概念

sysfs 是 Linux 提供的一种虚拟文件系统，他以一种层次的方式组织数据，向用户空间提供内核中的信息，让用户可以通过文件系统接口访问和操作内核对象的属性.

他提供了一种统一管理的接口，通常在 /sys 目录下挂载.

  • /sys/class: 包含了设备类别的子目录.

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    jvle@jvle-ThinkPad-X1-Carbon-Gen-8:~/Desktop/works/temp/linux_files/modules/kobjs$ ls /sys/class/
    accel       bsg            drm                  hwmon          lirc      nd              platform-profile  pwm           scsi_device   tpm                 vc
    ata_device  devcoredump    drm_dp_aux_dev       i2c-dev        mdio_bus  net             powercap          rapidio_port  scsi_disk     tpmrm               video4linux
    ata_link    devfreq        extcon               ieee80211      mei       nvme            power_supply      rc            scsi_generic  tty                 virtio-ports
    ata_port    devfreq-event  firmware             input          mem       nvme-generic    ppdev             regulator     scsi_host     typec               vtconsole
    backlight   devlink        firmware-attributes  intel_pmt      misc      nvme-subsystem  ppp               remoteproc    sound         typec_mux           wakeup
    bdi         dma            gpio                 intel_scu_ipc  mmc_host  pci_bus         pps               retimer       spi_master    usbmisc             watchdog
    block       dma_heap       graphics             iommu          msr       pci_epc         printer           rfkill        spi_slave     usb_power_delivery  wmi_bus
    bluetooth   dmi            hidraw               leds           mtd       phy             ptp               rtc           thermal       usb_role

  • /sys/devices: 包含了系统中所有设备的子目录

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    jvle@jvle-ThinkPad-X1-Carbon-Gen-8:~/Desktop/works/temp/linux_files/modules/kobjs$ ls /sys/devices/
    breakpoint  cstate_core  faux  intel_bts  isa     LNXSYSTM:00  pci0000:00  pnp0   software  tracepoint  uncore_cbox_0  uncore_cbox_2  uncore_imc  virtual
    cpu         cstate_pkg   i915  intel_pt   kprobe  msr          platform    power  system    uncore_arb  uncore_cbox_1  uncore_cbox_3  uprobe

  • /sys/bus: 包含了总线类型的子目录

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    jvle@jvle-ThinkPad-X1-Carbon-Gen-8:~/Desktop/works/temp/linux_files/modules/kobjs$ ls /sys/bus/
    ac97       clockevents  dax           gpio     isa           mei             mmc    parport      platform  sdio         snd_seq    thunderbolt  vme        xen-backend
    acpi       clocksource  edac          hdaudio  machinecheck  memory          nd     pci          pnp       serial       soc        typec        wmi
    auxiliary  container    event_source  hid      mdio_bus      memory_tiering  node   pci-epf      rapidio   serial-base  soundwire  usb          workqueue
    cec        cpu          faux          i2c      media         mipi-dsi        nvmem  pci_express  scsi      serio        spi        virtio       xen

现在要设置 gpio，我们可以通过 /sys/class 或者 /sys/devices 来控制.

通常来说，kobj 被嵌入在各个结构体中，比如 platform, device…, 因此我们可以把这些结构体看作是 kobj 的派生类.