Closed mirschkyn closed 2 years ago
That sector is the EBR (https://en.wikipedia.org/wiki/Extended_boot_record). It's the first sector in the extended partition so the logical partition will start at least on sector after the extended partition. The offset may be larger depending on the alignment of the partition. Each partition has its align
property. If that's not set, then the align
from the hdimage section is used.
Ok. But it looks strange. More like an offset than an alignment?
/dev/loop33p4 16384 15859708 15843325 7,6G f W95 Ext'd (LBA) /dev/loop33p5 16385 540672 524288 256M da Non-FS data /dev/loop33p6 540674 1064961 524288 256M da Non-FS data /dev/loop33p7 1064963 1589250 524288 256M da Non-FS data
Here. p4 is at 16384, occupies 1. p5 starts at +1 p6 starts at +2, even. p7 starts at +2, uneven, despite sizes being even.
I have no explicit alignment anywhere in the config to genimage. So expected behavior would be align to something even, and if not aligning, then not add 2? But rather step to the next sector? Am I reading this wrong?
Your reading this wrong: 540672 is the last sector of p5, 540673 is the EBR and 540674 is the first sector of p6. So there is no gap. The default alignment is on sector.
Ah. Yes, the EBR is a linked list, with an entry in front of every logical partition, right? That explains the sectors. Thanks for filling in the gaps!
Created a hdimage with genimage. The extended partition seems to occupy a physical sector, by starting the next partition at sector + 1 (fdisk output). I can't find any information regarding this.
/dev/loop33p4 16384 16384004 16367621 7,8G f W95 Ext'd (LBA) /dev/loop33p5 16385 540672 524288 256M da Non-FS data
edit: The question is partly about the alignment post EBR in relation to the EBR size.