JFFS2

• Overview
• Important Notes
• Development Guidelines

Overview

JFFS2 is a journal-type file system implemented on MTDs. JFFS2 is mainly used in NOR flash memory. It is readable and writable, supports data compression and write leveling, and provides crash/power failure protection.

There are many differences between flash memory and disk media. Therefore, running a disk file system directly on flash memory causes poor performance and security. JFFS2 is introduced as a file system specially designed for flash memory.

JFFS2 in the OpenHarmony kernel is mainly used to manage files of the NOR flash memory and supports multiple partitions.

Important Notes

• The JFFS2 file system is used for NOR flash memory, and NOR flash driver APIs are called. Therefore, before using the JFFS2 file system, ensure that the NOR flash memory is available on the hardware and the driver is initialized (the return value of spinor_init() is 0).

• The system automatically aligns the start address and partition size based on the block size. The valid partition number ranges from 0 to 19.

• mkfs.jffs2 is supported. You can change parameter values based on service requirements.

• When you use open with the parameter O_TRUNC to open a file, the file content will be cleared.

• You can perform the following operation on JFFS2 files: open, close, read, write, seek, opendir, closedir, readdir, readdir_r, rewinddir, statfs, sync, remove, unlink, mkdir, rmdir, rename, stat, stat64, seek64, mmap, mount, umount, chmod, and chown.

• JFFS2 files can be mounted in the read-only attribute. When MS_RDONLY is carried in the mount function, the read-only attribute is enabled. All APIs with the write attribute, such as write, mkdir, and unlink, and files that are opened not by using O_RDONLY, are rejected and the error code EACCESS is returned.

Development Guidelines

Adding a JFFS2 Partition

Call add_mtd_partition to add a JFFS2 partition. This function automatically names the device node in the format of /dev/spinorblk plus the partition number.

The add_mtd_partition function has four parameters. The first parameter indicates the medium, which can be nand or spinor. A JFFS2 partition is used on spinor, whereas nand is provided for a YAFFS2 partition.

The second parameter indicates the start address, and the third parameter indicates the partition size. Both parameters are transferred in hexadecimal format.

The last parameter indicates the partition number, which ranges from 0 to 19.

INT32 uwRet;
if (uwRet = add_mtd_partition("spinor", 0x100000, 0x800000, 0) != 0) {
    dprintf("add jffs2 partition failed, return %d\n", uwRet);
} else {
    dprintf("Mount jffs2 on spinor.\n");
    uwRet = mount("/dev/spinorblk0", "/jffs0", "jffs2", 0, NULL);
    if (uwRet) {
        dprintf("mount jffs2 err %d\n", uwRet);
        dprintf("Mount jffs2 on nor finished.\n");
    }
}

if (uwRet = add_mtd_partition("spinor", 0x900000, 0x200000, 1) != 0) {
    dprintf("add jffs2 partition failed, return %d\n", uwRet);
}

After the partition is added, you can run partition spinor in shell to view the information about the spinor flash partition.

OHOS # partition spinor
spinor partition num:0, dev name:/dev/spinorblk0, mountpt:/jffs0, startaddr:0x0100000,length:0x0800000 
spinor partition num:1, dev name:/dev/spinorblk1, mountpt:(null), startaddr:0x0900000,length:0x0200000

Mounting JFFS2

Call mount() to mount a device node and mount point.

This function has five parameters. The first parameter indicates the device node, which must match the add_mtd_partition() function. The second parameter indicates the mount point. The third parameter indicates the file system type.

The last two parameters indicate the mounting flag and data. The default values are 0 and NULL, respectively. This operation can also be implemented by running the mount command in shell. You do not need to specify the last two parameters.

Mount a JFFS2 file system.

OHOS # mount /dev/spinorblk1 /jffs1 jffs2

If the following information is displayed, the JFFS2 file system is mounted:

OHOS # mount /dev/spinorblk1 /jffs1 jffs2
mount OK

Now, you can read and write the NOR flash memory.

Unmounting JFFS2

Call umount() to unmount the partition. You only need to provide the correct mount point.

Unmount JFFS2.

OHOS # umount /jffs1

If the following information is displayed, the JFFS2 file system is unmounted:

OHOS # umount /jffs1
umount ok

Deleting a JFFS2 Partition

Call delete_mtd_partition to delete an unmounted partition.

This function has two parameters. The first parameter is the partition number, and the second parameter is the medium type. This function corresponds to the add_mtd_partition() function.

INT32 uwRet;
uwRet = delete_mtd_partition(1,"spinor"); 
if(uwRet != 0) {
    printf("delete jffs2 error\n"); 
} else {     
    printf("delete jffs2 ok\n");
}

OHOS # partition spinor 
spinor partition num:0, dev name:/dev/spinorblk0, mountpt:/jffs0, startaddr:0x0100000,length:0x0800000

Creating a JFFS2 File System Image

Use the mkfs.jffs2 tool to create an image. The default page size is 4 KiB, and the default eraseblock size is 64 KiB. The image size adapts to the source directory and is filled with 0xFF, which is an integer multiple of the eraseblock size. The default command is as follows. If the actual parameters are different from the following parameters, use the actual parameters.

./mkfs.jffs2 -d rootfs/ -o rootfs.jffs2

Table 1 Commands