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Hello,
There is something that i cant understand.

Why all numerical data in mkfs.c XV6 file system image creator, are converted from big<-->little endian and vice versa.

example :
in the superblock :


then :


I have try to figure out why but it is pretty closed subject.

I hope this question relevant.

It converts between host-endian and little-endian. On a big-endian host, it converts between big-endian and little-endian. On a little-endian host, the conversion doesn't do anything.

It does that because mkfs needs to be able to run on both big-endian and little-endian CPUs, but the filesystem is always little-endian.

like that ?

Assuming 0x12345678:

On a Big Endian system:
Original x in memory: [12][34][56][78]
After xint(), y in memory: [78][56][34][12] (bytes are reversed)
This will appear as a change when viewing memory.

On a Little Endian system:
Original x in memory: [78][56][34][12]
After xint(), y in memory: [78][56][34][12] (bytes stay in same order)
This will appear as no change when viewing memory.


And so the disk image is in little endian... when a big endian proc have to use it, it should reverse all numerical data every times ?

Yep, you've got it.


Yes, but xv6 only runs on little-endian CPUs.