On 08/10/12 07:24, Dave Chinner wrote:
> On Fri, Aug 03, 2012 at 02:10:55PM +0800, Jeff Liu wrote:
>> Introduce helpers to probe data or hole offset from page cache for unwritten extents.
> .....
>> + * Lookup the desired type of offset from the given page.
>> + *
>> + * On success, return true and the offset argument will point to the
>> + * searched offset. Otherwise this function will return false and
> I'm not sure what the "searched offset" is. Is it the start of the
> data or hole region that has been found?
Yes, it is.
> If so, it woul dbe clearer
> to write:
>
> * On success, return true and the offset argument will point to the
> * start of the region that was found. Otherwise this function will return false and
I'll fix the comments for it.
>
>> + * keep the offset argument unchanged.
>> + */
>> +STATIC bool
>> +xfs_lookup_buffer_offset(
>> + struct page *page,
>> + loff_t *offset,
>> + unsigned int type)
>> +{
>> + loff_t lastoff = page_offset(page);
>> + bool found = false;
>> + struct buffer_head *bh, *head;
>> +
>> + bh = head = page_buffers(page);
>> + do {
>> + /*
>> + * Unwritten extents that have data in the page
>> + * cache covering them can be identified by the
>> + * BH_Unwritten state flag. Pages with multiple
>> + * buffers might have a mix of holes, data and
>> + * unwritten extents - any buffer with valid
>> + * data in it should have BH_Uptodate flag set
>> + * on it.
>> + */
>> + if (buffer_unwritten(bh) ||
>> + buffer_uptodate(bh)) {
>> + if (type == DATA_OFF)
>> + found = true;
>> + } else {
>> + if (type == HOLE_OFF)
>> + found = true;
>> + }
>> +
>> + if (found) {
>> + *offset = lastoff;
>> + unlock_page(page);
>> + break;
> You don't lock the page in this function, so you shouldn't unlock
> it, either. Let the caller handle that.
>
>> + }
>> + lastoff += bh->b_size;
>> + } while ((bh = bh->b_this_page) != head);
>> +
>> + return found;
>> +}
>> +
>> +/*
>> + * This routine is called to find out and return a data or hole offset
>> + * from the page cache for unwritten extents according to the desired
>> + * type for xfs_seek_data() or xfs_seek_hole().
>> + *
>> + * The argument offset is used to tell where we start to search from the
>> + * page cache. Map is used to figure out the end points of the range to
>> + * lookup pages.
>> + *
>> + * Return true if the desired type of offset was found, and the argument
>> + * offset is filled with that address. Otherwise, return false and keep
>> + * offset unchanged.
>> + */
>> +STATIC bool
>> +xfs_find_get_desired_pgoff(
>> + struct inode *inode,
>> + struct xfs_bmbt_irec *map,
>> + unsigned int type,
>> + loff_t *offset)
>> +{
>> + struct xfs_inode *ip = XFS_I(inode);
>> + struct xfs_mount *mp = ip->i_mount;
>> + struct pagevec pvec;
>> + pgoff_t index;
>> + pgoff_t end;
>> + loff_t endoff;
>> + loff_t startoff = *offset;
>> + loff_t lastoff = startoff;
>> + bool found = false;
>> +
>> + pagevec_init(&pvec, 0);
>> +
>> + index = startoff >> PAGE_CACHE_SHIFT;
>> + endoff = XFS_FSB_TO_B(mp, map->br_startoff + map->br_blockcount);
>> + end = endoff >> PAGE_CACHE_SHIFT;
>> + do {
>> + int want;
>> + unsigned nr_pages;
>> + unsigned int i;
>> +
>> + want = min_t(pgoff_t, end - index, (pgoff_t)PAGEVEC_SIZE);
>> + nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index,
>> + want);
>> + /*
>> + * No page mapped into given range. If we are searching holes
>> + * and if this is the first time we got into the loop, it means
>> + * that the given offset is landed in a hole, return it.
>> + *
>> + * If we have already stepped through some block buffers to find
>> + * holes but they all contains data. In this case, the last
>> + * offset is already updated and pointed to the end of the last
>> + * mapped page, if it does not reach the endpoint to search,
>> + * that means there should be a hole between them.
>> + */
>> + if (nr_pages == 0) {
>> + /* Data search found nothing */
>> + if (type == DATA_OFF)
>> + break;
>> +
>> + ASSERT(type == HOLE_OFF);
>> + if (lastoff == startoff || lastoff < endoff) {
>> + found = true;
>> + *offset = lastoff;
>> + }
>> + break;
>> + }
>> +
>> + /*
>> + * At lease we found one page. If this is the first time we
>> + * step into the loop, and if the first page index offset is
>> + * greater than the given search offset, a hole was found.
>> + */
>> + if (type == HOLE_OFF && lastoff == startoff &&
>> + lastoff < page_offset(pvec.pages[0])) {
>> + found = true;
>> + break;
>> + }
>> +
>> + for (i = 0; i < nr_pages; i++) {
>> + struct page *page = pvec.pages[i];
>> + loff_t b_offset;
>> +
>> + /*
>> + * Page index is out of range, searching done.
>> + * If the current offset is not reaches the end
>> + * of the specified search range, there should
>> + * be a hole between them.
>> + */
>> + if (page->index > end) {
>> + if (type == HOLE_OFF && lastoff < endoff) {
>> + *offset = lastoff;
>> + found = true;
>> + }
>> + goto out;
>> + }
>> +
>> + lock_page(page);
>> + /*
>> + * Page truncated or invalidated(page->mapping == NULL).
>> + * We can freely skip it and proceed to check the next
>> + * page.
>> + */
>> + if (unlikely(page->mapping != inode->i_mapping)) {
>> + unlock_page(page);
>> + continue;
>> + }
>> +
>> + if (!page_has_buffers(page)) {
>> + unlock_page(page);
>> + continue;
>> + }
>> +
>> + found = xfs_lookup_buffer_offset(page, &b_offset, type);
>> + if (found) {
>> + /*
>> + * The found offset may be less than the start
>> + * point to search if this is the first time to
>> + * come here.
>> + */
>> + *offset = max_t(loff_t, startoff, b_offset);
> You should unlock the page here.
exactly.
>
>> + goto out;
>> + }
>> +
>> + /*
>> + * We either searching data but nothing was found, or
>> + * searching hole but found a data buffer. In either
>> + * case, probably the next page contains the desired
>> + * things, update the last offset to it so.
>> + */
>> + lastoff = page_offset(page) + PAGE_SIZE;
>> + unlock_page(page);
>> + }
>> +
>> + /*
>> + * The number of returned pages less than our desired, search
>> + * done. In this case, nothing was found for searching data,
>> + * but we found a hole behind the last offset.
>> + */
>> + if (nr_pages < want) {
>> + if (type == HOLE_OFF) {
>> + *offset = lastoff;
>> + found = true;
>> + }
>> + break;
>> + }
>> +
>> + index = pvec.pages[i - 1]->index + 1;
> You have to sample the index while the page is locked, otherwise it
> can be invalid. Hence you have to update index every time through
> the above page array loop.
I'll take care of it, thanks!
-Jeff
>
> Other than that, it looks fine.
>
> Cheers,
>
> Dave.
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