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Kernel: Parse cmdline for root filesystem e.g. root=/dev/hda1

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This introduces very basic handling of the kernel command line to choose
the root filesystem at startup. Given that we currently only support a
single IDE hard drive, it's hard-coded to look for `/dev/hda` at the start
of the argument.

If there is nothing following this, or if the parameter is empty,
init_stage2 will try to load the ext2 filesystem from the start of the
device. This is intended to be the default behaviour when running
development builds, as it is faster to set up and doesn't require a
working grub installation.

If `/dev/hda` is followed by a number, init_stage2 will try to read an MBR
partition header from the drive, then load the requested partition. It
will reject non-numeric trailing data, and anything outside of partitions
one through four.
This commit is contained in:
Conrad Pankoff 2019-06-04 22:03:35 +10:00 • committed by Andreas Kling
parent d7734bf232
commit 0aa1f1c2d6
2 changed files with 43 additions and 15 deletions
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56
Kernel/init.cpp
View file

@ -69,26 +69,54 @@ VFS* vfs;
auto dev_random = make<RandomDevice>();
auto dev_ptmx = make<PTYMultiplexer>();
// TODO: decide what drive/partition to use based on cmdline from
// bootloader. currently hardcoded to the equivalent of hd0,1.
auto root = KParams::the().get("root");
if (root.is_empty()) {
root = "/dev/hda";
}
if (!root.starts_with("/dev/hda")) {
kprintf("init_stage2: root filesystem must be on the first IDE hard drive (/dev/hda)\n");
hang();
}
auto dev_hd0 = IDEDiskDevice::create();
MBRPartitionTable dev_hd0pt(dev_hd0.copy_ref());
if (!dev_hd0pt.initialize()) {
kprintf("init_stage2: couldn't read MBR from disk");
hang();
Retained<DiskDevice> root_dev = dev_hd0.copy_ref();
root = root.substring(strlen("/dev/hda"), root.length() - strlen("/dev/hda"));
if (root.length()) {
bool ok;
unsigned partition_number = root.to_uint(ok);
if (!ok) {
kprintf("init_stage2: couldn't parse partition number from root kernel parameter\n");
hang();
}
if (partition_number < 1 || partition_number > 4) {
kprintf("init_stage2: invalid partition number %d; expected 1 to 4\n", partition_number);
hang();
}
MBRPartitionTable mbr(root_dev.copy_ref());
if (!mbr.initialize()) {
kprintf("init_stage2: couldn't read MBR from disk\n");
hang();
}
auto partition = mbr.partition(partition_number);
if (!partition) {
kprintf("init_stage2: couldn't get partition %d\n", partition_number);
hang();
}
root_dev = *partition;
}
auto dev_hd0p1 = dev_hd0pt.partition(1);
if (!dev_hd0p1) {
kprintf("init_stage2: couldn't get first partition");
hang();
}
auto e2fs = Ext2FS::create(*dev_hd0p1.copy_ref());
auto e2fs = Ext2FS::create(root_dev.copy_ref());
if (!e2fs->initialize()) {
kprintf("init_stage2: couldn't open root filesystem");
kprintf("init_stage2: couldn't open root filesystem\n");
hang();
}