[parted-devel] [PATCH] libparted: Add support for MBR id and GPT GUID of UDF filesystem

[Phillip Susi]

On 8/24/2018 3:29 AM, Pali Rohár wrote:
> No, offset where VRS starts is fixed to 32kB, independently of block
> size.

I thought it was 32kb + x * block size, where x is 0..63?

> For UDF block size 512 - 2048, size of VSD blocks in VRS is always 2048.

Size, yes.  I'm talking about the location.  It can be in blocks 0..63,
so it's exact offset depends on the block size does it not?  Except of
course for block zero since zero * any block size is still zero.

> Yes, probe for VSD with 2048 VSD length, and check for AVDP with UDF
> block size 512, 1024 and 2048.

Again, there is a difference between the length of the VRS itself, and
where it is located.  For a block size of 512, the VRS could be located
in block 5, which would put it between bytes 2560 and 2560+2048-1.

>> So you are trying to check only the most common anchor position first
>> for each detected block size so that if one or two vrs checks were false
>> positives, you don't waste as much time checking the other 3 anchor
>> locations?
> 
> No, I'm checking for all possible location. But for "most common"
> location (AVDP at 256) is checked as the first. Later (in the last
> loop) are checked other AVDP locations.

Yes, that's what I said.

> Why not? For valid UDF filesystem we finish detection as early as
> possible.

Because 99% of the time you won't be looking at a valid UDF filesystem
so 99% of the time, this optimization isn't helping.

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