mirror of
https://github.com/Telecominfraproject/OpenNetworkLinux.git
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96 lines
3.5 KiB
Markdown
96 lines
3.5 KiB
Markdown
Summary
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---------
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The high-level boot process for ONL is fairly straight forward, but there is a lot detail.
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At high-level, there are three phases
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1. uBoot phase
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2. the ONL Loader phase
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3. The final ONL operating system
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Detailed Boot Process
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--------------------------
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1. uBoot is the first level boot loader: http://www.denx.de/wiki/U-Boot
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2. uBoot reads the 'nos_bootcmd' environmental variable from flash and runs the contents
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('nos' is Network Operating System)
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4. If $nos_boot_cmd returns, uBoot loads and runs ONIE (see below) to download the ONL installer and install the ONL loader
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a) The factory default $nos_boot_cmd is to a trival command that returned immediately, e.g., 'echo'
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5. In normal operation, i.e., after ONIE has been run, $nos_boot_cmd is set to load and run the ONL Loader
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6. The ONL loader boots the Linux kernel (later, the "boot kernel")
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7. The ONL loader decides which SWI to run based on the URL in the file /etc/SWI
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URL=`cat /etc/SWI`
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8. The ONL loader runs `/bin/boot $URL`
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9. The ONL loader retrieves the SWI file
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a) if the URL is remote (e.g., http://, ftp://, etc.), verify that there is a locally cached copy
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of the SWI in /mnt/flash2 or if not, download it
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b) if the URL is local, verify that the device is accessible
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c) if the URL is a Zero Touch Networking (ZTN) URL, the execute the ZTN protocol to get the SWI (see below)
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10. The ONL loader reads the 'rootfs' file out of the SWI and mounts it using overlayfs[1] (SWI contents described below)
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Partition Layout
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------------------
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Switches typically have two flash storage device: a smaller flash (e.g.,
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64MB flash) for booting and a larger, mass storage device (e.g., compact
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flash, 2+GB).
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Smaller Boot Flash:
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Partition 1: uBoot
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Partition 2: environmental variables (e.g., $nos_boot_cmd)
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Partition 3: ONIE
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Partition 4+: Free space (unused)
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Mass Storage Device:
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Partition 1: ONL loader kernel -- the format of this partition varies depending on what formats uBoot supports on the specific platform
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Partition 2: ONL Loader configuration files (mounts as "/mnt/flash" both during the loader and the main ONL phases)
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Partition 3: ONL SWitch Images (SWIs) partition (mounts as "/mnt/flash2" both during the loader and the main ONL phases)
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ONL file system layout
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-----------------------
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root@onl-powerpc:/bin# df
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Filesystem 1K-blocks Used Available Use% Mounted on
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rootfs 72040 176 71864 1% /
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devtmpfs 1024 0 1024 0% /dev
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none 72040 176 71864 1% /
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tmpfs 48028 148 47880 1% /run
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tmpfs 5120 0 5120 0% /run/lock
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/dev/sda2 71177 7 71170 1% /mnt/flash
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/dev/sda3 3791960 98172 3693788 3% /mnt/flash2
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tmpfs 96040 0 96040 0% /run/shm
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SWI
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--------
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Zip file contains:
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$ unzip -l ONL-2.0.0_ONL-OS_2015-12-12.0252-ffce159_PPC.swi
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Archive: ONL-2.0.0_ONL-OS_2015-12-12.0252-ffce159_PPC.swi
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Length Date Time Name
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--------- ---------- ----- ----
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97968128 2015-12-15 20:20 rootfs-powerpc.sqsh
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1063 2015-12-15 20:20 manifest.json
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--------- -------
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97969191 2 files
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1. 'rootfs-$ARCH' : the root file system for the running ONL
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2. 'manifest.json' : a list of supported platforms, version information about ONL and the architecture
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Footnotes
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-----------
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[1] : https://kernel.googlesource.com/pub/scm/linux/kernel/git/mszeredi/vfs/+/overlayfs.current/Documentation/filesystems/overlayfs.txt
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