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    SubjectRe: [PATCH] 2.6.14 patch for supporting madvise(MADV_REMOVE)
    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.
    -
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