Updated partition offset wiki about cylinder alignment

master
Thomas Schmitt 12 years ago
parent 2fdc41a357
commit 88f37f2e93

@ -131,7 +131,7 @@ was edited to replace in the options of the xorriso command:
}}}
by
{{{
-partition_offset 16 -no-pad --no-emul-toc
-partition_offset 16 -no-pad
}}}
Then GRUB 2 was built and installed.
@ -142,10 +142,24 @@ The resulting image from
was put onto USB stick. It passed the same tests on Debian
as above RIPLinux example. It boots to a GRUB prompt.
Due to options -no-pad --no-emul-toc the image is about 300 kB smaller than
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 130 kB. The mkisofs emulation of newer versions of xorriso has
--no-emul-toc as default. Thus the overhead would only be about 50 kB.
about 50 kB.
Unpadded ISO images are safe except for burning on CD in TAO mode.
In this case problems may occur with reading the last few data blocks.
So when burning onto CD make sure to require SAO mode and/or to
require padding by 300 KiB.
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.
This can be silenced by adding option
{{{
-partition_cyl_align on
}}}
at the cost of image padding up to the next full MiB.
E.g. by 402 KiB to 2 MiB.
--------------------------------------------------------------------------
@ -162,12 +176,15 @@ preparations.
Application:
The partition offset feature can be controlled by libisofs API call
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,
int heads_per_cyl);
int iso_write_opts_set_system_area(IsoWriteOpts *opts, char data[32768],
int options, int flag);
}}}
resp. by libisoburn calls
{{{
@ -178,13 +195,24 @@ int isoburn_igopt_set_part_offset(struct isoburn_imgen_opts *opts,
int isoburn_igopt_get_part_offset(struct isoburn_imgen_opts *opts,
uint32_t *block_offset_2k,
int *secs_512_per_head, int *heads_per_cyl);
int isoburn_igopt_set_system_area(struct isoburn_imgen_opts *o,
char data[32768], int options);
int isoburn_igopt_get_system_area(struct isoburn_imgen_opts *o,
char data[32768], int *options);
}}}
resp. 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)
-as mkisofs ... -partition_offset (2kb_block_adr) ...
-boot_image any partition_cyl_align(on|auto|off)
-as mkisofs ... -partition_offset (2kb_block_adr) \
-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

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