Diff for /wikisrc/kernel_debugging_with_qemu.mdwn between versions 1.2 and 1.4

version 1.2, 2010/04/21 21:22:01 version 1.4, 2011/03/31 09:00:49
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 Virtual machines are a convenient way to test, debug or even audit different systems on one single host. This is particularly helpful when you need to set up a machine for which you do not necessarily have the hardware, or the access, in a very cheap way, without risking breaking your day-to-day system.  Virtual machines are a convenient way to test, debug or even audit different systems on one single host. This is particularly helpful when you need to set up a machine for which you do not necessarily have the hardware, or the access, in a very cheap way, without risking breaking your day-to-day system.
   
 This tutorial show the different steps required to set up a raw disk image like the one used by QEMU. It deals with two different point of views:  This tutorial show the different steps required to set up a raw disk image like the one used by QEMU. It deals with two different point of views:
   
 * the host, which is the machine and OS hosting the different VMs.  * the host, which is the machine and OS hosting the different VMs.
 * the guest(s), representing the different systems emulated/hosted on the host, through QEMU.  * the guest(s), representing the different systems emulated/hosted on the host, through QEMU.
   
Line 12  This tutorial show the different steps r Line 13  This tutorial show the different steps r
   
 To start our VM, we need some disk space to provide an emulated hard drive. For QEMU, by default, this is done through raw disk images. Therefore, the first step will be the creation of a disk image file. Here, we create a 2GB file, filled with zeros:  To start our VM, we need some disk space to provide an emulated hard drive. For QEMU, by default, this is done through raw disk images. Therefore, the first step will be the creation of a disk image file. Here, we create a 2GB file, filled with zeros:
   
 $    dd if=/dev/null of=netbsd-guest.img bs=1m count=2000  [[!template  id=programlisting text="""
   $ dd if=/dev/zero of=netbsd-guest.img bs=1m count=2000
   """]]
   
 /!\ if you want to mount the file image from within the host later through [[!template id=man name="vnconfig" section="8"]], it is recommended to use [[!template id=man name="dd" section="1"]] and not the *qemu-img* tool, as [[!template id=man name="vnd" section="4"]] does not support sparse disk image yet.  /!\ if you want to mount the file image from within the host later through [[!template id=man name="vnconfig" section="8"]], it is recommended to use [[!template id=man name="dd" section="1"]] and not the *qemu-img* tool, as [[!template id=man name="vnd" section="4"]] does not support sparse disk image yet.
   
 Now that the disk image file is ready, we will need to install our system inside.  Now that the disk image file is ready, we will need to install our system inside.
   
 ## Copy bootloader and create disklabel  ## Preparing the MBR, labels, and first stage boot loader
   
   Mount the image file as a [[!template id=man name="vnd" section="4"]] device. This will allow manipulating the image file just like a regular hard disk drive:
   
 ## Mount the filesystem  [[!template  id=programlisting text="""
   # vnconfig -c vnd0 netbsd-guest.img
   """]]
   
   ### Creating MBR
   
   Setup the MBR; it musts contain the NetBSD partition. This will be done interactively via [[!template id=man name="fdisk" section="8"]]:
   
   [[!template  id=programlisting text="""
   # fdisk -u -a -0 /dev/rvnd0
   Disk: /dev/rvnd0d
   [...]
   Do you want to change our idea of what BIOS thinks? [n] *n*
   
   Partition 0:
   <UNUSED>
   The data for partition 0 is:
   <UNUSED>
   sysid: [0..255 default: 169] *press enter*
   start: [0..255dcyl default: 63, 0dcyl, 0MB] *press enter*
   size: [0..255dcyl default: 4095937, 255dcyl, 2000MB] *press enter*
   bootmenu: [] *press enter*
   Do you want to change the active partition? [n] *y*
   Choosing 4 will make no partition active.
   active partition: [0..4 default: 0] *press enter*
   Are you happy with this choice? [n] *y*
   We haven't written the MBR back to disk yet.  This is your last chance.
   Partition table:
   0: NetBSD (sysid 169)
       start 63, size 4095937 (2000 MB, Cyls 0-254/245/55), Active
           PBR is not bootable: All bytes are identical (0x00)
   1: <UNUSED>
   2: <UNUSED>
   3: <UNUSED>
   Bootselector disabled.
   First active partition: 0
   Should we write new partition table? [n] *y*
   """]]
   
   ### Editing labels
   
   Edit the labels, with [[!template id=man name="disklabel" section="8"]]. The example below will create:
   
   * label **a**, approximately 1.5GiB long -- will contain the future FFS / partition
   * label **b**, 512MiB swap.
   
   [[!template  id=programlisting text="""
   # disklabel -e -I /dev/rvnd0
   [...]
   4 partitions:
   #        size    offset     fstype [fsize bsize cpg/sgs]
    a:   3047361        63     4.2BSD      0     0     0  # (Cyl.      0*-   1487)
    b:   1048576   3047424       swap                     # (Cyl.   1488 -   1999)
    d:   4096000         0     unused      0     0        # (Cyl.      0 -   1999)
   """]]
   
   ### Copying first stage boot loader
   
   Lastly, we have to install the first stage boot loader, the one that will be able to read the second stage boot loader, which will reside in partition **a**. Use [[!template id=man name="installboot" section="8"]]:
   
   [[!template  id=programlisting text="""
   # installboot /dev/rvnd0a /usr/mdec/bootxx_ffsv2
   """]]
   
   ## Format and mount the filesystem
   
   With [[!template id=man name="newfs" section="8"]], format label **a** in FFSv2:
   
   [[!template  id=programlisting text="""
   # newfs -O2 /dev/rvnd0a
   /dev/rvnd0a: 1488.0MB (3047360 sectors) block size 16384, fragment size 2048
           using 9 cylinder groups of 165.34MB, 10582 blks, 20544 inodes.
   super-block backups (for fsck_ffs -b #) at:
   160, 338784, 677408, 1016032, 1354656, 1693280, 2031904, 2370528, 2709152,
   """]]
   
   then [[!template id=man name="mount" section="8"]] it:
   
   [[!template  id=programlisting text="""
   # mkdir /tmp/netbsd-guest
   # mount /dev/vnd0a /tmp/netbsd-guest
   """]]
   
 # Installing the system  # Installing the system
   
Line 32  Now that the disk image file is ready, w Line 118  Now that the disk image file is ready, w
   
 # Starting-up the VM  # Starting-up the VM
   
   # Debugging
   
 # Convenient scripts  # Convenient scripts

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