android /system/vold源码分析(7)

process_config()分析：

process_config函数用来解析/ fstab.xxx的配置文件.

这个函数还初始化了VolumeManage和DirectVolume。
有关VolumeManage的初始化基本是这个函数内进行，除此函数，VolumeManage的初始化工作做得很少。
process_config()的代码如下：

static int process_config(VolumeManager *vm)
{
    char fstab_filename[PROPERTY_VALUE_MAX + sizeof(FSTAB_PREFIX)];
    char propbuf[PROPERTY_VALUE_MAX];
    int i;
    int ret = -1;
    int flags;

    property_get("ro.hardware", propbuf, "");
    snprintf(fstab_filename, sizeof(fstab_filename), FSTAB_PREFIX"%s", propbuf);

    fstab = fs_mgr_read_fstab(fstab_filename);
    if (!fstab) {
        SLOGE("failed to open %s\n", fstab_filename);
        return -1;
    }

    /* Loop through entries looking for ones that vold manages */
    for (i = 0; i < fstab->num_entries; i++) {
        if (fs_mgr_is_voldmanaged(&fstab->recs[i])) {
            DirectVolume *dv = NULL;
            flags = 0;

            /* Set any flags that might be set for this volume */
            if (fs_mgr_is_nonremovable(&fstab->recs[i])) {
                flags |= VOL_NONREMOVABLE;
            }
            if (fs_mgr_is_encryptable(&fstab->recs[i])) {
                flags |= VOL_ENCRYPTABLE;
            }
            /* Only set this flag if there is not an emulated sd card */
            if (fs_mgr_is_noemulatedsd(&fstab->recs[i]) &&
                !strcmp(fstab->recs[i].fs_type, "vfat")) {
                flags |= VOL_PROVIDES_ASEC;
            }
            dv = new DirectVolume(vm, &(fstab->recs[i]), flags);

            if (dv->addPath(fstab->recs[i].blk_device)) {
                SLOGE("Failed to add devpath %s to volume %s",
                      fstab->recs[i].blk_device, fstab->recs[i].label);
                goto out_fail;
            }

            vm->addVolume(dv);
        }
    }

    ret = 0;

out_fail:
    return ret;
}

/fstab.xxx文件格式为：
<src> <mnt_point> <type> <mnt_flags and options> <fs_mgr_flags>
例如：

/dev/block/platform/dw_mmc.2/by-num/p2  /system  ext4  ro  wait
/dev/block/platform/dw_mmc.2/by-num/p3 /cache ext4   noatime,nosuid,nodev,nomblk_io_submit,errors=panic    wait,check
/dev/block/platform/dw_mmc.2/by-num/p4 /data  ext4   noatime,nosuid,nodev,nomblk_io_submit,errors=panic    wait,check
/devices/platform/dw_mmc.0/mmc_host/mmc0/mmc0  /storage/sdcard1 auto defaults  voldmanaged=sdcard1:auto,noemulatedsd

fs_mgr_read_fstab(fstab_filename);的作用即是解析fstab文件的每行并返回fstab结构体：

struct fstab {
    int num_entries;   //fstab文件中每行（除空行和注释外）解析出一个fstab_rec结构体。
    struct fstab_rec *recs;
    char *fstab_filename;  //即fstab文件名
};

struct fstab_rec {
    char *blk_device;
    char *mount_point;
    char *fs_type;
    unsigned long flags;
    char *fs_options;
    int fs_mgr_flags;
    char *key_loc;
    char *verity_loc;
    long long length;
    char *label;
    int partnum;
    int swap_prio;
    unsigned int zram_size;
};

下面的代码根据每个fstab_rec生成一个DirectVolume类， 并执行：
vm->addVolume(dv);
即对VolumeManager做了初始化工作。注意DirectVolume是Volume的子类。

分析一些多余的代码，当NetlinkHandler接收到来自block子系统的uevent时：

void NetlinkHandler::onEvent(NetlinkEvent *evt) {
    VolumeManager *vm = VolumeManager::Instance();
    const char *subsys = evt->getSubsystem();

    if (!subsys) {
        SLOGW("No subsystem found in netlink event");
        return;
    }

    if (!strcmp(subsys, "block")) {
        vm->handleBlockEvent(evt);
    }
}

执行VolumeManager:: handleBlockEvent(evt):

void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
    const char *devpath = evt->findParam("DEVPATH");

    /* Lookup a volume to handle this device */
    VolumeCollection::iterator it;
    bool hit = false;
    for (it = mVolumes->begin(); it != mVolumes->end(); ++it) {
        if (!(*it)->handleBlockEvent(evt)) {
#ifdef NETLINK_DEBUG
            SLOGD("Device '%s' event handled by volume %s\n", devpath, (*it)->getLabel());
#endif
            hit = true;
            break;
        }
    }

    if (!hit) {
#ifdef NETLINK_DEBUG
        SLOGW("No volumes handled block event for '%s'", devpath);
#endif
    }
}

在VolumeManager::handleBlockEvent遍历所有Volume，并执行Volume:: handleBlockEvent()，实际上是跳转到了DirectVolume::handleBlockEvent。为什么是这里，前面已经说过，DirectVolume是Volume的子类。