bug#20909: incorrect partition size calculation

[Gena Makhomed]

On 29.06.2015 20:43, Brian C. Lane wrote:

> > incorrect partition size calculation
> >
> > # parted -v
> > parted (GNU parted) 2.3
> >
> > Model: ATA HGST HUS724040AL (scsi)
> > Disk /dev/sda: 7814037168s
> >
> > how to reproduce:
> >
> > parted -s /dev/sda mklabel gpt
> > parted -s /dev/sda -a none mkpart primary 34s 2047s
> > parted -s /dev/sda set 1 bios_grub on
> > parted -s /dev/sda mkpart primary 2048s 2099199s
> > parted -s /dev/sda set 2 raid on
> > parted -s /dev/sda mkpart primary 2099200s 102764543s
> > parted -s /dev/sda set 3 raid on
> > parted -s /dev/sda mkpart primary zfs 102764544s 7814037134s
> >
> > parted
> > (parted) unit s
> > (parted) print free
> > Model: ATA HGST HUS724040AL (scsi)
> > Disk /dev/sda: 7814037168s
> > Sector size (logical/physical): 512B/512B
> > Partition Table: gpt
> >
> > Number  Start       End          Size         File system  Name     Flags
> >   1      34s         2047s        2014s                     primary bios_grub
> >   2      2048s       2099199s     2097152s                  primary  raid
> >   3      2099200s    102764543s   100665344s                primary  raid
> >   4      102764544s  7814037134s  7711272591s               primary
> >
> > (parted)
> >
> > =======================================
> >
> > parted reports what /dev/sda4 partition has size of 7711272591s
> > but this is not true, partition size is 7711272590s:
> >
> > 7814037168 - 2014 -  2097152 - 100665344 - 34 - 34 == 7711272590
>
> You are off by 1. start and end are inclusive so the size of sda4 is:
>
> 1 + (7814037134 - 102764544) = 7711272591

yes, you are right, sorry.
7814037168 - 2014 -  2097152 - 100665344 - 33 - 33 -1 == 7711272591

2014s,  2097152s, 100665344s and 7711272591s is size of partitions,
1s size of MBR and 33s + 33s is size of two copies of GPT.

BTW, "start and end are inclusive" - IMHO is very bad decision,
because now it is not possible to partition disk using MiB units
and always need use sectors and make all calculations manually.

for example, parted -s /dev/sda mkpart primary 34s 1MiB
now use one sector from second MiB and next partition
will be created as unaligned.

if use common scheme as in java - start index inclusive
and end index exclusive, - disk partitioning
will be very easy and obvious:

parted -s /dev/sda mkpart primary 34s 1MiB
parted -s /dev/sda mkpart primary 1MiB 1025MiB
parted -s /dev/sda mkpart primary 1025MiB 50178MiB
parted -s /dev/sda mkpart primary 50178MiB -- -34s

1-MiB alignment boundary recommended
for all GPT partitions except bios_grub one,
which contains core.img for read-only access:
https://en.wikipedia.org/wiki/BIOS_boot_partition

--
Best regards,
 Gena