On Mon, Oct 14, 2024 at 1:10 PM Leo Sandoval <lsand...@redhat.com> wrote:
>
> From: Michael Chang <mch...@suse.com>
>
> Introduce the "btrfs-get-default-subvol" command to output the default
> subvolume's name or id to the console, or to a variable specified via "-o".
>
> Some example usage:
>
> 1. Output the default subvolume's name or path:
> btrfs-get-default-subvol -p ($root)
> 2. Output the default subvolume's ID or number:
> btrfs-get-default-subvol -n ($root)
> 3. Output the default subvolume's path to a variable "btrfs_prefix":
> btrfs-get-default-subvol -p -o btrfs_prefix ($root)
>
> This is useful in a prebuilt image like `grub.xen`, which is built at a time
> when the guest configuration cannot be determined. In such a setup, trying to
> enable "btrfs_relative_path" in the load configuration may lead to problems if
> the guest image did not enable btrfs snapshots in its configuration.
>
> As a result, when attempting to locate grub.cfg in a guest, it may be
> necessary
> to specify the default subvolume in advance where the grub.cfg resides. The
> script would look like this:
>
> btrfs-get-default-subvol -p -o btrfs_prefix ($root)
> if [ -n "${btrfs_prefix}" ]; then
> configfile "${btrfs_prefix}/boot/grub/grub.cfg"
> else
> configfile "/boot/grub/grub.cfg"
> fi
>
> Signed-off-by: Michael Chang <mch...@suse.com>
> Signed-off-by: Robbie Harwood <rharw...@redhat.com>
> ---
> grub-core/fs/btrfs.c | 238 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 238 insertions(+)
>
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index d47f9ab03..d93e9615a 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -2876,6 +2876,238 @@ out:
> return 0;
> }
>
> +static grub_err_t
> +grub_btrfs_get_parent_subvol_path (struct grub_btrfs_data *data,
> + grub_uint64_t child_id,
> + const char *child_path,
> + grub_uint64_t *parent_id,
> + char **path_out)
> +{
> + grub_uint64_t fs_root = 0;
> + struct grub_btrfs_key key_in = {
> + .object_id = child_id,
> + .type = GRUB_BTRFS_ITEM_TYPE_ROOT_BACKREF,
> + .offset = 0,
> + }, key_out;
> + struct grub_btrfs_root_ref *ref;
> + char *buf;
> + struct grub_btrfs_leaf_descriptor desc;
> + grub_size_t elemsize;
> + grub_disk_addr_t elemaddr;
> + grub_err_t err;
> + char *parent_path;
> +
> + *parent_id = 0;
> + *path_out = 0;
> +
> + err = lower_bound(data, &key_in, &key_out, data->sblock.root_tree,
> + &elemaddr, &elemsize, &desc, 0);
> + if (err)
> + return err;
> +
> + if (key_out.type != GRUB_BTRFS_ITEM_TYPE_ROOT_BACKREF || elemaddr == 0)
> + next(data, &desc, &elemaddr, &elemsize, &key_out);
> +
> + if (key_out.type != GRUB_BTRFS_ITEM_TYPE_ROOT_BACKREF)
> + {
> + free_iterator(&desc);
> + return grub_error(GRUB_ERR_FILE_NOT_FOUND, N_("can't find root
> backrefs"));
> + }
> +
> + buf = grub_malloc(elemsize + 1);
> + if (!buf)
> + {
> + free_iterator(&desc);
> + return grub_errno;
> + }
> +
> + err = grub_btrfs_read_logical(data, elemaddr, buf, elemsize, 0);
> + if (err)
> + {
> + grub_free(buf);
> + free_iterator(&desc);
> + return err;
> + }
> +
> + buf[elemsize] = 0;
> + ref = (struct grub_btrfs_root_ref *)buf;
> +
> + err = get_fs_root(data, data->sblock.root_tree, grub_le_to_cpu64
> (key_out.offset),
> + 0, &fs_root);
> + if (err)
> + {
> + grub_free(buf);
> + free_iterator(&desc);
> + return err;
> + }
> +
> + find_pathname(data, grub_le_to_cpu64 (ref->dirid), fs_root, ref->name,
> &parent_path);
> +
> + if (child_path)
> + {
> + *path_out = grub_xasprintf ("%s/%s", parent_path, child_path);
> + grub_free (parent_path);
> + }
> + else
> + *path_out = parent_path;
> +
> + *parent_id = grub_le_to_cpu64 (key_out.offset);
> +
> + grub_free(buf);
> + free_iterator(&desc);
> + return GRUB_ERR_NONE;
> +}
> +
> +static grub_err_t
> +grub_btrfs_get_default_subvolume_id (struct grub_btrfs_data *data,
> grub_uint64_t *id)
> +{
> + grub_err_t err;
> + grub_disk_addr_t elemaddr;
> + grub_size_t elemsize;
> + struct grub_btrfs_key key, key_out;
> + struct grub_btrfs_dir_item *direl = NULL;
> + const char *ctoken = "default";
> + grub_size_t ctokenlen = sizeof ("default") - 1;
> +
> + *id = 0;
> + key.object_id = data->sblock.root_dir_objectid;
> + key.type = GRUB_BTRFS_ITEM_TYPE_DIR_ITEM;
> + key.offset = grub_cpu_to_le64 (~grub_getcrc32c (1, ctoken, ctokenlen));
> + err = lower_bound (data, &key, &key_out, data->sblock.root_tree,
> &elemaddr, &elemsize,
> + NULL, 0);
> + if (err)
> + return err;
> +
> + if (key_cmp (&key, &key_out) != 0)
> + return grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("file not found"));
> +
> + struct grub_btrfs_dir_item *cdirel;
> + direl = grub_malloc (elemsize + 1);
> + err = grub_btrfs_read_logical (data, elemaddr, direl, elemsize, 0);
> + if (err)
> + {
> + grub_free (direl);
> + return err;
> + }
> + for (cdirel = direl;
> + (grub_uint8_t *) cdirel - (grub_uint8_t *) direl
> + < (grub_ssize_t) elemsize;
> + cdirel = (void *) ((grub_uint8_t *) (direl + 1)
> + + grub_le_to_cpu16 (cdirel->n)
> + + grub_le_to_cpu16 (cdirel->m)))
> + {
> + if (ctokenlen == grub_le_to_cpu16 (cdirel->n)
> + && grub_memcmp (cdirel->name, ctoken, ctokenlen) == 0)
> + break;
> + }
> + if ((grub_uint8_t *) cdirel - (grub_uint8_t *) direl
> + >= (grub_ssize_t) elemsize)
> + {
> + grub_free (direl);
> + err = grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("file not found"));
> + return err;
> + }
> +
> + if (cdirel->key.type != GRUB_BTRFS_ITEM_TYPE_ROOT_ITEM)
> + {
> + grub_free (direl);
> + err = grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("file not found"));
> + return err;
> + }
> +
> + *id = grub_le_to_cpu64 (cdirel->key.object_id);
> + return GRUB_ERR_NONE;
> +}
> +
> +static grub_err_t
> +grub_cmd_btrfs_get_default_subvol (struct grub_extcmd_context *ctxt,
> + int argc, char **argv)
> +{
> + char *devname;
> + grub_device_t dev;
> + struct grub_btrfs_data *data;
> + grub_err_t err;
> + grub_uint64_t id;
> + char *subvol = NULL;
> + grub_uint64_t subvolid = 0;
> + char *varname = NULL;
> + char *output = NULL;
> + int path_only = ctxt->state[1].set;
> + int num_only = ctxt->state[2].set;
> +
> + if (ctxt->state[0].set)
> + varname = ctxt->state[0].arg;
> +
> + if (argc < 1)
> + return grub_error (GRUB_ERR_BAD_ARGUMENT, "device name required");
> +
> + devname = grub_file_get_device_name(argv[0]);
> + if (!devname)
> + return grub_errno;
> +
> + dev = grub_device_open (devname);
> + grub_free (devname);
> + if (!dev)
> + return grub_errno;
> +
> + data = grub_btrfs_mount(dev);
> + if (!data)
> + {
> + grub_device_close (dev);
> + grub_dprintf ("btrfs", "failed to open fs\n");
> + grub_errno = GRUB_ERR_NONE;
> + return 0;
> + }
> +
> + err = grub_btrfs_get_default_subvolume_id (data, &subvolid);
> + if (err)
> + {
> + grub_btrfs_unmount (data);
> + grub_device_close (dev);
> + return err;
> + }
> +
> + id = subvolid;
> + while (id != GRUB_BTRFS_ROOT_VOL_OBJECTID)
> + {
> + grub_uint64_t parent_id;
> + char *path_out;
> +
> + err = grub_btrfs_get_parent_subvol_path (data, grub_cpu_to_le64 (id),
> subvol, &parent_id, &path_out);
> + if (err)
> + {
> + grub_btrfs_unmount (data);
> + grub_device_close (dev);
> + return err;
> + }
> +
> + if (subvol)
> + grub_free (subvol);
> + subvol = path_out;
> + id = parent_id;
> + }
> +
> + if (num_only && path_only)
> + output = grub_xasprintf ("%"PRIuGRUB_UINT64_T" /%s", subvolid, subvol);
> + else if (num_only)
> + output = grub_xasprintf ("%"PRIuGRUB_UINT64_T, subvolid);
> + else
> + output = grub_xasprintf ("/%s", subvol);
> +
> + if (varname)
> + grub_env_set(varname, output);
> + else
> + grub_printf ("%s\n", output);
> +
> + grub_free (output);
> + grub_free (subvol);
> +
> + grub_btrfs_unmount (data);
> + grub_device_close (dev);
> +
> + return GRUB_ERR_NONE;
> +}
> +
> static struct grub_fs grub_btrfs_fs = {
> .name = "btrfs",
> .fs_dir = grub_btrfs_dir,
> @@ -2893,6 +3125,7 @@ static struct grub_fs grub_btrfs_fs = {
>
> static grub_command_t cmd_info;
> static grub_extcmd_t cmd_list_subvols;
> +static grub_extcmd_t cmd_get_default_subvol;
>
> static char *
> subvolid_set_env (struct grub_env_var *var __attribute__ ((unused)),
> @@ -2960,6 +3193,11 @@ GRUB_MOD_INIT (btrfs)
> "[-p|-n] [-o var] DEVICE",
> "Print list of BtrFS subvolumes on "
> "DEVICE.", options);
> + cmd_get_default_subvol = grub_register_extcmd("btrfs-get-default-subvol",
> + grub_cmd_btrfs_get_default_subvol, 0,
> + "[-p|-n] [-o var] DEVICE",
> + "Print default BtrFS subvolume on "
> + "DEVICE.", options);
> grub_register_variable_hook ("btrfs_subvol", subvol_get_env,
> subvol_set_env);
> grub_register_variable_hook ("btrfs_subvolid", subvolid_get_env,
> --
> 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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