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

[Gao Xiang]

On 2025/12/23 09:33, zhaoyifan (H) wrote:
> 
> 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?

It won't handle unmount, just forcibly send
the disconnect command.  It's up to users
to run umount instead.

Thanks,
Gao Xiang

> 
> 
> 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);