[PATCH 2/2] erofs-utils: mount: add `--disconnect` command

[zhaoyifan (H)]

On 2025/12/22 15:46, Gao Xiang wrote:
> Users can use the new `--disconnect` option to forcibly disconnect or
> abort NBD block devices.
>
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>

Hi Xiang,

It seems

     mount.erofs -u /dev/nbdX

serving the same purpose of --disconnect? Why do we need a separate 
--disconnect subcommand?


Thanks,

Yifan

> ---
>   mount/main.c | 55 +++++++++++++++++++++++++++++++++++++++++++++-------
>   1 file changed, 48 insertions(+), 7 deletions(-)
>
> diff --git a/mount/main.c b/mount/main.c
> index b3b2e0fc33e0..693dba2dc78d 100644
> --- a/mount/main.c
> +++ b/mount/main.c
> @@ -51,6 +51,7 @@ enum erofs_backend_drv {
>   enum erofsmount_mode {
>   	EROFSMOUNT_MODE_MOUNT,
>   	EROFSMOUNT_MODE_UMOUNT,
> +	EROFSMOUNT_MODE_DISCONNECT,
>   	EROFSMOUNT_MODE_REATTACH,
>   };
>   
> @@ -88,13 +89,14 @@ static void usage(int argc, char **argv)
>   		"Manage EROFS filesystem.\n"
>   		"\n"
>   		"General options:\n"
> -		" -V, --version		print the version number of mount.erofs and exit\n"
> -		" -h, --help		display this help and exit\n"
> -		" -o options		comma-separated list of mount options\n"
> -		" -t type[.subtype]	filesystem type (and optional subtype)\n"
> -		" 			subtypes: fuse, local, nbd\n"
> -		" -u 			unmount the filesystem\n"
> -		"    --reattach		reattach to an existing NBD device\n"
> +		" -V, --version         print the version number of mount.erofs and exit\n"
> +		" -h, --help            display this help and exit\n"
> +		" -o options            comma-separated list of mount options\n"
> +		" -t type[.subtype]     filesystem type (and optional subtype)\n"
> +		"                       subtypes: fuse, local, nbd\n"
> +		" -u                    unmount the filesystem\n"
> +		"    --disconnect       abort an existing NBD device forcibly\n"
> +		"    --reattach         reattach to an existing NBD device\n"
>   #ifdef OCIEROFS_ENABLED
>   		"\n"
>   		"OCI-specific options (with -o):\n"
> @@ -271,6 +273,7 @@ static int erofsmount_parse_options(int argc, char **argv)
>   		{"help", no_argument, 0, 'h'},
>   		{"version", no_argument, 0, 'V'},
>   		{"reattach", no_argument, 0, 512},
> +		{"disconnect", no_argument, 0, 513},
>   		{0, 0, 0, 0},
>   	};
>   	char *dot;
> @@ -316,6 +319,9 @@ static int erofsmount_parse_options(int argc, char **argv)
>   		case 512:
>   			mountcfg.mountmode = EROFSMOUNT_MODE_REATTACH;
>   			break;
> +		case 513:
> +			mountcfg.mountmode = EROFSMOUNT_MODE_DISCONNECT;
> +			break;
>   		default:
>   			return -EINVAL;
>   		}
> @@ -1415,6 +1421,33 @@ err_out:
>   	return err < 0 ? err : 0;
>   }
>   
> +static int erofsmount_disconnect(const char *target)
> +{
> +	int nbdnum, err, fd;
> +	struct stat st;
> +
> +	err = lstat(target, &st);
> +	if (err < 0)
> +		return -errno;
> +
> +	if (!S_ISBLK(st.st_mode) || major(st.st_rdev) != EROFS_NBD_MAJOR)
> +		return -ENOTBLK;
> +
> +	nbdnum = erofs_nbd_get_index_from_minor(minor(st.st_rdev));
> +	err = erofs_nbd_nl_disconnect(nbdnum);
> +	if (err == -EOPNOTSUPP) {
> +		fd = open(target, O_RDWR);
> +		if (fd < 0) {
> +			err = -errno;
> +			goto err_out;
> +		}
> +		err = erofs_nbd_disconnect(fd);
> +		close(fd);
> +	}
> +err_out:
> +	return err < 0 ? err : 0;
> +}
> +
>   int main(int argc, char *argv[])
>   {
>   	int err;
> @@ -1443,6 +1476,14 @@ int main(int argc, char *argv[])
>   		return err ? EXIT_FAILURE : EXIT_SUCCESS;
>   	}
>   
> +	if (mountcfg.mountmode == EROFSMOUNT_MODE_DISCONNECT) {
> +		err = erofsmount_disconnect(mountcfg.target);
> +		if (err < 0)
> +			fprintf(stderr, "Failed to disconnect %s: %s\n",
> +				mountcfg.target, erofs_strerror(err));
> +		return err ? EXIT_FAILURE : EXIT_SUCCESS;
> +	}
> +
>   	if (mountcfg.backend == EROFSFUSE) {
>   		err = erofsmount_fuse(mountcfg.device, mountcfg.target,
>   				      mountcfg.fstype, mountcfg.full_options);