From 45748ff060e6935031cf1b34aae6025adcc7eedd Mon Sep 17 00:00:00 2001
From: Silke Hofstra <silke@slxh.eu>
Date: Sat, 4 Jul 2020 15:15:52 +0200
Subject: [PATCH] Add support for Btrfs subvolumes

---
 meson.build                       |  6 ++++++
 src/bootloaders/grub2.c           |  5 +++++
 src/bootloaders/syslinux-common.c |  4 ++++
 src/bootloaders/systemd-class.c   |  4 ++++
 src/lib/probe.c                   | 11 +++++++++++
 src/lib/probe.h                   |  1 +
 src/meson.build                   |  1 +
 7 files changed, 32 insertions(+)

diff --git a/meson.build b/meson.build
index 7c43d5a4..5117f3ed 100644
--- a/meson.build
+++ b/meson.build
@@ -44,6 +44,12 @@ ccompiler = meson.get_compiler('c')
 dep_blkid = dependency('blkid')
 dep_check = dependency('check', version: '>= 0.9')
 
+# other deps
+dep_btrfs = ccompiler.find_library('btrfsutil')
+if not ccompiler.has_header('btrfsutil.h')
+    error('Cannot find btrfsutil.h. Is btrfs-progs-dev(el) installed?')
+endif
+
 # Grab necessary paths
 path_prefix = get_option('prefix')
 path_bindir = join_paths(path_prefix, get_option('bindir'))
diff --git a/src/bootloaders/grub2.c b/src/bootloaders/grub2.c
index 9e2d1da9..b2697c17 100644
--- a/src/bootloaders/grub2.c
+++ b/src/bootloaders/grub2.c
@@ -240,6 +240,11 @@ bool grub2_write_kernel(const Grub2Config *config, const Kernel *kernel)
                                          "rd.luks.uuid=%s ",
                                          config->root_dev->luks_uuid);
         }
+        if (config->root_dev->btrfs_sub) {
+                cbm_writer_append_printf(config->writer,
+                                         "rootflags=subvol=%s ",
+                                         config->root_dev->btrfs_sub);
+        }
 
         /* Finish it off with the command line options */
         cbm_writer_append_printf(config->writer, "%s\"\n", kernel->meta.cmdline);
diff --git a/src/bootloaders/syslinux-common.c b/src/bootloaders/syslinux-common.c
index 8ab3b06c..e3ead038 100644
--- a/src/bootloaders/syslinux-common.c
+++ b/src/bootloaders/syslinux-common.c
@@ -175,6 +175,10 @@ bool syslinux_common_set_default_kernel(const BootManager *manager, const Kernel
                 if (root_dev->luks_uuid) {
                         cbm_writer_append_printf(writer, "rd.luks.uuid=%s ", root_dev->luks_uuid);
                 }
+                /* Add Btrfs information if relevant */
+                if (root_dev->btrfs_sub) {
+                        cbm_writer_append_printf(writer, "rootflags=subvol=%s ", root_dev->btrfs_sub);
+                }
 
                 /* Write out the cmdline */
                 cbm_writer_append_printf(writer, "%s\n", k->meta.cmdline);
diff --git a/src/bootloaders/systemd-class.c b/src/bootloaders/systemd-class.c
index d669b6a8..2ea293ee 100644
--- a/src/bootloaders/systemd-class.c
+++ b/src/bootloaders/systemd-class.c
@@ -269,6 +269,10 @@ bool sd_class_install_kernel(const BootManager *manager, const Kernel *kernel)
         if (root_dev->luks_uuid) {
                 cbm_writer_append_printf(writer, "rd.luks.uuid=%s ", root_dev->luks_uuid);
         }
+        /* Add Btrfs information if relevant */
+        if (root_dev->btrfs_sub) {
+                cbm_writer_append_printf(writer, "rootflags=subvol=%s ", root_dev->btrfs_sub);
+        }
 
         /* Finish it off with the command line options */
         cbm_writer_append_printf(writer, "%s\n", kernel->meta.cmdline);
diff --git a/src/lib/probe.c b/src/lib/probe.c
index 60b7b223..9a81baeb 100644
--- a/src/lib/probe.c
+++ b/src/lib/probe.c
@@ -21,6 +21,7 @@
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
 #include <unistd.h>
+#include <btrfsutil.h>
 
 #include "blkid_stub.h"
 #include "files.h"
@@ -255,6 +256,16 @@ CbmDeviceProbe *cbm_probe_path(const char *path)
                 LOG_ERROR("Unable to find UUID for %s: %s", devnode, strerror(errno));
         }
 
+        /* Check if its a Btrfs device */
+        if (btrfs_util_is_subvolume(path) == BTRFS_UTIL_OK) {
+                LOG_DEBUG("Root device is a Btrfs subvolume");
+                enum btrfs_util_error err = btrfs_util_subvolume_path(path, 0, &probe.btrfs_sub);
+                if (err != BTRFS_UTIL_OK) {
+                        LOG_ERROR("Failed to get subvolume of Btrfs filesystem %s: %s",
+                                  path, btrfs_util_strerror(err));
+                }
+        }
+
         /* Check if its a software raid device */
         basenom = basename(devnode);
         if (strncmp(basenom, "md", 2) == 0) {
diff --git a/src/lib/probe.h b/src/lib/probe.h
index 4fc7b4fa..575997b4 100644
--- a/src/lib/probe.h
+++ b/src/lib/probe.h
@@ -26,6 +26,7 @@ typedef struct CbmDeviceProbe {
         char *uuid;      /**< UUID for all partition types */
         char *part_uuid; /**< PartUUID for GPT partitions */
         char *luks_uuid; /**< Parent LUKS UUID for the partition */
+        char *btrfs_sub; /**< Btrfs subvolume of the rootfs */
         bool gpt;        /**<Whether this device belongs to a GPT disk */
 } CbmDeviceProbe;
 
diff --git a/src/meson.build b/src/meson.build
index 5bba913b..d175dc1e 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -68,6 +68,7 @@ libcbm_includes = [
 libcbm_dependencies = [
     link_libnica,
     dep_blkid,
+    dep_btrfs,
 ]
 
 # Special constraints for efi functionality