Uboot on FAT partition

Phishfry

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I am attempting to learn Crochet and I am going though the manuals and I have a simple nagging question:

Why does Uboot use a FAT partitioning scheme?

It seems odd to a Windows>XP hater. Linux and BSD using FAT...

Looking here I guess maybe the projects age has something to do with it?
http://www.denx.de/wiki/U-Bootdoc/Presentation

Supported Filesystems (read-only):

  • FAT
  • Reiser
  • JFFS2
 

SirDice

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No, it's simply because a Raspberry Pi and several other boards can only boot from FAT. Also note that UEFI systems boot from a FAT partition too.
 

Atsuri

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I think I'm still a bit of a layman in terms of file systems, but is not perhaps that FAT has a smaller footprint and as a file system occupies less HDD space on the partition for file system related tools?

That's how I would reason the use of FAT for both UEFI and Raspberry Pi boot partitions.
 

SirDice

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I think I'm still a bit of a layman in terms of file systems, but is not perhaps that FAT has a smaller footprint and as a file system occupies less HDD space on the partition for file system related tools?
Very much possible. I've tried looking up why they choose FAT but was unable to find anything. Possibly because it's a fairly simple layout and is therefor easily implemented in firmware. And I think it's also one of the most compatible filesystems, most operating systems are capable of handling it.

If anybody knows the reasoning behind the choice I'd be very interested to hear it :)
 

ondra_knezour

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SirDice you make me really curious about such reasoning, however I also didn't find anything factual, only quick overview of the UEFI "evolution" at http://www.uefi.org/sites/default/files/resources/A_Tale_of_Two_Standards_0.pdf

And being strict, one have to say, that the chosen format is not exactly FATxx, but EFI system partition
“The file system supported by the Extensible Firmware Interface is based on the FAT file system. EFI defines a specific version of FAT that is explicitly documented and testable. Conformance to the EFI specification and its associate reference documents is the only definition of FAT that needs to be implemented to support EFI. To differentiate the EFI file system from pure FAT, a new partition file system type has been defined.”
Finally, nice link :) https://www.happyassassin.net/2014/01/25/uefi-boot-how-does-that-actually-work-then/
 

Crivens

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When searching for "what is this FATxx really?", rhe closest thing to an actual spec I came to was "if the checkdisk of W2K likes it, it's OK". And that was from "upstream" there. So, finally, something documented - even if it is not the real thing.
 
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Phishfry

Phishfry

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I felt dumb asking the question but I do like to know how things work.
 
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