How to free data block of ext2 fs?

Hi all ,
I wanted to free a data block from disk. So I made a loop device for ext2 fs
and inserted my module(code) through insmod command.

Here are the details :
 I found a function named ext2_free_data() which takes block numbers to be
freed as a parameter. The declaration of the function is as follows :

void ext2_free_data(struct inode *inode, __le32 *p, __le32 *q);

As we can see this function use structure of inode object and it make
changes in this inode object.

This function changes the fields in in-core inode and mark the inode dirty.
But I want the changes made in in-core inode to be reflected in disk
inode immediately .


Is there any command to flush the buffers ?



-- 
Regards,
Kashish
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