xfs: Introduce a helper routine to probe data or hole offset from page cache

Introduce helpers to probe data or hole offset from page cache.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 219 insertions, 0 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 92ba18f841f1..d78a746b6c7c 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -36,6 +36,7 @@
 
 #include <linux/dcache.h>
 #include <linux/falloc.h>
+#include <linux/pagevec.h>
 
 static const struct vm_operations_struct xfs_file_vm_ops;
 
@@ -959,6 +960,224 @@ xfs_vm_page_mkwrite(
         return block_page_mkwrite(vma, vmf, xfs_get_blocks);
 }
 
+/*
+ * This type is designed to indicate the type of offset we would like
+ * to search from page cache for either xfs_seek_data() or xfs_seek_hole().
+ */
+enum {
+        HOLE_OFF = 0,
+        DATA_OFF,
+};
+
+/*
+ * Lookup the desired type of offset from the given page.
+ *
+ * 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 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;
+                        break;
+                }
+                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, 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;
+
+                        /*
+                         * At this point, the page may be truncated or
+                         * invalidated (changing page->mapping to NULL),
+                         * or even swizzled back from swapper_space to tmpfs
+                         * file mapping. However, page->index will not change
+                         * because we have a reference on the page.
+                         *
+                         * Searching done if the page index is out of range.
+                         * 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);
+                                unlock_page(page);
+                                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;
+                pagevec_release(&pvec);
+        } while (index <= end);
+
+out:
+        pagevec_release(&pvec);
+        return found;
+}
+
 STATIC loff_t
 xfs_seek_data(
         struct file             *file,