Attachment 7446 Details for Bug 34481 – comments.patch

[patch] comments.patch

comments.patch (text/plain), 3.01 KB, created by Leonid Krivoshein on 2018-03-23 01:06:22 MSK

(hide)

Description:

Filename:

MIME Type:

Creator: Leonid Krivoshein

Created: 2018-03-23 01:06:22 MSK

Size: 3.01 KB

patch

obsolete

>commit 9ff35b028aa13ebe40ab84158d22faa85a5bf20d
>Author: Leonid Krivoshein <klark@altlinux.org>
>Date:   Fri Mar 23 00:58:26 2018 +0300
>
>    Add description for MBR/GPT and boot flag detection
>
>diff --git a/rpm/extlinux-config b/rpm/extlinux-config
>index db90250..3562736 100755
>--- a/rpm/extlinux-config
>+++ b/rpm/extlinux-config
>@@ -39,12 +39,18 @@ print_version() {
> 	exit
> }
> 
>+# Read 32-bit little-endian from GPT header and output its as decimal number.
>+# GPT header begins in the second sector of the disk. $1 is offset.
>+#
> read_gpt() {
> 	local offset=$(($sector_size + $1))
> 	dd if="$dev" bs=1 skip=$offset count=4 2>/dev/null |
> 		hexdump '-e"%u"'
> }
> 
>+# Read single byte from partition table element and output its as decimal number.
>+# GPT partition table begins in the third sector of the disk. $1 is offset.
>+#
> read_entry() {
> 	local offset=$(($sector_size * 2 + $1))
> 	local x="$(dd if="$dev" bs=1 skip=$offset count=1 2>/dev/null)"
>@@ -106,13 +112,24 @@ verbose "Device name: $dev"
> verbose "Partition number: $partition"
> verbose "Sector size: $sector_size"
> 
>+#
>+# First, 2-bytes MBR-signature at address 510 (end of the first sector) is read.
>+# It should be read as 0x55, 0xAA.
>+# https://en.wikipedia.org/wiki/Master_boot_record#Sector_layout
>+#
> magic="$(dd if="$dev" bs=2 skip=255 count=1 2>/dev/null | base64)"
> [ "$magic" = "Vao=" ] ||
> 	fatal "Unknown partition table"
> 
>-magic="$(dd if="$dev" bs=8 skip=64 count=1 2>/dev/null)"
>+#
>+# Then 8-bytes GPT-signature "EFI PART" is checked at the beginning of the second
>+# sector of the disk.
>+# https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_table_header_(LBA_1)
>+#
>+magic="$(dd if="$dev" bs=1 skip=$sector_size count=8 2>/dev/null)"
> if [ "$magic" = "EFI PART" ]; then
> 	partition_table='gpt'
>+	# Number of partition entries, 4 bytes little-endian.
> 	magic=$(read_gpt 80)
> else
> 	partition_table='msdos'
>@@ -125,16 +142,26 @@ verbose "Partition table: $partition_table"
> 	fatal "invalid partition number: $partition"
> 
> if [ "$partition_table" = "msdos" ]; then
>+	# MBR partition table starts at offset 446.
>+	# Each element of the table occupying 16 bytes.
> 	magic=$((16 * ($partition - 1) + 446))
> 	magic="$(dd if="$dev" bs=1 skip=$magic count=1 2>/dev/null | base64)"
>+	# First byte of the element is 0x80 for the boot partition.
>+	# https://en.wikipedia.org/wiki/Master_boot_record#PTE
> 	[ "$magic" = "gA==" ] ||
> 		fatal "partition not bootable"
> 	mbr_bin='mbr.bin'
> else
>+	# Size of a single partition entry, 4 bytes little-endian.
> 	magic=$(read_gpt 84)
>+	# Attribute flags (8 bytes little-endian) starts at offset 48 of the entry.
>+	# https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_entries_(LBA_2-33)
> 	magic=$(($magic * ($partition - 1) + 48))
>+	# We interested only low byte of the attribute flags and only bit "2" (mask 0x04).
> 	magic=$(read_entry $magic)
> 	magic=$(($magic & 4))
>+	# If the bit "2" of the attribute flags is set,
>+	# partition is marked as bootable in the Legacy BIOS.
> 	[ "$magic" = "4" ] ||
> 		fatal "partition not bootable"
> 	mbr_bin='gptmbr.bin'

Actions: View | Diff

Attachments on bug 34481: 7432 | 7435 | 7446