nand下可用作ubifs文件系统的最小mtd分区大小

验证结论

对于nand上的mtd分区，如果想要成功挂载为ubifs系统，mtd分区大小至少为5M。考虑到保留2块（256k）作为边界保护。mtd分区至少为 5120K + 256K = 5376K。

验证过程

mtd 分区大小为4M的失败验证

x
mtd10: 00440000 00020000 "0:XINFO"

/dev/mtd10 大小位 0x440000 = 4352k

按如下操作流程

Step1: 生成UBI设备

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mtd erase /dev/mtd10
ubiattach -p /dev/mtd10

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root@AP-:~# ubiattach -p /dev/mtd10
UBI device number 2, total 34 LEBs (4317184 bytes, 4.1 MiB), available 0 LEBs (0 bytes), LEB size 126976 bytes (124.0 KiB)

root@AP-:~# ubinfo /dev/ubi2
ubi2
Volumes count:                           1
Logical eraseblock size:                 126976 bytes, 124.0 KiB
Total amount of logical eraseblocks:     34 (4317184 bytes, 4.1 MiB)
Amount of available logical eraseblocks: 0 (0 bytes)
Maximum count of volumes                 128
Count of bad physical eraseblocks:       0
Count of reserved physical eraseblocks:  20
Current maximum erase counter value:     2
Minimum input/output unit size:          2048 bytes
Character device major/minor:            235:0
Present volumes:                         0

Step2: 创建卷

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ubimkvol /dev/ubi2 -N newx -m

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root@AP-:~# ubinfo /dev/ubi2_0 
Volume ID:   0 (on ubi2)
Type:        dynamic
Alignment:   1
Size:        10 LEBs (1269760 bytes, 1.2 MiB)
State:       OK
Name:        newx
Character device major/minor: 235:1

Step3: 挂载卷

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mkdir /tmp/xxx
mount -t ubifs /dev/ubi2_0 /tmp/xxx/

挂载失败的错误原因分析

root@AP-:~# mount -t ubifs /dev/ubi2_0 /tmp/xxx/
mount: wrong fs type, bad option, bad superblock on /dev/ubi2_0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
root@AP-:~# dmesg | tail -n 3
[ 1821.308864] UBIFS (ubi1:0): background thread "ubifs_bgt1_0" stops
[ 1849.640137] UBIFS error (ubi2:0 pid 26396): init_constants_early: too few LEBs (10), min. is 17
[ 1907.159879] UBIFS error (ubi2:0 pid 27961): init_constants_early: too few LEBs (10), min. is 17

=> 即至少需要 17 个LEB 才能挂载。

mtd 分区大小为5M的成功验证

分区大小

x
mtd10: 00540000 00020000 "0:XINFO"

/dev/mtd10 大小位 0x540000 = 5376k

Step1: 生成UBI设备

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mtd erase /dev/mtd10
ubiattach -p /dev/mtd10

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root@AP-:~# ubiattach -p /dev/mtd10
UBI device number 2, total 42 LEBs (5332992 bytes, 5.1 MiB), available 18 LEBs (2285568 bytes, 2.2 MiB), LEB size 126976 bytes (124.0 KiB)

Step2: 创建卷

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ubimkvol /dev/ubi2 -N newx -m

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root@AP-:~# ubimkvol /dev/ubi2 -N newx -m
Set volume size to 2285568
Volume ID 0, size 18 LEBs (2285568 bytes, 2.2 MiB), LEB size 126976 bytes (124.0 KiB), dynamic, name "newx", alignment 1
root@AP-:~# ubinfo /dev/ubi2_0 
Volume ID:   0 (on ubi2)
Type:        dynamic
Alignment:   1
Size:        18 LEBs (2285568 bytes, 2.2 MiB)
State:       OK
Name:        newx
Character device major/minor: 235:1

Step3: 挂载卷

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mkdir /tmp/xxx
mount -t ubifs /dev/ubi2_0 /tmp/xxx/

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root@AP-:/tmp/xxx# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/ubi2_0             456.0K     20.0K    376.0K   5% /tmp/xxx

root@AP-:~# mount
/dev/ubi2_0 on /tmp/xxx type ubifs (rw,relatime)