which one can play inside without affecting the real system. When one starts sandbox, one can choose which layers to be included in the sandbox - including the modifications already in the savefile. As it turns out, the sandbox root filesystem is also visible from outside the sandbox, in "/mnt/fakeroot" for 621 and "/mnt/sb/fakeroot" for 622 onwards. By choosing the correct layers, we can get the needed view for either 1 or 2.
From here it is straightforward.
For 1, one just needs to create the initrd from the sandbox root, after undo-ing some changes done by sandbox script, and restoring deleted links required for booting, and a minor modification to the initrd init script (/sbin/system-init).
For 2, it is even simpler - just create an empty ext2 image file, and copy over the sandbox root to that image file, again after undoing some changes done by the sandbox script. Then open up an existing initrd and overwrite the basesfs (fd64-620.sfs) there with the image file you've just created; then rebuild the script.
Fatdog's initrd currently stands at around 210MB. This "giant" initrd, when gzipped, is about 260MB. It's bigger because it is compressed with gzip instead of with xz; if one choose xz compression it will have more or less the same size. But this size difference is not important, either way the initrd will be decompressed before Fatdog starts - and the memory consumed will be the decompressed size of the initrd which is around 700MB. But then, as Ted Dog said, there will be no decompression overhead for anything, so it should run like the wind :)
I have written the details and the exact steps on how to do both 1) and 2) in the forum, so I will not repeat it here.
Method 1
Method 2
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