Re: [PATCH 10/13: eCryptfs] Mmap operations

["Pekka Enberg" <penberg@cs.helsinki.fi>]

On 5/4/06, Phillip Hellewell <phillip@hellewell.homeip.net> wrote:
> +/**
> + * Get one page from cache or lower f/s, return error otherwise.
> + *
> + * @return Unlocked and up-to-date page (if ok), with increased
> + *         refcnt.
> + */
> +static struct page *ecryptfs_get1page(struct file *file, int index)
> +{
> +       struct page *page;
> +       struct dentry *dentry;
> +       struct inode *inode;
> +       struct address_space *mapping;
> +       int rc;
> +
> +       ecryptfs_printk(KERN_DEBUG, "Enter\n");
> +       dentry = file->f_dentry;
> +       inode = dentry->d_inode;
> +       mapping = inode->i_mapping;
> +       page = read_cache_page(mapping, index,
> +                              (filler_t *)mapping->a_ops->readpage,
> +                              (void *)file);
> +       if (IS_ERR(page))
> +               goto out;
> +       wait_on_page_locked(page);
> +       if (!PageUptodate(page)) {
> +               lock_page(page);
> +               rc = mapping->a_ops->readpage(file, page);

What's the purpose of this second read?

> +               if (rc) {
> +                       page = ERR_PTR(rc);
> +                       goto out;
> +               }
> +               wait_on_page_locked(page);
> +               if (!PageUptodate(page)) {
> +                       page = ERR_PTR(-EIO);
> +                       goto out;
> +               }
> +       }
> +out:
> +       ecryptfs_printk(KERN_DEBUG, "Exit\n");
> +       return page;
> +}

[snip]

> +/**
> + * Reads the data from the lower file file at index lower_page_index
> + * and copies that data into page.
> + *
> + * @param page Page to fill
> + * @param lower_page_index Index of the page in the lower file to get
> + */
> +int ecryptfs_do_readpage(struct file *file, struct page *page,
> +                        pgoff_t lower_page_index)
> +{
> +       int rc = -EIO;
> +       struct dentry *dentry;
> +       struct file *lower_file;
> +       struct dentry *lower_dentry;
> +       struct inode *inode;
> +       struct inode *lower_inode;
> +       char *page_data;
> +       struct page *lower_page = NULL;
> +       char *lower_page_data;
> +       struct address_space_operations *lower_a_ops;
> +
> +       ecryptfs_printk(KERN_DEBUG, "Enter; lower_page_index = [0x%.16x]\n",
> +                       lower_page_index);
> +       dentry = file->f_dentry;
> +       if (NULL == ECRYPTFS_FILE_TO_PRIVATE_SM(file)) {
> +               rc = -ENOENT;
> +               ecryptfs_printk(KERN_ERR, "No lower file info\n");
> +               goto out;
> +       }
> +       lower_file = ECRYPTFS_FILE_TO_LOWER(file);
> +       lower_dentry = ECRYPTFS_DENTRY_TO_LOWER(dentry);
> +       inode = dentry->d_inode;
> +       lower_inode = ECRYPTFS_INODE_TO_LOWER(inode);
> +       lower_a_ops = lower_inode->i_mapping->a_ops;
> +       lower_page = read_cache_page(lower_inode->i_mapping, lower_page_index,
> +                                    (filler_t *)lower_a_ops->readpage,
> +                                    (void *)lower_file);
> +       if (IS_ERR(lower_page)) {
> +               rc = PTR_ERR(lower_page);
> +               lower_page = NULL;
> +               ecryptfs_printk(KERN_ERR, "Error reading from page cache\n");
> +               goto out;
> +       }
> +       wait_on_page_locked(lower_page);
> +       if (!PageUptodate(lower_page)) {

And here?

> +               lock_page(lower_page);
> +               rc = lower_a_ops->readpage(lower_file, lower_page);
> +               if (rc) {
> +                       lower_page = NULL;
> +                       rc = -EIO;
> +                       ecryptfs_printk(KERN_ERR, "Error reading lower "
> +                                       "page at index=[0x%.16x]\n",
> +                                       lower_page_index);
> +                       goto out;
> +               }
> +               wait_on_page_locked(lower_page);
> +               if (!PageUptodate(lower_page)) {
> +                       rc = -EIO;
> +                       ecryptfs_printk(KERN_ERR, "Error reading lower "
> +                                       "page at index=[0x%.16x]\n",
> +                                       lower_page_index);
> +                       goto out;
> +               }
> +       }