Linux Kernel（10.3.1）- Command line partition table parsing for Kernel 4.19

由於10.3的kernel過時，所以10.3.1是用kernel 4.19來做補充。
MTD Partition除了在code中寫死以外，其實還可以透過一些parsers來作規劃，這一章就要來教大家如何使用"Command line partition table parsing"。
首先必須在kernel中啟用"Command line partition table parsing"，請參照10.3。
接著在command line中加入mtdparts的設定，其簡單說明如下:

 * mtdparts=<mtddef>[;<mtddef]
 * <mtddef>  := <mtd-id>:<partdef>[,<partdef>]
 * <partdef> := <size>[@<offset>][<name>][ro][lk]
 * <mtd-id>  := unique name used in mapping driver/device (mtd->name)
 * <size>    := standard linux memsize OR "-" to denote all remaining space
 *              size is automatically truncated at end of device
 *              if specified or truncated size is 0 the part is skipped
 * <offset>  := standard linux memsize
 *              if omitted the part will immediately follow the previous part
 *              or 0 if the first part
 * <name>    := '(' NAME ')'
 *              NAME will appear in /proc/mtd
 *
 * <size> and <offset> can be specified such that the parts are out of order
 * in physical memory and may even overlap.
 *
 * The parts are assigned MTD numbers in the order they are specified in the
 * command line regardless of their order in physical memory.

 * Due to the way Linux handles the command line, no spaces are
 * allowed in the partition definition, including mtd id's and partition
 * names.

這裡我用qemu與mtdram來執行，執行參數如下

qemu-system-arm -s -M vexpress-a9 -m 128M -kernel ./linux/arch/arm/boot/zImage \
                -dtb ./linux/arch/arm/boot/dts/vexpress-v2p-ca9.dtb -initrd ./initrd-arm.img \
                -nographic -append "console=ttyAMA0 mtdparts=\"mtdram test device:1024k(p1),1024k(p2),-(p3)\""

這裡特別要說明的是mtd-id就是mtd name，基本上你可以以cat /proc/mtd，就可以知道mtd name了，或者trace一下code也行

// file "drivers/mtd/cmdlinepart.c"
static int parse_cmdline_partitions(struct mtd_info *master,
                    const struct mtd_partition **pparts,
                    struct mtd_part_parser_data *data)
{
    ...
const char *mtd_id = master->name;
    /*
     * Search for the partition definition matching master->name.
     * If master->name is not set, stop at first partition definition.
     */
    for (part = partitions; part; part = part->next) {
        if ((!mtd_id) || (!strcmp(part->mtd_id, mtd_id)))
            break;
    }
    ...
}

// drivers/mtd/devices/mtdram.c
static int __init init_mtdram(void)
{
    ...
    err = mtdram_init_device(mtd_info, addr, MTDRAM_TOTAL_SIZE, "mtdram test device");
    ...
}

int mtdram_init_device(struct mtd_info *mtd, void *mapped_address,
        unsigned long size, const char *name)
{
    ...
    /* Setup the MTD structure */
    mtd->name = name;
    ...
}

此外我多印了一些deubg資訊在drivers/mtd/cmdlinepart.c

diff --git a/drivers/mtd/cmdlinepart.c b/drivers/mtd/cmdlinepart.c
index 3ea44cff9b75..a411ce85097e 100644
--- a/drivers/mtd/cmdlinepart.c
+++ b/drivers/mtd/cmdlinepart.c
@@ -48,6 +48,7 @@
  * edb7312-nor:256k(ARMboot)ro,-(root);edb7312-nand:-(home)
  */

+#define DEBGU
 #define pr_fmt(fmt)    "mtd: " fmt

 #include 
@@ -58,7 +59,7 @@
 #include 

 /* debug macro */
-#if 0
+#if 1
 #define dbg(x) do { printk("DEBUG-CMDLINE-PART: "); printk x; } while(0)
 #else
 #define dbg(x)
@@ -315,6 +316,7 @@ static int parse_cmdline_partitions(struct mtd_info *master,
        struct cmdline_mtd_partition *part;
        const char *mtd_id = master->name;

+       printk("BROOK, %s(#%d), cmdline_parsed:%d\n", __func__, __LINE__, cmdline_parsed);
        /* parse command line */
        if (!cmdline_parsed) {
                err = mtdpart_setup_real(cmdline);
@@ -327,12 +329,15 @@ static int parse_cmdline_partitions(struct mtd_info *master,
         * If master->name is not set, stop at first partition definition.
         */
        for (part = partitions; part; part = part->next) {
+           printk("BROOK, %s(#%d), mtd_id:%s, part->mtd_id:%s\n", __func__, __LINE__, mtd_id, part->mtd_id);
                if ((!mtd_id) || (!strcmp(part->mtd_id, mtd_id)))
                        break;
        }

-       if (!part)
+       printk("BROOK, %s(#%d), part:%p\n", __func__, __LINE__, part);
+       if (!part) {
                return 0;
+       }

        for (i = 0, offset = 0; i < part->num_parts; i++) {
                if (part->parts[i].offset == OFFSET_CONTINUOUS)

執行結果如下:

/ # dmesg
...
[    4.688086] BROOK, parse_cmdline_partitions(#319), cmdline_parsed:0
[    4.688876] DEBUG-CMDLINE-PART:
[    4.688994] parsing <1024k(p1),1024k(p2),-(p3)>
[    4.690787] DEBUG-CMDLINE-PART:
[    4.690944] partition 2: name <p3>, offset ffffffffffffffff, size ffffffffffffffff, mask flags 0
[    4.692017] DEBUG-CMDLINE-PART:
[    4.692102] partition 1: name <p2>, offset ffffffffffffffff, size 100000, mask flags 0
[    4.692950] DEBUG-CMDLINE-PART:
[    4.693034] partition 0: name <p1>, offset ffffffffffffffff, size 100000, mask flags 0
[    4.693993] DEBUG-CMDLINE-PART:
[    4.694101] mtdid=<mtdram test device> num_parts=<3>
[    4.695000] BROOK, parse_cmdline_partitions(#332), mtd_id:40000000.flash, part->mtd_id:mtdram test device
[    4.696546] BROOK, parse_cmdline_partitions(#337), part:  (null)
[    4.763129] BROOK, parse_cmdline_partitions(#319), cmdline_parsed:1
[    4.763742] BROOK, parse_cmdline_partitions(#332), mtd_id:48000000.psram, part->mtd_id:mtdram test device
[    4.764461] BROOK, parse_cmdline_partitions(#337), part:  (null)
[    4.806551] BROOK, parse_cmdline_partitions(#319), cmdline_parsed:1
[    4.808150] BROOK, parse_cmdline_partitions(#332), mtd_id:mtdram test device, part->mtd_id:mtdram test device
[    4.809227] BROOK, parse_cmdline_partitions(#337), part:(ptrval)
[    4.810325] 3 cmdlinepart partitions found on MTD device mtdram test device
[    4.811006] Creating 3 MTD partitions on "mtdram test device":
[    4.813103] 0x000000000000-0x000000100000 : "p1"
[    4.830841] 0x000000100000-0x000000200000 : "p2"
[    4.846502] 0x000000200000-0x000000400000 : "p3"
...

/ # cat /proc/mtd
dev:    size   erasesize  name
mtd0: 08000000 00040000 "40000000.flash"
mtd1: 02000000 00001000 "48000000.psram"
mtd2: 00100000 00020000 "p1"
mtd3: 00100000 00020000 "p2"
mtd4: 00200000 00020000 "p3"

/ # zcat /proc/config.gz | grep -i MTDRAM
CONFIG_MTD_MTDRAM=y
CONFIG_MTDRAM_TOTAL_SIZE=4096
CONFIG_MTDRAM_ERASE_SIZE=128