linux – 内核在哪里定义SD卡命名索引？

我正在运行一个从SDCard启动的嵌入式主板. rootfs的位置通过内核参数传递给内核：

Kernel command line: console=ttyS0,115200 root=/dev/mmcblk0p2 rootwait panic=10

我注意到更改为不同的内核版本会将索引更改为mmcblk1,从而导致设备无法启动.

内核是在没有initramfs的情况下构建的.

两个版本的udevadm输出：

mmcblk1

$udevadm info --name=/dev/mmcblk1 --attribute-walk
  looking at device '/devices/platform/soc/1c0f000.mmc/mmc_host/mmc1/mmc1:0001/block/mmcblk1':
    KERNEL=="mmcblk1"
    SUBSYstem=="block"
    DRIVER==""
    ATTR{alignment_offset}=="0"
    ATTR{capability}=="50"
    ATTR{discard_alignment}=="0"
    ATTR{ext_range}=="256"
    ATTR{force_ro}=="0"
    ATTR{inflight}=="       0        0"
    ATTR{range}=="8"
    ATTR{removable}=="0"
    ATTR{ro}=="0"
    ATTR{size}=="7716864"
    ATTR{stat}=="    2203     1698   122077    22625      654      554    26088     8770        0    12855    31530"

  looking at parent device '/devices/platform/soc/1c0f000.mmc/mmc_host/mmc1/mmc1:0001':
    KERNELS=="mmc1:0001"
    SUBSYstemS=="mmc"
    DRIVERS=="mmcblk"
    ATTRS{cid}=="9f544930303030300000000201011a3b"
    ATTRS{csd}=="400e00325b5900001d6f7f800a4000a1"
    ATTRS{date}=="10/2017"
    ATTRS{dsr}=="0x404"
    ATTRS{erase_size}=="512"
    ATTRS{fwrev}=="0x0"
    ATTRS{hwrev}=="0x0"
    ATTRS{manfid}=="0x00009f"
    ATTRS{name}=="00000"
    ATTRS{ocr}=="00200000"
    ATTRS{oemid}=="0x5449"
    ATTRS{preferred_erase_size}=="4194304"
    ATTRS{scr}=="02b5800000000000"
    ATTRS{serial}=="0x00000201"
    ATTRS{ssr}=="000000000200000004049000080a0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
    ATTRS{type}=="SD"

  looking at parent device '/devices/platform/soc/1c0f000.mmc/mmc_host/mmc1':
    KERNELS=="mmc1"
    SUBSYstemS=="mmc_host"
    DRIVERS==""

mmcblk0

~# udevadm info --name=/dev/mmcblk0 --attribute-walk
  looking at device '/devices/platform/soc/1c0f000.mmc/mmc_host/mmc0/mmc0:0001/block/mmcblk0':
    KERNEL=="mmcblk0"
    SUBSYstem=="block"
    DRIVER==""
    ATTR{alignment_offset}=="0"
    ATTR{capability}=="50"
    ATTR{discard_alignment}=="0"
    ATTR{ext_range}=="256"
    ATTR{force_ro}=="0"
    ATTR{inflight}=="       0        0"
    ATTR{range}=="8"
    ATTR{removable}=="0"
    ATTR{ro}=="0"
    ATTR{size}=="7716864"
    ATTR{stat}=="    2156     1248   105313    35020       85      263      952     1530        0     8180    36530"

  looking at parent device '/devices/platform/soc/1c0f000.mmc/mmc_host/mmc0/mmc0:0001':
    KERNELS=="mmc0:0001"
    SUBSYstemS=="mmc"
    DRIVERS=="mmcblk"
    ATTRS{cid}=="9f5449303030303000000003ba011a5d"
    ATTRS{csd}=="400e00325b5900001d6f7f800a4000a1"
    ATTRS{date}=="10/2017"
    ATTRS{dsr}=="0x404"
    ATTRS{erase_size}=="512"
    ATTRS{fwrev}=="0x0"
    ATTRS{hwrev}=="0x0"
    ATTRS{manfid}=="0x00009f"
    ATTRS{name}=="00000"
    ATTRS{ocr}=="00200000"
    ATTRS{oemid}=="0x5449"
    ATTRS{preferred_erase_size}=="4194304"
    ATTRS{scr}=="02b5800000000000"
    ATTRS{serial}=="0x000003ba"
    ATTRS{ssr}=="000000000200000004049000080a0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
    ATTRS{type}=="SD"

  looking at parent device '/devices/platform/soc/1c0f000.mmc/mmc_host/mmc0':
    KERNELS=="mmc0"
    SUBSYstemS=="mmc_host"
    DRIVERS==""

~# udevadm info --query=property --name=/dev/mmcblk0
    DEVLINKS=/dev/disk/by-id/mmc-00000_0x000003ba /dev/disk/by-path/platform-1c0f000.mmc
    DEVNAME=/dev/mmcblk0
    DEVPATH=/devices/platform/soc/1c0f000.mmc/mmc_host/mmc0/mmc0:0001/block/mmcblk0
    DEVTYPE=disk
    ID_NAME=00000
    ID_PART_TABLE_TYPE=dos
    ID_PART_TABLE_UUID=27e953fe
    ID_PATH=platform-1c0f000.mmc
    ID_PATH_TAG=platform-1c0f000_mmc
    ID_SERIAL=0x000003ba
    MAJOR=179
    MInor=0
    SUBSYstem=block
    TAGS=:systemd:
    USEC_INITIALIZED=4723799

看看/ etc / udev我发现没有明确的规则来解决mmcblk的命名问题.

# tree /etc/udev
/etc/udev
├── hwdb.bin
├── hwdb.d
├── rules.d
└── udev.conf

命名似乎与设备树有关.使用相同的zImage更改不同的设备树会产生不同的索引.

题

什么负责设置索引,是否有配置将其设置为不同的起始索引？

解决方法:

This似乎是负责理解root = / dev / mmcblk0p2的内核代码.

鉴于不存在initramfs,没有运行udev守护程序来命名设备,并且/ dev / mmcblk1在任何地方都不存在.

然后内核以某种方式将该名称转换为负责的驱动程序,函数dev_t name_to_dev_t(const char * name)：

    ...
    if (strncmp(name, "/dev/", 5) != 0) {
        unsigned maj, min, offset;
        char dummy;

        if ((sscanf(name, "%u:%u%c", &maj, &min, &dummy) == 2) ||
            (sscanf(name, "%u:%u:%u:%c", &maj, &min, &offset, &dummy) == 3)) {
            res = MKDEV(maj, min);
            if (maj != MAJOR(res) || min != MInor(res))
                goto fail;
        } else {
            res = new_decode_dev(simple_strtoul(name, &p, 16));
            if (*p)
                goto fail;
        }
        goto done;
    }

来自lkml discussion的引用指出,命名的变化可能是由设备树中的排序引起的：

Changes in device ordering can be provoked by the order in which
entries in the DT file appear, and hence the order in which the host
SD interfaces are probed by the kernel.

linux – 内核在哪里定义SD卡命名索引？

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