#!/bin/sh
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# This scripts makes a minimal bootable SD card image for the Chromebook.
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# The resulting file is called bootsd.img. It should be written directly
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# to the card:
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#
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# SD=/dev/mmcblk1 # check your device name!
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# dd if=output/images/bootsd.img of=$SD
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#
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# The partitions are created just large enough to hold the kernel and
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# the rootfs image. Most of the card will be empty, and the secondary
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# GPT will not be in its proper location.
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# cgpt does not create protective MBR, and the kernel refuses to read
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# GPT unless there's some kind of MBR in sector 0. So we need parted
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# to write that single sector before doing anything with the GPT.
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cgpt=$HOST_DIR/bin/cgpt
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parted=$HOST_DIR/sbin/parted
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kernel=$BINARIES_DIR/uImage.kpart
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rootfs=$BINARIES_DIR/rootfs.ext2
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run() { echo "$@"; "$@"; }
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die() { echo "$@" >&2; exit 1; }
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test -f $kernel || die "No kernel image found"
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test -f $rootfs || die "No rootfs image found"
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test -x $cgpt || die "cgpt not found (host-vboot-utils have not been built?)"
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# True file sizes in bytes
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kernelsize=`stat -t $kernel | cut -d\ -f2`
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rootfssize=`stat -t $rootfs | cut -d\ -f2`
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# The card is partitioned in sectors of 8KB.
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# 4 sectors are reserved for MBR+GPT. Their actual size turns out
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# to be 33 512-blocks which is just over 2 sectors, but we align
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# it to a nice round number.
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sec=8192
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kernelsec=$(((kernelsize+8191)>>13))
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rootfssec=$(((rootfssize+8191)>>13))
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headersec=4
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# There is also a copy of MBR+GPT at the end of the image.
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# It's going to be useless but both tools assume it's there.
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imagesec=$((2*headersec+kernelsec+rootfssec))
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bootsd="$BINARIES_DIR/bootsd.img"
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run dd bs=$sec count=$imagesec if=/dev/zero of=$bootsd
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# cgpt needs offsets and sizes in 512-blocks.
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block=512
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kernelstart=$((headersec<<4))
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kernelblocks=$((kernelsec<<4))
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rootfsblocks=$((rootfssec<<4))
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rootfsstart=$((kernelstart+kernelblocks))
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# This command initializes both GPT and MBR
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run $parted -s $bootsd mklabel gpt
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# The kernel partition must be marked as bootable, that's why -S -T -P
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run $cgpt add -i 1 -b $kernelstart -s $kernelblocks \
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-t kernel -l kernel \
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-S 1 -T 1 -P 10 $bootsd
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# It does not really matter where the rootfs partition is located as long
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# as the kernel can find it.
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# However, if anything is changed here, kernel.args must be updated as well.
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run $cgpt add -i 2 -b $rootfsstart -s $rootfsblocks \
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-t data -l rootfs $bootsd
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run dd bs=$block if=$kernel of=$bootsd seek=$kernelstart
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run dd bs=$block if=$rootfs of=$bootsd seek=$rootfsstart
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