cfs/boot: Handle separate /boot mount by Johan-Liebert1 · Pull Request #2440 · bootc-dev/bootc

Johan-Liebert1 · 2026-09-08T06:54:17Z

If /boot is mounted as XBOOTLDR partition then grub configs are stored there as we were unconditionally searching for grub configs in /sysroot/boot, which would fail every time. Fix this by checking if /boot is a mountpoint and then checking if we have grub configs in there.

This is only an issue with Grub as GrubCC and SystemdBoot both do not store anything inside of /sysroot/boot and will (should) always have the ESP mounted at /boot

Closes: #2399

If /boot is mounted as XBOOTLDR partition then grub configs are stored there as we were unconditionally searching for grub configs in `/sysroot/boot`, which would fail every time. Fix this by checking if `/boot` is a mountpoint and then checking if we have grub configs in there. This is only an issue with Grub as GrubCC and SystemdBoot both do not store anything inside of `/sysroot/boot` and will (should) always have the ESP mounted at /boot Closes: bootc-dev#2399 Signed-off-by: Pragyan Poudyal <pragyanpoudyal41999@gmail.com>

cgwalters · 2026-09-08T12:29:09Z

will (should) always have the ESP mounted at /boot

Actually won't it be at /efi if that dir exists? We need to handle that

Johan-Liebert1 · 2026-09-08T12:54:17Z

Oh, you're right, that's the case with both ESP and XBOOTLDR. So this needs to be updated for the other two bootloaders as well. I'll add that

Johan-Liebert1 · 2026-09-09T03:51:00Z

So this isn't actually an issue for us since we manually search for the ESP and temp mount it to get a handle. Trying the following setup, everything works as intended

[root@fedora boot]# findmnt /boot
TARGET SOURCE    FSTYPE OPTIONS
/boot  systemd-1 autofs rw,relatime,fd=89,pgrp=1,timeout=120,minproto=5,maxproto=5,direct,pipe_ino=9419
/boot  /dev/vda2 ext4   ro,relatime,seclabel

[root@fedora boot]# findmnt /efi
TARGET SOURCE    FSTYPE OPTIONS
/efi   systemd-1 autofs rw,relatime,fd=94,pgrp=1,timeout=120,minproto=5,maxproto=5,direct,pipe_ino=9447
/efi   /dev/vda1 vfat   rw,nosuid,nodev,noexec,relatime,nosymfollow,fmask=0177,dmask=0077,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro

[root@fedora boot]# fdisk -l
Disk /dev/vda: 10 GiB, 10737418240 bytes, 20971520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 78C1B509-AC00-4417-ADB9-8B2C1E481990

Device       Start      End  Sectors Size Type
/dev/vda1     2048  2099199  2097152   1G EFI System
/dev/vda2  2099200  4196351  2097152   1G Linux extended boot
/dev/vda3  4196352 20969471 16773120   8G Linux root (x86-64)

[root@fedora boot]# bootc status
[  240.313722] EXT4-fs (vda3): re-mounted df0fd0e2-f9f1-4e2d-b90f-515d284dde04.
● Booted image: localhost/bootc-bls
        Digest: sha256:026acb94e25c5b9a4c2f45a790377f8699434df90be3d033b6f1652cfaa524e3 (amd64)
        Verity: 641f49373ed6d35f6b274d8e8216ba39e63aa4378d150f404a09ba54f200f46241b1a72639b966513912da3715c3258f9259c345168bfe1909d5ce98f2cbc718
       Version: 44.20260908.0 (2026-09-09T03:29:24Z)

Johan-Liebert1 · 2026-09-09T04:03:14Z

Also, currently, we just put everything in the ESP (for SystemdBoot and GrubCC) so I don't think this would be an issue for us. @cgwalters hope I'm not missing some use case here?

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🟡 Changes recommended

Upgrade paths still target /sysroot/boot, while mutating callers receive a read-only /boot handle.

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Pull request overview

Updates composefs GRUB boot-directory discovery for systems with a separately mounted /boot.

Changes:

Detects whether /boot is mounted.
Selects /boot when it contains GRUB data; otherwise uses /sysroot/boot.
Inspects the mounted filesystem type with findmnt.

File summaries

File	Description
`crates/lib/src/store/mod.rs`	Adds runtime GRUB boot-directory selection.

Review details

Suppressed comments (2)

crates/lib/src/store/mod.rs:470

This selection is not propagated to the paths used to stage an upgrade. setup_composefs_bls_boot() still hard-codes /sysroot for BootSetupType::Upgrade (bootc_composefs/boot.rs:748-750) and writes binaries and BLS configuration below /sysroot/boot (boot.rs:784-785, 892-908); the GRUB UKI path similarly derives root_path.join("boot") at line 1123. Consequently bootc upgrade in the linked separate-boot scenario still updates the stale physical-root directory. Thread the selected boot directory/path through both upgrade setup paths.

                    BootloaderKind::GRUBClassic => get_boot_dir_for_grub(&physical_root)?,

crates/lib/src/store/mod.rs:435

This rejects every mounted /boot filesystem outside this hard-coded list, even when it contains the GRUB layout; --boot-mount-spec imposes no corresponding filesystem restriction (install.rs:479-484, 2666-2673). Filesystem type is also not a reliable discriminator between ESP and XBOOTLDR. Probe for the expected GRUB/BLS directories and fall back to the physical-root boot directory instead of making BootedStorage::new() fail on an otherwise valid mount.

        fstype => {
            anyhow::bail!("Unknown fstype {fstype} for /boot")

Files reviewed: 1/1 changed files
Comments generated: 2
Review effort level: Balanced

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cgwalters · 2026-09-14T19:03:22Z

+            if boot.is_dir("grub2") {
+                return Ok(boot);


Hmm right libostree has some code to handle this I think we do need to handle readonly XBOOTLDR (or classic mount)

 }

+#[context("Finding boot for Grub")]
+fn get_boot_dir_for_grub(physical_root: &Dir) -> Result<Dir> {


cgwalters · 2026-09-14T18:25:31Z

+
+        // XBOOTLDR, so grub configs should hopefully be here
+        // but check just in case
+        "ext4" | "xfs" | "btrfs" => {


I see no reason to hardcode this

cgwalters · 2026-09-14T18:28:02Z

@@ -104,6 +105,7 @@ use cap_std_ext::cap_std::fs::{
 use cap_std_ext::dirext::CapStdExtDirExt;
 use fn_error_context::context;

+use ocidir::cap_std::ambient_authority;
 use ostree_ext::container_utils::ostree_booted;
 use ostree_ext::prelude::FileExt;
 use ostree_ext::sysroot::SysrootLock;
@@ -361,6 +363,80 @@ fn sysroot_is_read_only(d: &Dir) -> Result<bool> {
    Ok(false)
 }

+#[context("Finding boot for Grub")]
+fn get_boot_dir_for_grub(physical_root: &Dir) -> Result<Dir> {
+    // We have this so systemd's boot.automount shouldn't expire until
+    // this function finishes execution as we have a handle to /boot
+    let boot =
+        Dir::open_ambient_dir("/boot", ambient_authority()).context("Failed to open /boot")?;
+
+    let is_boot_mntpnt = boot
+        .is_mountpoint(".")
+        .context("Checking if /boot is a mountpoint")?;
+
+    // /boot is not a mount point for bootloader Grub, so we have to
+    // have stuff in /sysroot/boot
+    if !matches!(is_boot_mntpnt, Some(true)) {
+        return physical_root
+            .open_dir("boot")
+            .context("Opening boot in physical root");
+    }
+
+    // /boot is a mountpoint
+    // Figure out if it's the ESP or XBOOTLDR
+    let mnt_res = run_findmnt(&[], None, Some("/boot")).context("Finding /boot mount info")?;
+
+    let mut boot_fs = None;
+
+    for mount in mnt_res.filesystems {
+        if mount.source.starts_with("systemd") {
+            // systemd automount, useless for getting any info
+            continue;
+        }
+
+        if let Some(already_found) = boot_fs {
+            // Really shouldn't happen, but for sanity
+            anyhow::bail!(
+                "Found multiple mounts on /boot. Found {}, already had {already_found}",
+                mount.fstype
+            );
+        };
+
+        boot_fs = Some(mount.fstype);
+    }
+
+    let boot_fs = boot_fs.ok_or_else(|| anyhow::anyhow!("Failed to get filesystem for /boot"))?;
+
+    // NOTE: It would be ideal here to check for DPS UUID but we can't be sure that the
+    // device that /boot is mounted as will have DPS compatible UUID


But we could check it

Johan-Liebert1 requested review from cgwalters and jeckersb September 8, 2026 06:54

cgwalters mentioned this pull request Sep 14, 2026

auto-updates fail with opendir(boot): Operation not permitted when /boot is a systemd automount that has idled out #2402

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cgwalters requested a balanced review from Copilot September 14, 2026 18:23

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cfs/boot: Handle separate /boot mount - #2440

cfs/boot: Handle separate /boot mount#2440
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Johan-Liebert1:issue-2399

Johan-Liebert1 commented Sep 8, 2026

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