Bug#759406: debian-cd: Merge iso images into usb drive thanks to cat
Hi,
> > There are descriptions in the web for boot media which
> > contain multiple ISOs.
> Yes, but these tools, in theory, won't work perfect with Debian Installer
> till #724931 and #759744 are fixed.
Lack of loop mounting is quite some handicap.
> "Repartition free space to store extra ISO images".
I would rather call it "Claim free space on device as new partition".
We could make a specialized little program for that.
MBR is easy to manipulate. Device size can be inquired
linux-specifically by a ioctl() or portably by binary search.
Question is what to do with GPT. (Is Live-CD prepared for EFI
isohybrid at all ?)
The GPT specs prescribe that a backup table is to be stored
at the very end of the storage device. Debian amd64 has this
backup at the end of the ISO image. This already confuses
some partition editors.
To get a neat partitioning, GPT would either have to be deleted
or the backup table has to be moved. Moving demands patching of
fields in the backup and in the main GPT. This includes computation
of new CRCs for both.
> Then you would need some of the implementation about detecting new ISOs from
> the partition directory and using them that it's already found at: #724931 .
Yes. This is a tricky part after first stages of booting.
> I personally like the
> cat idea because is very new but at the same we are saving data into an
> space that could be thought of being empty.
One could combine cat with the creation of a new partition
or with expansion of the first partition up to the end of
the storage device.
(Again, GPT will impose extra effort.)
> I ask myself what's the opinion of debian-cd people on this subject.
I assume they are waiting whether this discussion yields a
lean and stable proposal.
> > ls -l debian-7.6.0-i386-CD-1.iso
> Yes, you are right. Although fdisk -l also shows this size somewhere.
One could also inquire the size of the ISO image. :))
(Bytes 32768 + 81 to + 83 gives the number of blocks as little endian,
+ 84 to + 87 as big endian)
But actually you want to know where the next ISO will start.
With cat, this depends on the previous image file sizes.
(One could use dd seek= to put the ISOs at predefined
block addresses regardless of the size of the previous ISOs.)
> > What are the use cases where it will be of help ?
> When someone want to use CD1, CD2 and CD3 from the same usb. E.g. giving the
> usb to someone else who is offline.
I now wonder how much effort it would be to merge Debian
installation ISOs into a single ISO filesystem.
The ISO part could be easily done.
But there are files inside the ISOs which would need to be
merged or otherwise adapted.
The benefit would be to get a normal Debian ISO with no
need for any new installer features.
Have a nice day :)
Thomas
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