[PATCH 4/4] ext4: Switch to iomap for SEEK_HOLE / SEEK_DATA

[Andreas Gruenbacher <agruenba@redhat.com>]

From: Christoph Hellwig <hch@lst.de>

Switch to the iomap_seek_hole and iomap_seek_data helpers for
implementing lseek SEEK_HOLE / SEEK_DATA, and remove all the code that
isn't needed any more.

Note that with this patch, ext4 will now always depend on the iomap code
instead of only when CONFIG_DAX is enabled, and it requires adding a
call into the extent status tree for iomap_begin as well to properly
deal with delalloc extents.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[Minor fixes and cleanups by Andreas]
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/ext4/Kconfig |   1 +
 fs/ext4/ext4.h  |   3 -
 fs/ext4/file.c  | 271 +++-----------------------------------------------------
 fs/ext4/inode.c | 100 ++++++---------------
 4 files changed, 43 insertions(+), 332 deletions(-)

diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index e38039fd96ff..73b850f5659c 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -37,6 +37,7 @@ config EXT4_FS
 	select CRC16
 	select CRYPTO
 	select CRYPTO_CRC32C
+	select FS_IOMAP
 	help
 	  This is the next generation of the ext3 filesystem.
 
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 017e55942a49..f295fce7a9c8 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2515,9 +2515,6 @@ extern void ext4_da_update_reserve_space(struct inode *inode,
 					int used, int quota_claim);
 extern int ext4_issue_zeroout(struct inode *inode, ext4_lblk_t lblk,
 			      ext4_fsblk_t pblk, ext4_lblk_t len);
-extern int ext4_get_next_extent(struct inode *inode, ext4_lblk_t lblk,
-				unsigned int map_len,
-				struct extent_status *result);
 
 /* indirect.c */
 extern int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 0d7cf0cc9b87..bc7a901c8b3f 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -20,6 +20,7 @@
 
 #include <linux/time.h>
 #include <linux/fs.h>
+#include <linux/iomap.h>
 #include <linux/mount.h>
 #include <linux/path.h>
 #include <linux/dax.h>
@@ -455,256 +456,6 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 }
 
 /*
- * Here we use ext4_map_blocks() to get a block mapping for a extent-based
- * file rather than ext4_ext_walk_space() because we can introduce
- * SEEK_DATA/SEEK_HOLE for block-mapped and extent-mapped file at the same
- * function.  When extent status tree has been fully implemented, it will
- * track all extent status for a file and we can directly use it to
- * retrieve the offset for SEEK_DATA/SEEK_HOLE.
- */
-
-/*
- * When we retrieve the offset for SEEK_DATA/SEEK_HOLE, we would need to
- * lookup page cache to check whether or not there has some data between
- * [startoff, endoff] because, if this range contains an unwritten extent,
- * we determine this extent as a data or a hole according to whether the
- * page cache has data or not.
- */
-static int ext4_find_unwritten_pgoff(struct inode *inode,
-				     int whence,
-				     ext4_lblk_t end_blk,
-				     loff_t *offset)
-{
-	struct pagevec pvec;
-	unsigned int blkbits;
-	pgoff_t index;
-	pgoff_t end;
-	loff_t endoff;
-	loff_t startoff;
-	loff_t lastoff;
-	int found = 0;
-
-	blkbits = inode->i_sb->s_blocksize_bits;
-	startoff = *offset;
-	lastoff = startoff;
-	endoff = (loff_t)end_blk << blkbits;
-
-	index = startoff >> PAGE_SHIFT;
-	end = (endoff - 1) >> PAGE_SHIFT;
-
-	pagevec_init(&pvec, 0);
-	do {
-		int i, num;
-		unsigned long nr_pages;
-
-		num = min_t(pgoff_t, end - index, PAGEVEC_SIZE - 1) + 1;
-		nr_pages = pagevec_lookup(&pvec, inode->i_mapping, index,
-					  (pgoff_t)num);
-		if (nr_pages == 0)
-			break;
-
-		for (i = 0; i < nr_pages; i++) {
-			struct page *page = pvec.pages[i];
-			struct buffer_head *bh, *head;
-
-			/*
-			 * If current offset is smaller than the page offset,
-			 * there is a hole at this offset.
-			 */
-			if (whence == SEEK_HOLE && lastoff < endoff &&
-			    lastoff < page_offset(pvec.pages[i])) {
-				found = 1;
-				*offset = lastoff;
-				goto out;
-			}
-
-			if (page->index > end)
-				goto out;
-
-			lock_page(page);
-
-			if (unlikely(page->mapping != inode->i_mapping)) {
-				unlock_page(page);
-				continue;
-			}
-
-			if (!page_has_buffers(page)) {
-				unlock_page(page);
-				continue;
-			}
-
-			if (page_has_buffers(page)) {
-				lastoff = page_offset(page);
-				bh = head = page_buffers(page);
-				do {
-					if (lastoff + bh->b_size <= startoff)
-						goto next;
-					if (buffer_uptodate(bh) ||
-					    buffer_unwritten(bh)) {
-						if (whence == SEEK_DATA)
-							found = 1;
-					} else {
-						if (whence == SEEK_HOLE)
-							found = 1;
-					}
-					if (found) {
-						*offset = max_t(loff_t,
-							startoff, lastoff);
-						unlock_page(page);
-						goto out;
-					}
-next:
-					lastoff += bh->b_size;
-					bh = bh->b_this_page;
-				} while (bh != head);
-			}
-
-			lastoff = page_offset(page) + PAGE_SIZE;
-			unlock_page(page);
-		}
-
-		/* The no. of pages is less than our desired, we are done. */
-		if (nr_pages < num)
-			break;
-
-		index = pvec.pages[i - 1]->index + 1;
-		pagevec_release(&pvec);
-	} while (index <= end);
-
-	if (whence == SEEK_HOLE && lastoff < endoff) {
-		found = 1;
-		*offset = lastoff;
-	}
-out:
-	pagevec_release(&pvec);
-	return found;
-}
-
-/*
- * ext4_seek_data() retrieves the offset for SEEK_DATA.
- */
-static loff_t ext4_seek_data(struct file *file, loff_t offset, loff_t maxsize)
-{
-	struct inode *inode = file->f_mapping->host;
-	struct extent_status es;
-	ext4_lblk_t start, last, end;
-	loff_t dataoff, isize;
-	int blkbits;
-	int ret;
-
-	inode_lock(inode);
-
-	isize = i_size_read(inode);
-	if (offset >= isize) {
-		inode_unlock(inode);
-		return -ENXIO;
-	}
-
-	blkbits = inode->i_sb->s_blocksize_bits;
-	start = offset >> blkbits;
-	last = start;
-	end = isize >> blkbits;
-	dataoff = offset;
-
-	do {
-		ret = ext4_get_next_extent(inode, last, end - last + 1, &es);
-		if (ret <= 0) {
-			/* No extent found -> no data */
-			if (ret == 0)
-				ret = -ENXIO;
-			inode_unlock(inode);
-			return ret;
-		}
-
-		last = es.es_lblk;
-		if (last != start)
-			dataoff = (loff_t)last << blkbits;
-		if (!ext4_es_is_unwritten(&es))
-			break;
-
-		/*
-		 * If there is a unwritten extent at this offset,
-		 * it will be as a data or a hole according to page
-		 * cache that has data or not.
-		 */
-		if (ext4_find_unwritten_pgoff(inode, SEEK_DATA,
-					      es.es_lblk + es.es_len, &dataoff))
-			break;
-		last += es.es_len;
-		dataoff = (loff_t)last << blkbits;
-		cond_resched();
-	} while (last <= end);
-
-	inode_unlock(inode);
-
-	if (dataoff > isize)
-		return -ENXIO;
-
-	return vfs_setpos(file, dataoff, maxsize);
-}
-
-/*
- * ext4_seek_hole() retrieves the offset for SEEK_HOLE.
- */
-static loff_t ext4_seek_hole(struct file *file, loff_t offset, loff_t maxsize)
-{
-	struct inode *inode = file->f_mapping->host;
-	struct extent_status es;
-	ext4_lblk_t start, last, end;
-	loff_t holeoff, isize;
-	int blkbits;
-	int ret;
-
-	inode_lock(inode);
-
-	isize = i_size_read(inode);
-	if (offset >= isize) {
-		inode_unlock(inode);
-		return -ENXIO;
-	}
-
-	blkbits = inode->i_sb->s_blocksize_bits;
-	start = offset >> blkbits;
-	last = start;
-	end = isize >> blkbits;
-	holeoff = offset;
-
-	do {
-		ret = ext4_get_next_extent(inode, last, end - last + 1, &es);
-		if (ret < 0) {
-			inode_unlock(inode);
-			return ret;
-		}
-		/* Found a hole? */
-		if (ret == 0 || es.es_lblk > last) {
-			if (last != start)
-				holeoff = (loff_t)last << blkbits;
-			break;
-		}
-		/*
-		 * If there is a unwritten extent at this offset,
-		 * it will be as a data or a hole according to page
-		 * cache that has data or not.
-		 */
-		if (ext4_es_is_unwritten(&es) &&
-		    ext4_find_unwritten_pgoff(inode, SEEK_HOLE,
-					      last + es.es_len, &holeoff))
-			break;
-
-		last += es.es_len;
-		holeoff = (loff_t)last << blkbits;
-		cond_resched();
-	} while (last <= end);
-
-	inode_unlock(inode);
-
-	if (holeoff > isize)
-		holeoff = isize;
-
-	return vfs_setpos(file, holeoff, maxsize);
-}
-
-/*
  * ext4_llseek() handles both block-mapped and extent-mapped maxbytes values
  * by calling generic_file_llseek_size() with the appropriate maxbytes
  * value for each.
@@ -720,18 +471,24 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int whence)
 		maxbytes = inode->i_sb->s_maxbytes;
 
 	switch (whence) {
-	case SEEK_SET:
-	case SEEK_CUR:
-	case SEEK_END:
+	default:
 		return generic_file_llseek_size(file, offset, whence,
 						maxbytes, i_size_read(inode));
-	case SEEK_DATA:
-		return ext4_seek_data(file, offset, maxbytes);
 	case SEEK_HOLE:
-		return ext4_seek_hole(file, offset, maxbytes);
+		inode_lock_shared(inode);
+		offset = iomap_seek_hole(inode, offset, &ext4_iomap_ops);
+		inode_unlock_shared(inode);
+		break;
+	case SEEK_DATA:
+		inode_lock_shared(inode);
+		offset = iomap_seek_data(inode, offset, &ext4_iomap_ops);
+		inode_unlock_shared(inode);
+		break;
 	}
 
-	return -EINVAL;
+	if (offset < 0)
+		return offset;
+	return vfs_setpos(file, offset, maxbytes);
 }
 
 const struct file_operations ext4_file_operations = {
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ab6ab835255e..f5895ea6ac70 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3400,7 +3400,6 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
 		return try_to_free_buffers(page);
 }
 
-#ifdef CONFIG_FS_DAX
 static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			    unsigned flags, struct iomap *iomap)
 {
@@ -3409,6 +3408,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	unsigned long first_block = offset >> blkbits;
 	unsigned long last_block = (offset + length - 1) >> blkbits;
 	struct ext4_map_blocks map;
+	bool delalloc = false;
 	int ret;
 
 	if ((flags & IOMAP_REPORT) && ext4_has_inline_data(inode)) {
@@ -3425,6 +3425,29 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 
 	if (!(flags & IOMAP_WRITE)) {
 		ret = ext4_map_blocks(NULL, inode, &map, 0);
+		if (ret < 0)
+			return ret;
+		if (!ret) {
+			struct extent_status es = {};
+
+			ext4_es_find_delayed_extent_range(inode, map.m_lblk,
+					map.m_lblk + map.m_len - 1, &es);
+			/* Is delalloc data before next block in extent tree? */
+			if (es.es_len && es.es_lblk < map.m_lblk + map.m_len) {
+				ext4_lblk_t offs = 0;
+
+				if (es.es_lblk < map.m_lblk)
+					offs = map.m_lblk - es.es_lblk;
+				map.m_lblk = es.es_lblk + offs;
+				map.m_pblk = ext4_es_pblock(&es) + offs;
+				map.m_len = es.es_len - offs;
+				if (ext4_es_is_unwritten(&es))
+					map.m_flags |= EXT4_MAP_UNWRITTEN;
+				if (ext4_es_is_delayed(&es))
+					delalloc = true;
+				ret = 1;
+			}
+		}
 	} else {
 		int dio_credits;
 		handle_t *handle;
@@ -3486,11 +3509,14 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	else
 		iomap->dax_dev = NULL;
 	iomap->offset = first_block << blkbits;
+	iomap->length = (u64)map.m_len << blkbits;
 
 	if (ret == 0) {
 		iomap->type = IOMAP_HOLE;
 		iomap->addr = IOMAP_NULL_ADDR;
-		iomap->length = (u64)map.m_len << blkbits;
+	} else if (delalloc) {
+		iomap->type = IOMAP_DELALLOC;
+		iomap->addr = IOMAP_NULL_ADDR;
 	} else {
 		if (map.m_flags & EXT4_MAP_MAPPED) {
 			iomap->type = IOMAP_MAPPED;
@@ -3501,7 +3527,6 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			return -EIO;
 		}
 		iomap->addr = (u64)map.m_pblk << blkbits;
-		iomap->length = (u64)map.m_len << blkbits;
 	}
 
 	if (map.m_flags & EXT4_MAP_NEW)
@@ -3567,8 +3592,6 @@ const struct iomap_ops ext4_iomap_ops = {
 	.iomap_end		= ext4_iomap_end,
 };
 
-#endif
-
 static int ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
 			    ssize_t size, void *private)
 {
@@ -6132,70 +6155,3 @@ int ext4_filemap_fault(struct vm_fault *vmf)
 
 	return err;
 }
-
-/*
- * Find the first extent at or after @lblk in an inode that is not a hole.
- * Search for @map_len blocks at most. The extent is returned in @result.
- *
- * The function returns 1 if we found an extent. The function returns 0 in
- * case there is no extent at or after @lblk and in that case also sets
- * @result->es_len to 0. In case of error, the error code is returned.
- */
-int ext4_get_next_extent(struct inode *inode, ext4_lblk_t lblk,
-			 unsigned int map_len, struct extent_status *result)
-{
-	struct ext4_map_blocks map;
-	struct extent_status es = {};
-	int ret;
-
-	map.m_lblk = lblk;
-	map.m_len = map_len;
-
-	/*
-	 * For non-extent based files this loop may iterate several times since
-	 * we do not determine full hole size.
-	 */
-	while (map.m_len > 0) {
-		ret = ext4_map_blocks(NULL, inode, &map, 0);
-		if (ret < 0)
-			return ret;
-		/* There's extent covering m_lblk? Just return it. */
-		if (ret > 0) {
-			int status;
-
-			ext4_es_store_pblock(result, map.m_pblk);
-			result->es_lblk = map.m_lblk;
-			result->es_len = map.m_len;
-			if (map.m_flags & EXT4_MAP_UNWRITTEN)
-				status = EXTENT_STATUS_UNWRITTEN;
-			else
-				status = EXTENT_STATUS_WRITTEN;
-			ext4_es_store_status(result, status);
-			return 1;
-		}
-		ext4_es_find_delayed_extent_range(inode, map.m_lblk,
-						  map.m_lblk + map.m_len - 1,
-						  &es);
-		/* Is delalloc data before next block in extent tree? */
-		if (es.es_len && es.es_lblk < map.m_lblk + map.m_len) {
-			ext4_lblk_t offset = 0;
-
-			if (es.es_lblk < lblk)
-				offset = lblk - es.es_lblk;
-			result->es_lblk = es.es_lblk + offset;
-			ext4_es_store_pblock(result,
-					     ext4_es_pblock(&es) + offset);
-			result->es_len = es.es_len - offset;
-			ext4_es_store_status(result, ext4_es_status(&es));
-
-			return 1;
-		}
-		/* There's a hole at m_lblk, advance us after it */
-		map.m_lblk += map.m_len;
-		map_len -= map.m_len;
-		map.m_len = map_len;
-		cond_resched();
-	}
-	result->es_len = 0;
-	return 0;
-}
-- 
2.13.3