Xiaomi Redmi Note 4 (mido) : mmcblk0p49: don't know how to mount this partition

[lathspell]

Backup fails with "don't know how to mount this partition".

$ tetherback -v
tetherback v0.9.1
Found ADB version 1.0.36
Using default transfer method: adb exec-out pipe (--exec-out)
Device reports kernel 3.18.24-perf-g3e8efb0
Device reports TWRP version 3.2.1-0
Reading partition map for mmcblk0 (49 partitions)...
  partition map: 100%                                                                                                                                                                                                                       
Reading partition map for mmcblk0rpmb (0 partitions)...
  partition map: 100%                                                                                                                                                                                                                       

Partition map:

BLOCK DEVICE    PARTITION NAME      SIZE (KiB)  MOUNT POINT    FSTYPE
--------------  ----------------  ------------  -------------  --------
mmcblk0p1       modem                    86016  /firmware      vfat
mmcblk0p2       fsc                          1
mmcblk0p3       ssd                          8
mmcblk0p4       sbl1                       512
mmcblk0p5       sbl1bak                    512
mmcblk0p6       rpm                        512
mmcblk0p7       rpmbak                     512
mmcblk0p8       tz                        2048
mmcblk0p9       tzbak                     2048
mmcblk0p10      devcfg                     256
mmcblk0p11      devcfgbak                  256
mmcblk0p12      dsp                      16384
mmcblk0p13      modemst1                  1536
mmcblk0p14      modemst2                  1536
mmcblk0p15      ddr                         32
mmcblk0p16      fsg                       1536
mmcblk0p17      sec                         16
mmcblk0p18      splash                   11264
mmcblk0p19      aboot                     1024
mmcblk0p20      abootbak                  1024
mmcblk0p21      boot                     65536
mmcblk0p22      recovery                 65536
mmcblk0p23      devinfo                   1024
mmcblk0p24      system                 3145728  /system        ext4
mmcblk0p25      cache                   262144  /cache         ext4
mmcblk0p26      persist                  32768  /persist       ext4
mmcblk0p27      misc                      1024
mmcblk0p28      keystore                   512
mmcblk0p29      config                      32
mmcblk0p30      oem                     262144
mmcblk0p31      limits                      32
mmcblk0p32      mota                       512
mmcblk0p33      dip                       1024
mmcblk0p34      mdtp                     32768
mmcblk0p35      syscfg                     512
mmcblk0p36      mcfg                      4096
mmcblk0p37      lksecapp                   128
mmcblk0p38      lksecappbak                128
mmcblk0p39      cmnlib                     256
mmcblk0p40      cmnlibbak                  256
mmcblk0p41      cmnlib64                   256
mmcblk0p42      cmnlib64bak                256
mmcblk0p43      keymaster                  256
mmcblk0p44      keymasterbak               256
mmcblk0p45      apdp                       256
mmcblk0p46      msadp                      256
mmcblk0p47      dpo                          8
mmcblk0p48      cust                    851968  /cust          ext4
mmcblk0p49      userdata              25161191
                Total:                30017896

Backup plan:

PARTITION NAME    FILENAME         FORMAT
----------------  ---------------  ------------------------------
boot              boot.emmc.win    gzipped raw image
system            system.ext4.win  tar -cz -p
userdata          data.ext4.win    tar -cz -p --exclude="*-cache"

Saving backup images in ./twrp-backup-2019-03-09--12-57-18/ ...
Saving partition boot (mmcblk0p21), 64 MiB uncompressed...
  boot.emmc.win: 100%   7.0 MiB/s  17.2 MiB                                                                                                                                                                                                 
Saving tarball of mmcblk0p24 (mounted at /system), 3072 MiB uncompressed...
  system.ext4.win: 100%   8.2 MiB/s 605.3 MiB                                                                                                                                                                                               
Traceback (most recent call last):
  File "/usr/local/bin/tetherback", line 11, in <module>
    load_entry_point('tetherback==0.9.1', 'console_scripts', 'tetherback')()
  File "/home/cb/.local/lib/python3.5/site-packages/tetherback/tetherback.py", line 344, in main
    backup_partition(adb, partmap[standard], bp, args.transport, backupdir, args.verify)
  File "/home/cb/.local/lib/python3.5/site-packages/tetherback/tetherback.py", line 230, in backup_partition
    raise RuntimeError("%s: don't know how to mount this partition" % pi.devname)
RuntimeError: mmcblk0p49: don't know how to mount this partition

$ adb shell cat /etc/fstab
/dev/block/mmcblk0p24 /system ext4 rw 0 0
/dev/block/dm-0 /data ext4 rw 0 0
/dev/block/mmcblk0p25 /cache ext4 rw 0 0
/dev/block/mmcblk0p48 /cust ext4 rw 0 0
/dev/block/mmcblk0p1 /firmware vfat rw 0 0
/dev/block/mmcblk0p26 /persist ext4 rw 0 0
 /sdcard1 auto rw 0 0
 /usb-otg auto rw 0 0

[PedroHLC]

mmcblk0p49 is userdata, but encrypted. Seems like dm-0 should be used instead.