[PATCH] erofs-utils: fsck: support extracting subtrees

[Gao Xiang]

Hi Inseob,

On 2026/2/26 08:59, Inseob Kim wrote:
> Add --nid and --path options to fsck.erofs to allow users to check
> or extract specific sub-directories or files instead of the entire
> filesystem.
> 
> This is useful for targeted data recovery or verifying specific
> image components without the overhead of a full traversal.

Thanks for the patch!

> 
> Signed-off-by: Inseob Kim <inseob at google.com>
> ---
>   fsck/main.c | 50 ++++++++++++++++++++++++++++++++++++++++----------
>   1 file changed, 40 insertions(+), 10 deletions(-)
> 
> diff --git a/fsck/main.c b/fsck/main.c
> index ab697be..a7d9f46 100644
> --- a/fsck/main.c
> +++ b/fsck/main.c
> @@ -39,6 +39,8 @@ struct erofsfsck_cfg {
>   	bool preserve_owner;
>   	bool preserve_perms;
>   	bool dump_xattrs;
> +	erofs_nid_t nid;
> +	const char *inode_path;
>   	bool nosbcrc;
>   };
>   static struct erofsfsck_cfg fsckcfg;
> @@ -59,6 +61,8 @@ static struct option long_options[] = {
>   	{"offset", required_argument, 0, 12},
>   	{"xattrs", no_argument, 0, 13},
>   	{"no-xattrs", no_argument, 0, 14},
> +	{"nid", required_argument, 0, 15},
> +	{"path", required_argument, 0, 16},
>   	{"no-sbcrc", no_argument, 0, 512},
>   	{0, 0, 0, 0},
>   };
> @@ -110,6 +114,8 @@ static void usage(int argc, char **argv)
>   		" --extract[=X]          check if all files are well encoded, optionally\n"
>   		"                        extract to X\n"
>   		" --offset=#             skip # bytes at the beginning of IMAGE\n"
> +		" --nid=#                check or extract from the target inode of nid #\n"
> +		" --path=X               check or extract from the target inode of path X\n"
>   		" --no-sbcrc             bypass the superblock checksum verification\n"
>   		" --[no-]xattrs          whether to dump extended attributes (default off)\n"
>   		"\n"
> @@ -245,6 +251,12 @@ static int erofsfsck_parse_options_cfg(int argc, char **argv)
>   		case 14:
>   			fsckcfg.dump_xattrs = false;
>   			break;
> +		case 15:
> +			fsckcfg.nid = (erofs_nid_t)atoll(optarg);
> +			break;
> +		case 16:
> +			fsckcfg.inode_path = optarg;
> +			break;
>   		case 512:
>   			fsckcfg.nosbcrc = true;
>   			break;
> @@ -981,7 +993,8 @@ static int erofsfsck_check_inode(erofs_nid_t pnid, erofs_nid_t nid)
>   
>   	if (S_ISDIR(inode.i_mode)) {
>   		struct erofs_dir_context ctx = {
> -			.flags = EROFS_READDIR_VALID_PNID,
> +			.flags = (pnid == nid && nid != g_sbi.root_nid) ?

Does it relax the validatation check?

and does (nid == pnid && nid == fsckcfg.nid) work?

> +				0 : EROFS_READDIR_VALID_PNID,
>   			.pnid = pnid,
>   			.dir = &inode,
>   			.cb = erofsfsck_dirent_iter,
> @@ -1033,6 +1046,8 @@ int main(int argc, char *argv[])
>   	fsckcfg.preserve_owner = fsckcfg.superuser;
>   	fsckcfg.preserve_perms = fsckcfg.superuser;
>   	fsckcfg.dump_xattrs = false;
> +	fsckcfg.nid = 0;
> +	fsckcfg.inode_path = NULL;
>   
>   	err = erofsfsck_parse_options_cfg(argc, argv);
>   	if (err) {
> @@ -1068,22 +1083,37 @@ int main(int argc, char *argv[])
>   	if (fsckcfg.extract_path)
>   		erofsfsck_hardlink_init();
>   
> -	if (erofs_sb_has_fragments(&g_sbi) && g_sbi.packed_nid > 0) {
> -		err = erofs_packedfile_init(&g_sbi, false);
> +	if (fsckcfg.inode_path) {
> +		struct erofs_inode inode = { .sbi = &g_sbi };
> +
> +		err = erofs_ilookup(fsckcfg.inode_path, &inode);
>   		if (err) {
> -			erofs_err("failed to initialize packedfile: %s",
> -				  erofs_strerror(err));
> +			erofs_err("failed to lookup %s", fsckcfg.inode_path);
>   			goto exit_hardlink;
>   		}

It would be better to check if it's a directory.

Thanks,
Gao Xiang

> +		fsckcfg.nid = inode.nid;
> +	} else if (!fsckcfg.nid) {
> +		fsckcfg.nid = g_sbi.root_nid;
> +	}
>   
> -		err = erofsfsck_check_inode(g_sbi.packed_nid, g_sbi.packed_nid);
> -		if (err) {
> -			erofs_err("failed to verify packed file");
> -			goto exit_packedinode;
> +	if (!fsckcfg.inode_path && fsckcfg.nid == g_sbi.root_nid) {
> +		if (erofs_sb_has_fragments(&g_sbi) && g_sbi.packed_nid > 0) {
> +			err = erofs_packedfile_init(&g_sbi, false);
> +			if (err) {
> +				erofs_err("failed to initialize packedfile: %s",
> +					  erofs_strerror(err));
> +				goto exit_hardlink;
> +			}
> +
> +			err = erofsfsck_check_inode(g_sbi.packed_nid, g_sbi.packed_nid);
> +			if (err) {
> +				erofs_err("failed to verify packed file");
> +				goto exit_packedinode;
> +			}
>   		}
>   	}
>   
> -	err = erofsfsck_check_inode(g_sbi.root_nid, g_sbi.root_nid);
> +	err = erofsfsck_check_inode(fsckcfg.nid, fsckcfg.nid);
>   	if (fsckcfg.corrupted) {
>   		if (!fsckcfg.extract_path)
>   			erofs_err("Found some filesystem corruption");