vfs_kern_mount

在sys_mount的调用过程中，会调用到vfs_kern_mount
调用关系如下：
sys_mount  
    ->do_mount
        ->do_new_mount
           ->do_kern_mount
                ->vfs_kern_mount

在proc_fs中也会调用vfs_kern_mount

void __init proc_root_init(void)
{
    ...
    proc_mnt = kern_mount_data(&proc_fs_type, &init_pid_ns);
    ...
}

struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
{
    return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
}

struct vfsmount *
do_kern_mount(const char *fstype, int flags, const char *name, void *data)
{
    struct file_system_type *type = get_fs_type(fstype);
    struct vfsmount *mnt;
    if (!type)
        return ERR_PTR(-ENODEV);
    mnt = vfs_kern_mount(type, flags, name, data);
    if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
     !mnt->mnt_sb->s_subtype)
        mnt = fs_set_subtype(mnt, fstype);
    put_filesystem(type);
    return mnt;
}

struct vfsmount *
vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
{
    struct vfsmount *mnt;
    char *secdata = NULL;
    int error;

    if (!type)
        return ERR_PTR(-ENODEV);
    /* 分配一份vfsmount结构 */
    error = -ENOMEM;
    mnt = alloc_vfsmnt(name);
    if (!mnt)
        goto out;

    if (flags & MS_KERNMOUNT)
        mnt->mnt_flags = MNT_INTERNAL;

    if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
        secdata = alloc_secdata();
        if (!secdata)
            goto out_mnt;

        error = security_sb_copy_data(data, secdata);
        if (error)
            goto out_free_secdata;
    }
    /* 读取超级块
       procfs对应的函数是proc_get_sb
     */
    error = type->get_sb(type, flags, name, data, mnt);
    if (error < 0)
        goto out_free_secdata;
    BUG_ON(!mnt->mnt_sb);
    WARN_ON(!mnt->mnt_sb->s_bdi);
    WARN_ON(mnt->mnt_sb->s_bdi == &default_backing_dev_info);
    mnt->mnt_sb->s_flags |= MS_BORN;

    error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
    if (error)
        goto out_sb;

    /*
     * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
     * but s_maxbytes was an unsigned long long for many releases. Throw
     * this warning for a little while to try and catch filesystems that
     * violate this rule. This warning should be either removed or
     * converted to a BUG() in 2.6.34.
     */
    WARN((mnt->mnt_sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
        "negative value (%lld)\n", type->name, mnt->mnt_sb->s_maxbytes);

    mnt->mnt_mountpoint = mnt->mnt_root;
    mnt->mnt_parent = mnt;
    up_write(&mnt->mnt_sb->s_umount);
    free_secdata(secdata);
    return mnt;
out_sb:
    dput(mnt->mnt_root);
    deactivate_locked_super(mnt->mnt_sb);
out_free_secdata:
    free_secdata(secdata);
out_mnt:
    free_vfsmnt(mnt);
out:
    return ERR_PTR(error);
}