Android6.0 MountService和vold详解（三） vold SD卡、otg

既上面两篇博客，继续分析vold、对外置SD卡和OTG的分析：

一、process_config函数

上一篇我们再main函数中分析了VolumeManager的start函数，这次我们接下来分析process_config函数

static int process_config(VolumeManager *vm) {
    std::string path(android::vold::DefaultFstabPath());
    fstab = fs_mgr_read_fstab(path.c_str());
    if (!fstab) {
        PLOG(ERROR) << "Failed to open default fstab " << path;
        return -1;
    }

    /* Loop through entries looking for ones that vold manages */
    bool has_adoptable = false;
    for (int i = 0; i < fstab->num_entries; i++) {
        if (fs_mgr_is_voldmanaged(&fstab->recs[i])) {
            if (fs_mgr_is_nonremovable(&fstab->recs[i])) {
                LOG(WARNING) << "nonremovable no longer supported; ignoring volume";
                continue;
            }

            std::string sysPattern(fstab->recs[i].blk_device);
            std::string nickname(fstab->recs[i].label);
            int flags = 0;

            if (fs_mgr_is_encryptable(&fstab->recs[i])) {
                flags |= android::vold::Disk::Flags::kAdoptable;
                has_adoptable = true;
            }
            if (fs_mgr_is_noemulatedsd(&fstab->recs[i])
                    || property_get_bool("vold.debug.default_primary", false)) {
                flags |= android::vold::Disk::Flags::kDefaultPrimary;
            }
	    PLOG(ERROR) << "process_config:" <<" sysPattern:" << sysPattern <<" nickname:" << nickname<<" end";
            vm->addDiskSource(std::shared_ptr<VolumeManager::DiskSource>(
                    new VolumeManager::DiskSource(sysPattern, nickname, flags)));
        }
    }
    property_set("vold.has_adoptable", has_adoptable ? "1" : "0");
    return 0;
}

process_config函数就是遍历fstab文件，下面就是fstab文件

# Android fstab file.
#<src>                                         <mnt_point>  <type>  <mnt_flags and options>  <fs_mgr_flags>
# The filesystem that contains the filesystem checker binary (typically /system) cannot
# specify MF_CHECK, and must come before any filesystems that do specify MF_CHECK

/dev/block/platform/comip-mmc.1/by-name/system                    /system          ext4    ro,barrier=1                                                    wait
/dev/block/platform/comip-mmc.1/by-name/cache                     /cache           ext4    noatime,nosuid,nodev,barrier=1,data=ordered                     wait,check
/dev/block/platform/comip-mmc.1/by-name/userdata                  /data            ext4    noatime,nosuid,nodev,barrier=1,data=ordered,noauto_da_alloc     wait,check,encryptable=footer
#/dev/block/platform/comip-mmc.1/by-name/amt                      /amt             ext4    rw                                                              wait
/devices/platform/comip-mmc.0/mmc_host/mmc1/*                       auto             vfat    defaults                                                        voldmanaged=sdcard1:auto,encryptable=false
/devices/a0400000.usb_hcd/usb1/*                                    auto      vfat    defaults        voldmanaged=usbotg:auto,noemulatedsd
/dev/block/mmcblk1p1                                              /sdcard                vfat  defaults  recoveryonly
/dev/block/platform/comip-mmc.1/by-name/kernel                                /kernel          emmc        defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk                   /boot                  emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk_recovery          /recovery        emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk_amt1              /ramdisk_amt1    emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk_amt3              /ramdisk_amt3    emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/kernel_recovery           /kernel_recovery emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/logo                      /logo            emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/misc                      /misc            emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/fota                      /fota            emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/modemarm                  /modemarm        emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/modemdsp                  /modemdsp        emmc    defaults    defaults
/dev/block/mmcblk0boot0                                           /uboot           emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/lcboot                          /lcboot          emmc    defaults    defaults
/dev/block/zram0                                                  none          swap    defaults        zramsize=268435456

简单说上面的函数就是遍历fstab文件中有voldmanaged的那项，然后新建一个DiskSource对象，加入volumeManager。

我们再来看看上面加的log的打印

01-01 09:00:25.347   164   164 E vold    :process_config: sysPattern:/devices/platform/comip-mmc.0/mmc_host/mmc1/* nickname:sdcard1 end: Success
01-01 09:00:25.347   164   164 E vold    :process_config: sysPattern:/devices/a0400000.usb_hcd/usb1/* nickname:usbotg end: Success

一个nickname是sdcard1，另一个是usbotg。

二、Disk的创建

下面我们来看下kernel对sdcard的检测到之后，通知v