Re: [PATCH] 2.6.14 patch for supporting madvise(MADV_REMOVE)

[Andrew Morton <akpm@osdl.org>]

Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
> +int vmtruncate_range(struct inode * inode, loff_t offset, loff_t end)
>  +{
>  +	struct address_space *mapping = inode->i_mapping;
>  +
>  +	/*
>  +	 * If the underlying filesystem is not going to provide 
>  +	 * a way to truncate a range of blocks (punch a hole) - 
>  +	 * we should return failure right now.
>  +	 */
>  +	if (!inode->i_op || !inode->i_op->truncate_range)
>  +		return -ENOSYS;
>  +		
>  +	/* XXX - Do we need both i_sem and i_allocsem all the way ? */
>  +	down(&inode->i_sem);
>  +	down_write(&inode->i_alloc_sem);
>  +	unmap_mapping_range(mapping, offset, (end - offset), 1);
>  +	truncate_inode_pages_range(mapping, offset, end);
>  +	inode->i_op->truncate_range(inode, offset, end);
>  +	up_write(&inode->i_alloc_sem);
>  +	up(&inode->i_sem);
>  +
>  +	return 0;
>  +}

Yes, we need to take i_alloc_sem for writing.  To prevent concurrent
direct-io reads from coming in and instantiated by unwritten blocks.

tmpfs doesn't implements direct-io though.