mounting ubifs read-only, is it really readonly, not any wirte/erase?

[Caizhiyong]

    I'm using ubifs as root filesystem, and mounted readonly.

    bootargs are:
        console=ttyAMA0,115200 ubi.mtd=3 root=ubi0:ubifs ro rootfstype=ubifsmtdparts=hi_sfc:-(spi);hinand:10M(10M),50M(50M),50M(50M),-(data)
    
    I'm update ubi.img in uboot used command "nand write xxxx", but when kernel (linux 3.4) startup, there are some write/erase operation.

    I'm add prints to the following functions:

        * %-EIO is returned, the physical eraseblock most probably went bad.
        */
        static int do_sync_erase(struct ubi_device *ubi, int pnum)
        {
            int err, retries = 0;
            struct erase_info ei;
            wait_queue_head_t wq;

            dump_stack();
            printk("\n\n\n");
            return 0;

    The stack dump prints as follow:

        [<c0014c64>] (unwind_backtrace+0x0/0xfc) from [<c02a2a2c>] (do_sync_erase+0x8/0x1c)
        [<c02a2a2c>] (do_sync_erase+0x8/0x1c) from [<c02a3818>] (ubi_io_sync_erase+0x304/0x424)
        [<c02a3818>] (ubi_io_sync_erase+0x304/0x424) from [<c02a41e8>] (erase_worker+0x50/0x510)
        [<c02a41e8>] (erase_worker+0x50/0x510) from [<c02a4f80>] (do_work+0x84/0xd4)
        [<c02a4f80>] (do_work+0x84/0xd4) from [<c02a50ac>] (ubi_thread+0xdc/0x188)
        [<c02a50ac>] (ubi_thread+0xdc/0x188) from [<c0039468>] (kthread+0x94/0x98)
        [<c0039468>] (kthread+0x94/0x98) from [<c000f92c>] (kernel_thread_exit+0x0/0x8)

    mtdinfo -a

        mtd2
        Name:                           50M
        Type:                           nand
        Eraseblock size:                131072 bytes, 128.0 KiB
        Amount of eraseblocks:          400 (52428800 bytes, 50.0 MiB)
        Minimum input/output unit size: 2048 bytes
        Sub-page size:                  2048 bytes
        OOB size:                       64 bytes
        Character device major/minor:   90:4
        Bad blocks are allowed:         true
        Device is writable:             true

    
    I'm directly retrun 0 in the function do_sync_erase, is there any problems ?
 
Looking forward to your feedback.
Best regards,
Cai Zhiyong.

http://www.huawei.com
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