Module Name: src
Committed By: mlelstv
Date: Sat Apr 25 14:05:43 UTC 2015
Modified Files:
src/share/man/man8/man8.x86: boot.8
Log Message:
Explain how the kernel determines the root filesystem from information
passed by the bootloader.
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/share/man/man8/man8.x86/boot.8
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/share/man/man8/man8.x86/boot.8
diff -u src/share/man/man8/man8.x86/boot.8:1.4 src/share/man/man8/man8.x86/boot.8:1.5
--- src/share/man/man8/man8.x86/boot.8:1.4 Sat Aug 16 12:30:12 2014
+++ src/share/man/man8/man8.x86/boot.8 Sat Apr 25 14:05:43 2015
@@ -1,4 +1,4 @@
-.\" $NetBSD: boot.8,v 1.4 2014/08/16 12:30:12 apb Exp $
+.\" $NetBSD: boot.8,v 1.5 2015/04/25 14:05:43 mlelstv Exp $
.\"
.\" Copyright (c) 1991, 1993
.\" The Regents of the University of California. All rights reserved.
@@ -624,6 +624,55 @@ In an emergency, the bootstrap methods d
installation notes for the x86 architectures
can be used to boot from floppy or other media,
or over the network.
+.Ss Locating the root filesystem
+The kernel uses information from the bootloader to locate the
+filesystem to mount as root. There are three methods:
+.Bl -tag -width 04n -offset 04n
+.It Ic BTINFO_ROOTDEVICE Va from
+.Xr boot.cfg 5
+or multiboot.
+The bootloader passes the root device name as driver,unit and
+partition (like sd0a). This will be automatically substituted
+by a
+.Xr dk 4
+wedge if one is discovered.
+.Pp
+The bootloader passes a wedge name as "wedge:" followed by the name.
+The kernel will search for a
+.Xr dk 4
+device with that name.
+.It Ic BTINFO_BOOTWEDGE Va determined by bootblock
+The bootloader passes start offset and length of a hard disk partition
+and a offset, size and hash of a "boot area". Then kernel searches
+all disks and wedges for a block sequence at that offset with a
+matching hash. If one is found, the kernel will look for a wedge
+on that device at the same offset.
+.Pp
+An additional partition number is provided if the bootloader also
+passed a BTINFO_BOOTDISK record. This (or partition 'a') will be used
+by the kernel as a fallback if there is no matching wedge.
+.It Ic BTINFO_BOOTDISK Va determined by bootblock
+This uses the device number passed by the BIOS that
+distinguishes between floppy, hard drive and CD-ROM boot.
+.Bl -tag -width xxx
+.It Ic Floppy
+The kernel searches for the
+.Xr fd 4
+device with the correct unit, the partition number is used
+to select a specific disk format. See
+.Xr fd 4 for details.
+.It Ic Hard drive
+The bootloader passed a partition number and disklabel
+data (offset, type, checksum, packname). The kernel searches
+all disks for a matching disklabel. If one is found, the
+kernel will use that device and partition number.
+.It Ic CDROM
+The BIOS does not distinguish between multiple CD devices.
+The kernel searches for the first
+.Xr cd 4
+device. So you can only boot from unit 0.
+.El
+.El
.Sh FILES
.Bl -tag -width /usr/mdec/bootxx_fstype -compact
.It Pa /boot
@@ -647,6 +696,7 @@ partition by
.Xr ddb 4 ,
.Xr pciback 4 ,
.Xr userconf 4 ,
+.Xr fd 4 ,
.Xr boot.cfg 5 ,
.Xr boot_console 8 ,
.Xr dosboot 8 ,
