Updated documentation about MBR

xorriso/xorriso.texi

@@ -505,25 +505,20 @@ Most bootable GNU/Linux CDs are equipped with ISOLINUX or GRUB boot images.
 xorriso is able to create or maintain an El Torito object which makes such
 an image bootable. For details see option -boot_image.
 @*
+@cindex MBR, _definiton
 It is possible to make ISO images bootable from USB stick or other
-hard-disk-like media by -boot_image argument system_area= .
+hard-disk-like media by -boot_image argument system_area= . This installs
+a Master Boot Record which may get adjusted according to the needs
+of GRUB resp. ISOLINUX.
+An @strong{MBR} contains boot code and a partition table. It does not hamper
+CDROM booting. The new MBR of a follow-up session can get in effect
+only on overwriteable media.
 @*
 Emulation -as mkisofs supports the example options out of the ISOLINUX wiki.
 It also supports the options used in GRUB script grub-mkrescue.
 @*
 The support for other boot image types is sparse.
 @*
-@c
-@c >>> isohybrid MBR generation has been disabled on request
-@c >>> of its inventor H. Peter Anvin on 31 Mar 2010
-@c
-@c An MBR is generated together with the El Torito boot record if the
-@c boot image bears the isohybrid signature of ISOLINUX 3.72 or later.
-@c It will occupy the first 512 bytes of the emerging ISO image and
-@c enable booting from media which appear as hard disk rather than
-@c as CDROM. An MBR does not hamper CDROM booting. The MBR of a
-@c follow-up session can get in effect only on overwriteable media.
-@c
 @c man .PP
 @sp 1
 @cindex ACL, _definiton
@@ -2700,36 +2695,40 @@ is given by "any" "bin_path=". "boot_info_table=off" disables patching.
 "patch" applies boot info table patching if an existing boot image gets copied
 to a new location.
 @*
+@cindex System area, _definiton
+@cindex MBR, set, -boot_image system_area=
 "system_area="disk_path copies at most 32768 bytes from the given disk file to
 the very start of the ISO image.
 This System Area is reserved for system dependent boot software, e.g. an MBR
 which can be used to boot from USB stick or hard disk.
 @*
-Special disk_path "/dev/zero" causes 32k of NUL-bytes.
-Use this to discard an MBR which eventually was loaded with the ISO image.
-@*
 Other than a El Torito boot image, the file disk_path needs not to be added
 to the ISO image.
 @*
 -boot_image isolinux system_area= implies "partition_table=on".
 @*
+@cindex Partition table, _definiton
 "partition_table=on" causes a simple partition table to be written into bytes
 446 to 511 of the System Area.
 @*
 With type "isolinux" it shows a partition that begins at byte 0 and it causes
-the boot image LBA to be written into the MBR. This works only if also
-"system_area=" and "bin_path=" or "dir=" is given.
+the boot image LBA to be written into the MBR. For the first session this
+works only if also "system_area=" and "bin_path=" or "dir=" is given.
 @*
 With types "any" and "grub" it shows a single
 partiton which starts at byte 512 and ends where the ISO image ends.
 This works with or without system_area= or boot image.
 @*
-@c
-@c Bootspec "isohybrid=off" disables MBR generation, "isohybrid=on"
-@c prevents the write session if not the isohybrid signature is found
-@c in the bin_path file. Default is "isohybrid=auto" which silently
-@c omits the MBR if the signature is missing. 
-@c 
+In follow-up sessions the existing System Area is preserved by default.
+If types "isolinux" or "grub" are set to "patch", then "partition_table=on"
+is activated without new boot image.
+In this case the existing System Area gets checked whether it bears addresses
+and sizes as if it had been processed by "partition_table=on". If so,
+then those parameters get updated when the new System Area is written.
+@*
+Special "system_area=/dev/zero" causes 32k of NUL-bytes.
+Use this to discard an MBR which eventually was loaded with the ISO image.
+@*
 @end table
 @c man .TP
 @c man .B Character sets:
@@ -3765,7 +3764,7 @@ same name and hardcoded argument "on", e.g. -acl "on".
 Explicit arguments are expected by @minus{}@minus{}stdio_sync
 and @minus{}@minus{}scdbackup_tag.
 @*
-@minus{}@minus{}sort-weight gets as argument a number and an iso_rr_path.
+@minus{}@minus{}sort-weight gets as arguments a number and an iso_rr_path.
 The number becomes the LBA sorting weight of regular file iso_rr_path or
 of all regular files underneath directory iso_rr_path.
 (See -find -exec sort_weight).
@@ -3779,8 +3778,6 @@ For MBR bootable ISOLINUX images there is -isohybrid-mbr FILE, where
 FILE is one of the Syslinux files mbr/isohdp[fp]x*.bin . Use this
 instead of -G to apply the effect of -boot_image isolinux partition_table=on.
 @*
-@c Quite special is isolinux_mbr= (see -boot_image isolinux isohybrid=).
-@c @*
 Personalites "@strong{xorrisofs}", "@strong{genisoimage}",
 and "@strong{genisofs}" are aliases for "mkisofs".
 @*