ext4: improve ext_debug() msg in case of block allocation failure

ext4_map_blocks() has ext_debug msg early at the start of function.
We also get ext_debug msg if we could allocate a block from
ext4_ext_map_blocks(). But there is no ext_debug() msg in case of
block allocation failure. So add one along with error code.

Also add more info in ext_debug() msg like how many blocks were allocated
v/s how many were requested in ext4_ext_map_blocks().
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/1610ec2aa932396be00f9d552fe29da473ead176.1589086800.git.riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -4246,10 +4246,10 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	newblock = ext4_mb_new_blocks(handle, &ar, &err);
 	if (!newblock)
 		goto out2;
-	ext_debug("allocate new block: goal %llu, found %llu/%u\n",
-		  ar.goal, newblock, allocated);
 	allocated_clusters = ar.len;
 	ar.len = EXT4_C2B(sbi, ar.len) - offset;
+	ext_debug("allocate new block: goal %llu, found %llu/%u, requested %u\n",
+		  ar.goal, newblock, ar.len, allocated);
 	if (ar.len > allocated)
 		ar.len = allocated;
 

fs/ext4/inode.c

@@ -732,6 +732,10 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
 				return ret;
 		}
 	}
+
+	if (retval < 0)
+		ext_debug("failed for inode %lu with err %d\n",
+			  inode->i_ino, retval);
 	return retval;
 }