iomap: better document the IOMAP_F_* flags

The documentation for IOMAP_F_* is a bit disorganized, and doesn't
mention the fact that most flags are set by the file system and consumed
by the iomap core, while IOMAP_F_SIZE_CHANGED is set by the core and
consumed by the file system.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 0f741eebf3a76b294a33c9c93513829f8f59cc30..8016700e61214d5dab6da040e36ab303c8dbf0de 100644 (file)
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -30,23 +30,38 @@ struct vm_fault;
 #define IOMAP_INLINE   0x05    /* data inline in the inode */
 
 /*
- * Flags for all iomap mappings:
+ * Flags reported by the file system from iomap_begin:
+ *
+ * IOMAP_F_NEW indicates that the blocks have been newly allocated and need
+ * zeroing for areas that no data is copied to.
  *
  * IOMAP_F_DIRTY indicates the inode has uncommitted metadata needed to access
  * written data and requires fdatasync to commit them to persistent storage.
  * This needs to take into account metadata changes that *may* be made at IO
  * completion, such as file size updates from direct IO.
+ *
+ * IOMAP_F_SHARED indicates that the blocks are shared, and will need to be
+ * unshared as part a write.
+ *
+ * IOMAP_F_MERGED indicates that the iomap contains the merge of multiple block
+ * mappings.
+ *
+ * IOMAP_F_BUFFER_HEAD indicates that the file system requires the use of
+ * buffer heads for this mapping.
  */
-#define IOMAP_F_NEW            0x01    /* blocks have been newly allocated */
-#define IOMAP_F_DIRTY          0x02    /* uncommitted metadata */
-#define IOMAP_F_BUFFER_HEAD    0x04    /* file system requires buffer heads */
-#define IOMAP_F_SIZE_CHANGED   0x08    /* file size has changed */
+#define IOMAP_F_NEW            0x01
+#define IOMAP_F_DIRTY          0x02
+#define IOMAP_F_SHARED         0x04
+#define IOMAP_F_MERGED         0x08
+#define IOMAP_F_BUFFER_HEAD    0x10
 
 /*
- * Flags that only need to be reported for IOMAP_REPORT requests:
+ * Flags set by the core iomap code during operations:
+ *
+ * IOMAP_F_SIZE_CHANGED indicates to the iomap_end method that the file size
+ * has changed as the result of this write operation.
  */
-#define IOMAP_F_MERGED         0x10    /* contains multiple blocks/extents */
-#define IOMAP_F_SHARED         0x20    /* block shared with another file */
+#define IOMAP_F_SIZE_CHANGED   0x100
 
 /*
  * Flags from 0x1000 up are for file system specific usage: