Add support for Btrfs subvolumes

Author: silkeh

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'))

src/bootloaders/grub2.c

@@ -241,6 +241,11 @@ 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);

src/bootloaders/syslinux-common.c

@@ -189,6 +189,10 @@ 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);

src/bootloaders/systemd-class.c

@@ -284,6 +284,10 @@ 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);

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"
@@ -263,6 +264,16 @@ 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) {

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 */
         dev_t dev;       /**< The device itself */
         bool gpt;        /**<Whether this device belongs to a GPT disk */
 } CbmDeviceProbe;

src/meson.build

@@ -68,6 +68,7 @@ libcbm_includes = [
 libcbm_dependencies = [
     link_libnica,
     dep_blkid,
+    dep_btrfs,
 ]
 
 # Special constraints for efi functionality