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blockdev.rs: add support for saving mbr partitions
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Fixes coreos#957. If a MBR partition is marked to be saved, it will be translated
using best effort to GPT. To elaberate on "best effort"; there is metadata
which is present in GPT but not MBR, so it might not translate 1:1.
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@prestist
prestist committed Nov 16, 2022
1 parent 4cba801 commit 5a62eb8
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Showing 2 changed files with 118 additions and 30 deletions.
2 changes: 1 addition & 1 deletion Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,7 @@ flate2 = "^1.0"
glob = "^0.3"
# disable default-enabled cli in gptman 0.x
gptman = { version = ">= 0.7, < 2", default-features = false }
mbrman = ">= 0.5, < 0.6"
hex = "^0.4"
ignition-config = "0.2"
lazy_static = "^1.4"
Expand All @@ -86,7 +87,6 @@ xz2 = "^0.1"
zstd = { version = ">= 0.10.0, < 0.12.0", features = ["pkg-config"] }

[target.'cfg(target_arch = "s390x")'.dependencies]
mbrman = ">= 0.5, < 0.6"
rand = ">= 0.7, < 0.9"

[dev-dependencies]
Expand Down
146 changes: 117 additions & 29 deletions src/blockdev.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ use anyhow::{anyhow, bail, Context, Result};
use gptman::{GPTPartitionEntry, GPT};
use nix::sys::stat::{major, minor};
use nix::{errno::Errno, mount, sched};
use mbrman::{MBRPartitionEntry, MBR};
use regex::Regex;
use std::collections::{HashMap, HashSet};
use std::fs::{
Expand All @@ -32,7 +33,7 @@ use std::path::{Path, PathBuf};
use std::process::Command;
use std::thread::sleep;
use std::time::Duration;
use uuid::Uuid;
use uuid::{uuid, Uuid};

use crate::cmdline::PartitionFilter;
use crate::util::*;
Expand Down Expand Up @@ -519,6 +520,33 @@ pub struct SavedPartitions {
partitions: Vec<(u32, GPTPartitionEntry)>,
}

fn translate_mbr_types_to_gpt( sys: u8) -> Uuid {
// non inclusive best effort mapping of MBR types to GPT types
match sys {
// Linux filesystem
0x01 => uuid!("0FC63DAF-8483-4772-8E79-3D69D8477DE4"),
// Linux Filesystem Data
0x83 => uuid!("0FC63DAF-8483-4772-8E79-3D69D8477DE4"),
// Linux LVM
0x8e => uuid!("E6D6D379-F507-44C2-A23C-238F2A3DF928"),
// Linux Swap
0x82 => uuid!("0657FD6D-A4AB-43C4-84E5-0933C84B4F4F"),
_ => uuid!("00000000-0000-0000-0000-ffff00000000"),
}
}

fn translate_mbr_to_gpt( mbr_partition: &MBRPartitionEntry) -> GPTPartitionEntry {
let mut gpt_partition = GPTPartitionEntry::empty();

gpt_partition.partition_type_guid = *translate_mbr_types_to_gpt(mbr_partition.sys).as_bytes();
gpt_partition.unique_partition_guid = *Uuid::new_v4().as_bytes();
gpt_partition.starting_lba = u64::from(mbr_partition.starting_lba);
// -1 because the end is inclusive
gpt_partition.ending_lba = u64::from(mbr_partition.starting_lba + mbr_partition.sectors) - 1;
gpt_partition
}


impl SavedPartitions {
/// Create a SavedPartitions for a block device with a sector size.
pub fn new_from_disk(disk: &mut File, filters: &[PartitionFilter]) -> Result<Self> {
Expand Down Expand Up @@ -556,6 +584,7 @@ impl SavedPartitions {
Self::new(disk, sector_size, filters)
}


fn new(disk: &mut File, sector_size: u64, filters: &[PartitionFilter]) -> Result<Self> {
// if there are no filters, ignore existing GPT, since we're going to
// overwrite it
Expand All @@ -565,40 +594,57 @@ impl SavedPartitions {
partitions: Vec::new(),
});
}

// Create a vector of the partitions
let mut partitions = Vec::new();

// read GPT
let gpt = match GPT::find_from(disk) {
Ok(gpt) => gpt,
match GPT::find_from(disk) {
Ok(gpt) => {
// cross-check GPT sector size
Self::verify_gpt_sector_size(&gpt, sector_size)?;

// save partitions accepted by filters
for (i, p) in gpt.iter() {
if Self::matches_filters(i, p, filters) {
partitions.push((i, p.clone()));
}
}
},
Err(gptman::Error::InvalidSignature) => {
// ensure no indexes are listed to be saved from a MBR disk
// we don't need to check for labels since MBR does not support them
// no GPT, check for MBR
if filters
.iter()
.any(|f| matches!(f, PartitionFilter::Index(_, _)))
&& disk_has_mbr(disk).context("checking if disk has an MBR")?
{
bail!("saving partitions from an MBR disk is not yet supported");
}
{
let mbr = MBR::read_from(disk, u32::try_from(sector_size)?).context("reading disk as MBR")?;

// cross-check MBR sector size
Self::verify_mbr_sector_size(&mbr, sector_size)?;

for (i, p) in mbr.iter() {
if Self::matches_filters_mbr(i.try_into().unwrap(), p, filters) {
// if the partition is using any of the last 33 sectors, we need to bail.
if p.starting_lba + p.sectors < mbr.disk_size - 33 {
partitions.push((i.try_into().context("convert usize into u32")?, translate_mbr_to_gpt(p)));
} else {
bail!("MBR partition {} is using the last 33 sectors of the disk, which is not supported by GPT", i);
}
}
}

}
// no GPT on this disk, so no partitions to save
return Ok(Self {
sector_size,
partitions: Vec::new(),
partitions: partitions,
});
}
Err(e) => return Err(e).context("reading partition table"),
};

// cross-check GPT sector size
Self::verify_gpt_sector_size(&gpt, sector_size)?;

// save partitions accepted by filters
let mut partitions = Vec::new();
for (i, p) in gpt.iter() {
if Self::matches_filters(i, p, filters) {
partitions.push((i, p.clone()));
}
}
let result = Self {
sector_size,
partitions,
Expand Down Expand Up @@ -653,6 +699,17 @@ impl SavedPartitions {
}
Ok(())
}

fn verify_mbr_sector_size(mbr: &MBR, sector_size: u64) -> Result<()> {
if u64::from(mbr.sector_size) != sector_size {
bail!(
"MBR sector size {} doesn't match expected {}",
mbr.sector_size,
sector_size
);
}
Ok(())
}

fn matches_filters(i: u32, p: &GPTPartitionEntry, filters: &[PartitionFilter]) -> bool {
use PartitionFilter::*;
Expand All @@ -668,6 +725,19 @@ impl SavedPartitions {
})
}

fn matches_filters_mbr(i: u32, p: &MBRPartitionEntry, filters: &[PartitionFilter]) -> bool {
use PartitionFilter::*;
if !p.is_used() {
return false;
}
filters.iter().any(|f| match f {
Index(Some(first), _) if first.get() > i => false,
Index(_, Some(last)) if last.get() < i => false,
Index(_, _) => true,
_ => false,
})
}

/// Unconditionally write the saved partitions, and only the saved
/// partitions, to the disk. Write a protective MBR and overwrite any
/// MBR boot code. Updating the kernel partition table is the caller's
Expand Down Expand Up @@ -1569,17 +1639,35 @@ mod tests {

// test trying to save partitions from a MBR disk
let mut disk = make_unformatted_disk();
gptman::GPT::write_protective_mbr_into(&mut disk, 512).unwrap();
// label only
SavedPartitions::new(&mut disk, 512, &vec![label("*i*")]).unwrap();
let mut mbr = mbrman::MBR::new_from(&mut disk, 512 as u32, [0xff; 4])
.expect("could not create partition table");

// create a mbr partition to copy over to gpt
mbr[1] = mbrman::MBRPartitionEntry {
boot: mbrman::BOOT_INACTIVE,
first_chs: mbrman::CHS::empty(),
sys: 0x0f,
last_chs: mbrman::CHS::empty(),
starting_lba: 1,
sectors: mbr.disk_size - 5000,
};

mbr.write_into(&mut disk).unwrap();
// index only
assert_eq!(
SavedPartitions::new(&mut disk, 512, &vec![Index(index(1), index(1))])
.unwrap_err()
.to_string(),
"saving partitions from an MBR disk is not yet supported"
);
// label and index
let saved = SavedPartitions::new(&mut disk, 512, &vec![Index(index(1), index(1))]).unwrap();
assert!(saved.is_saved());

// create a mbr partition that uses some of the last 33 sectors of the disk
mbr[1] = mbrman::MBRPartitionEntry {
boot: mbrman::BOOT_INACTIVE,
first_chs: mbrman::CHS::empty(),
sys: 0x0f,
last_chs: mbrman::CHS::empty(),
starting_lba: 1,
sectors: mbr.disk_size - 22,
};
mbr.write_into(&mut disk).unwrap();

assert_eq!(
SavedPartitions::new(
&mut disk,
Expand All @@ -1588,7 +1676,7 @@ mod tests {
)
.unwrap_err()
.to_string(),
"saving partitions from an MBR disk is not yet supported"
"MBR partition 1 is using the last 33 sectors of the disk, which is not supported by GPT"
);

// test sector size mismatch
Expand Down

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