On Wed, 2007-04-04 at 15:10 -0700, Mark Fasheh wrote:
...
> +int pagecache_write_begin(struct file *file, struct address_space *mapping,
> + loff_t pos, unsigned len, unsigned flags,
> + struct page **pagep, void **fsdata)
> +{
> + const struct address_space_operations *aops = mapping->a_ops;
> +
> + if (aops->write_begin) {
> + return aops->write_begin(file, mapping, pos, len, flags,
> + pagep, fsdata);
> + } else {
> + int ret;
> + pgoff_t index = pos >> PAGE_CACHE_SHIFT;
> + unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
> + struct inode *inode = mapping->host;
> + struct page *page;
> +again:
> + page = __grab_cache_page(mapping, index);
> + *pagep = page;
> + if (!page)
> + return -ENOMEM;
> +
> + if (flags & AOP_FLAG_UNINTERRUPTIBLE && !PageUptodate(page)) {
> + /*
> + * There is no way to resolve a short write situation
> + * for a !Uptodate page (except by double copying in
> + * the caller done by generic_perform_write_2copy).
> + *
> + * Instead, we have to bring it uptodate here.
> + */
> + ret = aops->readpage(file, page);
> + page_cache_release(page);
> + if (ret) {
> + if (ret == AOP_TRUNCATED_PAGE)
> + goto again;
> + return ret;
> + }
> + goto again;
> + }
> +
> + ret = aops->prepare_write(file, page, offset, offset+len);
> + if (ret) {
> + if (ret != AOP_TRUNCATED_PAGE)
> + unlock_page(page);
> + page_cache_release(page);
> + if (pos + len > inode->i_size)
> + vmtruncate(inode, inode->i_size);
> + if (ret == AOP_TRUNCATED_PAGE)
> + goto again;
> + }
> + return ret;
> + }
Hmm.. Okay, only filesystems that could return AOP_TRUNCATED_PAGE
are ocf2 and gfs2. Now that both of them are switched to have
write_begin()/write_end(), why do we need this code to handle
AOP_TRUNCATED_PAGE (in the else part) ? Can't we just cleanup/nuke
all the AOP_TRUNCATED_PAGE handling ?
Dumb question ?
Thanks,
Badari
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