Introduce helpers to probe data or hole offset from page cache.
Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
---
fs/xfs/xfs_file.c | 219 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 219 insertions(+), 0 deletions(-)
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 92ba18f..d78a746 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,
--
1.7.4.1
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