[Devel] [PATCH RHEL7 COMMIT] ms/ext4: return hole from ext4_map_blocks()

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.16.1.vz7.32.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.16.1.vz7.30.8
------>
commit 924e0c832821a548458cd389c6cefb687a686e32
Author: Jan Kara <jack at suse.cz>
Date:   Fri Apr 28 16:16:15 2017 +0400

    ms/ext4: return hole from ext4_map_blocks()
    
    commit facab4d9711e7aa3532cb82643803e8f1b9518e8 upstream.
    
    Currently, ext4_map_blocks() just returns 0 when it finds a hole and
    allocation is not requested. However we have all the information
    available to tell how large the hole actually is and there are callers
    of ext4_map_blocks() which would save some block-by-block hole iteration
    if they knew this information. So fill in struct ext4_map_blocks even
    for holes with the information we have. We keep returning 0 for holes to
    maintain backward compatibility of the function.
    
    Signed-off-by: Jan Kara <jack at suse.cz>
    Signed-off-by: Theodore Ts'o <tytso at mit.edu>
    
    https://jira.sw.ru/browse/PSBM-65551
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 fs/ext4/extents.c  | 11 +++++++++--
 fs/ext4/indirect.c | 19 +++++++++++++++++--
 fs/ext4/inode.c    | 15 ++++++++++-----
 3 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 04148a4..0f7c73f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4390,13 +4390,20 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
 		ext4_lblk_t hole_start, hole_len;
 
+		hole_start = map->m_lblk;
+		hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
 		/*
 		 * put just found gap into cache to speed up
 		 * subsequent requests
 		 */
-		hole_start = map->m_lblk;
-		hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
 		ext4_ext_put_gap_in_cache(inode, hole_start, hole_len);
+
+		/* Update hole_len to reflect hole size after map->m_lblk */
+		if (hole_start != map->m_lblk)
+			hole_len -= map->m_lblk - hole_start;
+		map->m_pblk = 0;
+		map->m_len = min_t(unsigned int, map->m_len, hole_len);
+
 		goto out2;
 	}
 
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 0d8967a..c0915c5 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -566,8 +566,23 @@ int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
 		goto got_it;
 	}
 
-	/* Next simple case - plain lookup or failed read of indirect block */
-	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0 || err == -EIO)
+	/* Next simple case - plain lookup failed */
+	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
+		unsigned epb = inode->i_sb->s_blocksize / sizeof(u32);
+		int i;
+
+		/* Count number blocks in a subtree under 'partial' */
+		count = 1;
+		for (i = 0; partial + i != chain + depth - 1; i++)
+			count *= epb;
+		/* Fill in size of a hole we found */
+		map->m_pblk = 0;
+		map->m_len = min_t(unsigned int, map->m_len, count);
+		goto cleanup;
+	}
+
+	/* Failed read of indirect block */
+	if (err == -EIO)
 		goto cleanup;
 
 	/*
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 33eee14..83b58ae 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -461,13 +461,13 @@ static void ext4_map_blocks_es_recheck(handle_t *handle,
  * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
  * based files
  *
- * On success, it returns the number of blocks being mapped or allocated.
- * if create==0 and the blocks are pre-allocated and unwritten block,
- * the result buffer head is unmapped. If the create ==1, it will make sure
- * the buffer head is mapped.
+ * On success, it returns the number of blocks being mapped or allocated.  if
+ * create==0 and the blocks are pre-allocated and unwritten, the resulting @map
+ * is marked as unwritten. If the create == 1, it will mark @map as mapped.
  *
  * It returns 0 if plain look up failed (blocks have not been allocated), in
- * that case, buffer head is unmapped
+ * that case, @map is returned as unmapped but we still do fill map->m_len to
+ * indicate the length of a hole starting at map->m_lblk.
  *
  * It returns the error in case of allocation failure.
  */
@@ -511,6 +511,11 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
 				retval = map->m_len;
 			map->m_len = retval;
 		} else if (ext4_es_is_delayed(&es) || ext4_es_is_hole(&es)) {
+			map->m_pblk = 0;
+			retval = es.es_len - (map->m_lblk - es.es_lblk);
+			if (retval > map->m_len)
+				retval = map->m_len;
+			map->m_len = retval;
 			retval = 0;
 		} else {
 			BUG_ON(1);