On Mon, Oct 14, 2024 at 1:10 PM Leo Sandoval <lsand...@redhat.com> wrote:
>
> From: Michael Chang <mch...@suse.com>
>
> This patch enables the use of a relative path to the btrfs default subvolume
> by
> setting the environment variable btrfs_relative_path=[y1]. In contrast to
> using
> an absolute path from the toplevel root, which always reads files consistently
> from a fixed location, the relative path allows grub to follow changes in the
> default subvolume, which might occur as a consequence of a rollback operation.
>
> The btrfs_relative_path environment variable is available but not enabled by
> default, so the default path remains aligned with the upstream definition. For
> systems that do not require btrfs rollback or booting from snapshots, an
> absolute path is preferred, as it makes path handling consistent with other
> non-btrfs filesystems and allows file access throughout the filesystem
> regardless of subvolumes, etc.
>
> Signed-off-by: Michael Chang <mch...@suse.com>
> Signed-off-by: Robbie Harwood <rharw...@redhat.com>
> ---
> grub-core/fs/btrfs.c | 107 ++++++++++++++++++++++++++++++-------------
> 1 file changed, 76 insertions(+), 31 deletions(-)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index 14e38a4df..d47f9ab03 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -1335,6 +1335,7 @@ grub_btrfs_mount (grub_device_t dev)
> {
> struct grub_btrfs_data *data;
> grub_err_t err;
> + const char *relpath = grub_env_get ("btrfs_relative_path");
>
> if (!dev->disk)
> {
> @@ -1365,11 +1366,14 @@ grub_btrfs_mount (grub_device_t dev)
> data->devices_attached[0].dev = dev;
> data->devices_attached[0].id = data->sblock.this_device.device_id;
>
> - err = btrfs_handle_subvol (data);
> - if (err)
> + if (relpath && (relpath[0] == '1' || relpath[0] == 'y'))
> {
> - grub_free (data);
> - return NULL;
> + err = btrfs_handle_subvol (data);
> + if (err)
> + {
> + grub_free (data);
> + return NULL;
> + }
> }
>
> return data;
> @@ -1966,24 +1970,39 @@ find_path (struct grub_btrfs_data *data,
> grub_size_t allocated = 0;
> struct grub_btrfs_dir_item *direl = NULL;
> struct grub_btrfs_key key_out;
> + int follow_default;
> const char *ctoken;
> grub_size_t ctokenlen;
> char *path_alloc = NULL;
> char *origpath = NULL;
> unsigned symlinks_max = 32;
> + const char *relpath = grub_env_get ("btrfs_relative_path");
>
> + follow_default = 0;
> origpath = grub_strdup (path);
> if (!origpath)
> return grub_errno;
>
> - if (data->fs_tree)
> + if (relpath && (relpath[0] == '1' || relpath[0] == 'y'))
> {
> - *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> - *tree = data->fs_tree;
> - /* This is a tree root, so everything starts at objectid 256 */
> - key->object_id = grub_cpu_to_le64_compile_time
> (GRUB_BTRFS_OBJECT_ID_CHUNK);
> - key->type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> - key->offset = 0;
> + if (data->fs_tree)
> + {
> + *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> + *tree = data->fs_tree;
> + /* This is a tree root, so everything starts at objectid 256 */
> + key->object_id = grub_cpu_to_le64_compile_time
> (GRUB_BTRFS_OBJECT_ID_CHUNK);
> + key->type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> + key->offset = 0;
> + }
> + else
> + {
> + *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> + *tree = data->sblock.root_tree;
> + key->object_id = data->sblock.root_dir_objectid;
> + key->type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> + key->offset = 0;
> + follow_default = 1;
> + }
> }
> else
> {
> @@ -1994,15 +2013,23 @@ find_path (struct grub_btrfs_data *data,
>
> while (1)
> {
> - while (path[0] == '/')
> - path++;
> - if (!path[0])
> - break;
> - slash = grub_strchr (path, '/');
> - if (!slash)
> - slash = path + grub_strlen (path);
> - ctoken = path;
> - ctokenlen = slash - path;
> + if (!follow_default)
> + {
> + while (path[0] == '/')
> + path++;
> + if (!path[0])
> + break;
> + slash = grub_strchr (path, '/');
> + if (!slash)
> + slash = path + grub_strlen (path);
> + ctoken = path;
> + ctokenlen = slash - path;
> + }
> + else
> + {
> + ctoken = "default";
> + ctokenlen = sizeof ("default") - 1;
> + }
>
> if (*type != GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY)
> {
> @@ -2013,7 +2040,9 @@ find_path (struct grub_btrfs_data *data,
>
> if (ctokenlen == 1 && ctoken[0] == '.')
> {
> - path = slash;
> + if (!follow_default)
> + path = slash;
> + follow_default = 0;
> continue;
> }
> if (ctokenlen == 2 && ctoken[0] == '.' && ctoken[1] == '.')
> @@ -2044,8 +2073,9 @@ find_path (struct grub_btrfs_data *data,
> *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> key->object_id = key_out.offset;
>
> - path = slash;
> -
> + if (!follow_default)
> + path = slash;
> + follow_default = 0;
> continue;
> }
>
> @@ -2114,7 +2144,9 @@ find_path (struct grub_btrfs_data *data,
> return err;
> }
>
> - path = slash;
> + if (!follow_default)
> + path = slash;
> + follow_default = 0;
> if (cdirel->type == GRUB_BTRFS_DIR_ITEM_TYPE_SYMLINK)
> {
> struct grub_btrfs_inode inode;
> @@ -2164,14 +2196,26 @@ find_path (struct grub_btrfs_data *data,
> path = path_alloc = tmp;
> if (path[0] == '/')
> {
> - if (data->fs_tree)
> + if (relpath && (relpath[0] == '1' || relpath[0] == 'y'))
> {
> - *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> - *tree = data->fs_tree;
> - /* This is a tree root, so everything starts at objectid
> 256 */
> - key->object_id = grub_cpu_to_le64_compile_time
> (GRUB_BTRFS_OBJECT_ID_CHUNK);
> - key->type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> - key->offset = 0;
> + if (data->fs_tree)
> + {
> + *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> + *tree = data->fs_tree;
> + /* This is a tree root, so everything starts at
> objectid 256 */
> + key->object_id = grub_cpu_to_le64_compile_time
> (GRUB_BTRFS_OBJECT_ID_CHUNK);
> + key->type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> + key->offset = 0;
> + }
> + else
> + {
> + *type = GRUB_BTRFS_DIR_ITEM_TYPE_DIRECTORY;
> + *tree = data->sblock.root_tree;
> + key->object_id = data->sblock.root_dir_objectid;
> + key->type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> + key->offset = 0;
> + follow_default = 1;
> + }
> }
> else
> {
> @@ -2922,6 +2966,7 @@ GRUB_MOD_INIT (btrfs)
> subvolid_set_env);
> grub_env_export ("btrfs_subvol");
> grub_env_export ("btrfs_subvolid");
> + grub_env_export ("btrfs_relative_path");
> }
>
> GRUB_MOD_FINI (btrfs)
> --
> 2.46.2
>
LGTM. :)
Reviewed-by: Neal Gompa <ngomp...@gmail.com>
--
真実はいつも一つ！/ Always, there's only one truth!
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