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Updated libisoburn doc/*.wiki files by current publicly shown files

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This commit is contained in:
Thomas Schmitt
2017-09-06 14:42:21 +02:00
parent 047b8db7ac
commit 650c015c5b
3 changed files with 596 additions and 585 deletions
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doc/partition_offset.wiki
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@@ -6,7 +6,7 @@ Thus it marks a small part of the device as unclaimed by partitions and
available for storing boot loader code.
Nevertheless the USB stick is mountable via its overall device file as well as
via the partition device file. E.g. on GNU/Linux: /dev/sdb and /dev/sdb1.
via the partition device file. E.g. on GNU/Linux: `/dev/sdb` and `/dev/sdb1`.
This is achieved by two distinct sets of meta-data which refer to the same
file content.
@@ -19,21 +19,15 @@ extend the unclaimed area into vital blocks of the ISO image.
--------------------------------------------------------------------------
Meanwhile Debian
[http://cdimage.debian.org/cdimage/daily-builds/daily/current/ daily]
and [http://cdimage.debian.org/cdimage/weekly-builds/ weekly] builds make
use of this feature with their bootable ISO images for i386. E.g.
[http://cdimage.debian.org/cdimage/daily-builds/daily/current/i386/iso-cd/debian-testing-i386-netinst.iso debian-testing-i386-netinst.iso].
According to a
[http://syslinux.zytor.com/archives/2011-March/016201.html thread of march 2011]
[thread of march 2011](http://www.syslinux.org/archives/2011-March/016527.html)
on Syslinux mailing list this enabled booting of a Kontron CG2100 server
from USB stick, which otherwise failed.
Regrettably the feature seems to prevent mounting of ISO 9660 images on
Apple "Snow Leopard" systems.
At least this is the outcome of a
[http://lists.debian.org/debian-cd/2011/04/msg00029.html debian-cd thread of april 2011].
[debian-cd thread of april 2011](http://lists.debian.org/debian-cd/2011/04/msg00029.html).
--------------------------------------------------------------------------
@@ -46,33 +40,33 @@ Overview:
The test image was derived from one year old RIPLinux-9.3-non-X.iso which
has an isohybrid MBR. Syslinux version seems to be 3.82. That MBR and the file
tree from the mounted RIPLinux image was used to build a new ISO image
with 16 * 2kB partition offset. Isohybrid MBR patching was done by xorriso.
with 16 \* 2kB partition offset. Isohybrid MBR patching was done by xorriso.
Details:
The first 32 kB of an ISO 9660 image are called System Area and may host any
byte pattern. The first 512 bytes of RIPLinux-9.3-non-X.iso contain the
isohybrid capable MBR, which will be re-used in this example.
{{{
```
dd if=RIPLinux-9.3-non-X.iso bs=512 count=1 of=RIPLinux-9.3-non-X.mbr
}}}
```
Normally the isohybrid MBR is provided by the Syslinux
installation under the name isohdp[fp]x*.bin .
E.g. /usr/lib/syslinux/isohdpfx.bin
installation under the name `isohdp[fp]x*.bin` .
E.g. `/usr/lib/syslinux/isohdpfx.bin`
The files of the image are made accessible for reading
{{{
```
mount -o loop RIPLinux-9.3-non-X.iso /mnt
}}}
```
A new ISO image gets composed. The first three lines of arguments are taken
from the prescriptions of ISOLINUX wiki and adapted to the names used in
RIPLinux-9.3-non-X.iso.
Option -isohybrid-mbr imports the copied MBR and patches it
Option `-isohybrid-mbr` imports the copied MBR and patches it
according to rules published by hpa on Syslinux mailing list.
Option -partition_offset 16 causes the first partition to start at 2 kB block
Option `-partition_offset 16` causes the first partition to start at 2 kB block
number 16. It also prepares the image to be mountable by this partition, too.
{{{
```
xorriso -as mkisofs \
-o new_image.iso \
-b boot/isolinux/isolinux.bin -c boot/boot.cat \
@@ -80,80 +74,80 @@ number 16. It also prepares the image to be mountable by this partition, too.
-isohybrid-mbr RIPLinux-9.3-non-X.mbr \
-partition_offset 16 \
/mnt
}}}
```
The image was copied onto a USB stick
{{{
```
dd if=new_image.iso of=/dev/sdc
}}}
```
and plugged into a Debian system.
{{{
```
fdisk -lu /dev/sdb
}}}
```
yields
{{{
```
Device Boot Start End Blocks Id System
/dev/sdb1 * 64 120831 60384 17 Hidden HPFS/NTFS
}}}
```
I can mount /dev/sdb and /dev/sdb1 alike:
{{{
I can mount `/dev/sdb` and `/dev/sdb1` alike:
```
mount /dev/sdb1 /mnt1
mount -o loop /dev/sdb /mnt
}}}
-o loop avoids failure with "mount: /dev/sdb already mounted or /mnt busy".
```
`-o loop` avoids failure with "mount: /dev/sdb already mounted or /mnt busy".
A comparison by
{{{
```
diff -r /mnt /mnt1
}}}
```
reports no difference.
Human readable files look ok.
Test-reading all content by
{{{
```
tar cf - /mnt | wc
}}}
```
yields a reasonable byte count of 60743680 and no errors.
The machine boots RIPLinux from this USB stick with no visible problems.
It can then mount /dev/sdb as well as /dev/sdb1.
It can then mount `/dev/sdb` as well as `/dev/sdb1`.
The ISO image boots from CD too.
Mounting the partition can be simulated with an image file on hard disk by
cutting off the first partition_offset blocks of 2 KB:
{{{
```
dd if=new_image.iso of=partition_image.iso bs=2048 skip=16
mount -o loop partition_image.iso /mnt1
}}}
```
--------------------------------------------------------------------------
Another test was made with GRUB 2 by downloading
{{{
```
bzr branch http://bzr.savannah.gnu.org/r/grub/trunk/grub
}}}
```
Before building GRUB 2, the file
{{{
```
util/grub-mkrescue.in
}}}
```
was edited to replace in the options of the xorriso command:
{{{
```
--protective-msdos-label
}}}
```
by
{{{
```
-partition_offset 16 -no-pad
}}}
```
Then GRUB 2 was built and installed.
The resulting image from
{{{
```
./grub-mkrescue -o image.iso
}}}
```
was put onto USB stick. It passed the same tests on Debian
as above RIPLinux example. It boots to a GRUB prompt.
Due to option -no-pad the image is about 250 kB smaller than
the image produced by original grub-mkrescue. Else it would have grown by
Due to option `-no-pad` the image is about 250 kB smaller than
the image produced by original `grub-mkrescue`. Else it would have grown by
about 50 kB.
Unpadded ISO images are safe except for burning on CD in TAO mode.
@@ -163,11 +157,11 @@ require padding by 300 kB.
Burning on DVD or BD needs no such caution. Neither does copying
on USB stick or hard disk.
Program fdisk will complain about "different physical/logical" addresses.
Program `fdisk` will complain about "different physical/logical" addresses.
This can be silenced by adding option
{{{
```
-partition_cyl_align on
}}}
```
at the cost of image padding up to the next full MB.
E.g. by 402 kB to 2 MB.
@@ -187,7 +181,7 @@ preparations.
Application:
The partition offset feature can be controlled by libisofs API calls
{{{
```
int iso_write_opts_set_part_offset(IsoWriteOpts *opts,
uint32_t block_offset_2k,
int secs_512_per_head,
@@ -195,9 +189,9 @@ int iso_write_opts_set_part_offset(IsoWriteOpts *opts,
int iso_write_opts_set_system_area(IsoWriteOpts *opts, char data[32768],
int options, int flag);
}}}
```
or by libisoburn calls
{{{
```
int isoburn_igopt_set_part_offset(struct isoburn_imgen_opts *opts,
uint32_t block_offset_2k,
int secs_512_per_head, int heads_per_cyl);
@@ -211,9 +205,9 @@ int isoburn_igopt_set_system_area(struct isoburn_imgen_opts *o,
int isoburn_igopt_get_system_area(struct isoburn_imgen_opts *o,
char data[32768], int *options);
}}}
```
or by xorriso options
{{{
```
-boot_image any partition_offset=(2kb_block_adr)
-boot_image any partition_sec_hd=(number)
-boot_image any partition_hd_cyl=(number)
@@ -223,7 +217,7 @@ or by xorriso options
-partition_hd_cyl (number) \
-partition_sec_hd (number) \
-partition_cyl_align (on|auto|off) ...
}}}
```
As stated above, an offset larger than 16 would expose vital parts of the
ISO image as unclaimed space. Values smaller than 16 are not accepted.