On 10/07/2013 7:48 AM, Darren Hart wrote:
On Wed, 2013-07-10 at 00:12 +1000, Jonathan Liu wrote:
The root device is currently set as /dev/hda2. However, this is
only correct if it's the first IDE drive. If booting off the first SATA
drive instead, it would be /dev/sda2. It's not the first drive, neither
/dev/hda2 or /dev/sda2 would be correct.
The solution to this has typically been to use the filesystem UUID to
specify the root device but this requires extra support in the initrd.
Linux 3.8 introduces the ability to specify the root device using the
MBR disk signature and the partition number which is much simpler to
use and avoids the extra overhead of an initrd.
This change uses the MBR disk signature to specify the root device when
using Linux 3.8+ and CONFIG_BLOCK (required for root=PARTUUID=)
is enabled in the kernel.
This has been tested with QEMU x86 and Intel Desktop Board D2500HN using
an image recipe inheriting boot-directdisk and core-image.
Signed-off-by: Jonathan Liu <net...@gmail.com>
---
meta/classes/boot-directdisk.bbclass | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/meta/classes/boot-directdisk.bbclass
b/meta/classes/boot-directdisk.bbclass
index efeadab..f97060f 100644
--- a/meta/classes/boot-directdisk.bbclass
+++ b/meta/classes/boot-directdisk.bbclass
@@ -35,7 +35,9 @@ BOOTDD_EXTRA_SPACE ?= "16384"
# Get the build_syslinux_cfg() function from the syslinux class
AUTO_SYSLINUXCFG = "1"
-SYSLINUX_ROOT ?= "root=/dev/sda2"
+SYSLINUX_FIXED_ROOT = "root=/dev/sda2"
+SYSLINUX_UUID_ROOT = "root=PARTUUID=${DISK_SIGNATURE}-02"
Why '=' and not '?=' for the above? Shouldn't the user be able to
override these?
Ok.
+SYSLINUX_ROOT ?= "${@'${SYSLINUX_UUID_ROOT}' if has_kernel_mbr_partuuid_support(d)
else '${SYSLINUX_FIXED_ROOT}'}"
SYSLINUX_TIMEOUT ?= "10"
inherit syslinux
@@ -98,6 +100,10 @@ build_boot_dd() {
parted $IMAGE set 1 boot on
parted $IMAGE print
+ # Disk signature generated by parted isn't really random, so use our own generated signature
+ echo -ne "$(echo ${DISK_SIGNATURE} | fold -w 2 | tac | paste -sd '' | sed
's/\(..\)/\\x&/g')" | \
+ dd of=$IMAGE bs=1 seek=440 conv=notrunc
Oi! So, can "fold -w 2 | tac | paste -sd '' be replaced with "rev" from
the standard util-linux package?
And the sed command... just insert "\x" every two characters? That
doesn't seem to add any more randomness.... maybe I'm missing the point
here?
fold -w 2 | tac | paste -sd '' is to reverse the hex bytes. the sed
command is to convert the hex bytes aabbccdd to \xaa\xbb\xcc\xdd and
pass to echo -ne to convert the hex bytes to binary. I can remove fold
-w 2 | tac | paste -sd '' and add rev after converting to binary.
+
OFFSET=`expr $END2 / 512`
dd if=${STAGING_DATADIR}/syslinux/mbr.bin of=$IMAGE conv=notrunc
dd if=$HDDIMG of=$IMAGE conv=notrunc seek=1 bs=512
@@ -113,4 +119,26 @@ python do_bootdirectdisk() {
bb.build.exec_func('build_boot_dd', d)
}
+def generate_disk_signature():
+ import uuid
+ return str(uuid.uuid4())[:8]
+
+def get_kernel_version(d):
+ import subprocess
+ version_cmd = r"grep '^VERSION\s*=' '%s/Makefile' | grep -o '[0-9]*$'" %
(d.getVar("STAGING_KERNEL_DIR", True))
+ version = int(subprocess.Popen(version_cmd, shell=True,
stdout=subprocess.PIPE).communicate()[0])
+ patchlevel_cmd = r"grep '^PATCHLEVEL\s*=' '%s/Makefile' | grep -o '[0-9]*$'" %
(d.getVar("STAGING_KERNEL_DIR", True))
+ patchlevel = int(subprocess.Popen(patchlevel_cmd, shell=True,
stdout=subprocess.PIPE).communicate()[0])
+ return (version, patchlevel)
+
+def has_kernel_config_option(option, d):
+ import subprocess
+ grep_cmd = r"grep '^CONFIG_%s=y$' '%s/.config'" % (option,
d.getVar("STAGING_KERNEL_DIR", True))
+ return subprocess.call(grep_cmd, shell=True, stdout=subprocess.PIPE) == 0
Is there a specific kernel option to test for the MBR disk signature
support or is that inherent in the block drivers now? It would be nice
if we could skip the kernel version check, that code looks dangerously
fragile (no fault of yours).
The commit which adds the support is
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=d33b98fc82b0908e91fb05ae081acaed7323f9d2.
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/init/do_mounts.c?id=refs/tags/v3.8.13
indicates PARTUUID= support is only enabled with CONFIG_BLOCK.
Alternatively, instead of checking kernel version I could just add an
option to enable the PARTUUID support and add a comment in the class
that you need Linux 3.8+ with CONFIG_BLOCK. It would be disabled by
default in that case and if they are using an older kernel version with
the feature manually backported, they can explicitly enable it.
+
+def has_kernel_mbr_partuuid_support(d):
+ return get_kernel_version(d) >= (3, 8) and
has_kernel_config_option("BLOCK", d)
+
+DISK_SIGNATURE := "${@generate_disk_signature()}"
+
addtask bootdirectdisk before do_build
Regards,
Jonathan
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