ext4 ext4_mount

ext4_mount

ext4 挂载函数，由具体的文件系统提供

static struct dentry *ext4_mount(struct file_system_type *fs_type, int flags,
		       const char *dev_name, void *data)
{
	return mount_bdev(fs_type, flags, dev_name, data, ext4_fill_super);
}

struct dentry *mount_bdev(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data,
	int (*fill_super)(struct super_block *, void *, int))
{
	struct block_device *bdev;
	struct super_block *s;
	fmode_t mode = FMODE_READ | FMODE_EXCL;
	int error = 0;


	if (!(flags & MS_RDONLY))
		mode |= FMODE_WRITE;

	获取设备
	bdev = blkdev_get_by_path(dev_name, mode, fs_type);
	if (IS_ERR(bdev))
		return ERR_CAST(bdev);


	/*
	 * once the super is inserted into the list by sget, s_umount
	 * will protect the lockfs code from trying to start a snapshot
	 * while we are mounting
	 */
	mutex_lock(&bdev->bd_fsfreeze_mutex);
	if (bdev->bd_fsfreeze_count > 0) {
		mutex_unlock(&bdev->bd_fsfreeze_mutex);
		error = -EBUSY;
		goto error_bdev;
	}
	s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
		
	mutex_unlock(&bdev->bd_fsfreeze_mutex);
	if (IS_ERR(s))
		goto error_s;


	if (s->s_root) {
		if ((flags ^ s->s_flags) & MS_RDONLY) {
			deactivate_locked_super(s);
			error = -EBUSY;
			goto error_bdev;
		}


		/*
		 * s_umount nests inside bd_mutex during
		 * __invalidate_device().  blkdev_put() acquires
		 * bd_mutex and can't be called under s_umount.  Drop
		 * s_umount temporarily.  This is safe as we're
		 * holding an active reference.
		 */
		up_write(&s->s_umount);
		blkdev_put(bdev, mode);
		down_write(&s->s_umount);
	} else {
		s->s_mode = mode;
		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
		sb_set_blocksize(s, block_size(bdev));
		error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
		if (error) {
			deactivate_locked_super(s);
			goto error;
		}


		s->s_flags |= MS_ACTIVE;
		bdev->bd_super = s;
	}


	return dget(s->s_root);


error_s:
	error = PTR_ERR(s);
error_bdev:
	blkdev_put(bdev, mode);
error:
	return ERR_PTR(error);
}