exofs: Define on-disk per-inode optional layout attribute

* Layouts describe the way a file is spread on multiple devices.
  The layout information is stored in the objects attribute introduced
  in this patch.

* There can be multiple generating function for the layout.
  Currently defined:
    - No attribute present - use below moving-window on global
      device table, all devices.
      (This is the only one currently used in exofs)
    - an obj_id generated moving window - the obj_id is a randomizing
      factor in the otherwise global map layout.
    - An explicit layout stored, including a data_map and a device
      index list.
    - More might be defined in future ...

* There are two attributes defined of the same structure:
  A-data-files-layout - This layout is used by data-files. If present
                        at a directory, all files of that directory will
                        be created with this layout.
  A-meta-data-layout - This layout is used by a directory and other
                       meta-data information. Also inherited at creation
                       of subdirectories.

* At creation time inodes are created with the layout specified above.
  A usermode utility may change the creation layout on a give directory
  or file. Which in the case of directories, will also apply to newly
  created files/subdirectories, children of that directory.
  In the simple unaltered case of a newly created exofs, no layout
  attributes are present, and all layouts adhere to the layout specified
  at the device-table.

* In case of a future file system loaded in an old exofs-driver.
  At iget(), the generating_function is inspected and if not supported
  will return an IO error to the application and the inode will not
  be loaded. So not to damage any data.
  Note: After this patch we do not yet support any type of layout
        only the RAID0 patch that enables striping at the super-block
        level will add support for RAID0 layouts above. This way we
        are past and future compatible and fully bisectable.

* Access to the device table is done by an accessor since
  it will change according to above information.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/fs/exofs/common.h b/fs/exofs/common.h
index b1b178e..f0d5203 100644
--- a/fs/exofs/common.h
+++ b/fs/exofs/common.h
@@ -55,6 +55,8 @@
 /* exofs Application specific page/attribute */
 # define EXOFS_APAGE_FS_DATA	(OSD_APAGE_APP_DEFINED_FIRST + 3)
 # define EXOFS_ATTR_INODE_DATA	1
+# define EXOFS_ATTR_INODE_FILE_LAYOUT	2
+# define EXOFS_ATTR_INODE_DIR_LAYOUT	3
 
 /*
  * The maximum number of files we can have is limited by the size of the
@@ -206,4 +208,41 @@ enum {
 	(((name_len) + offsetof(struct exofs_dir_entry, name)  + \
 	  EXOFS_DIR_ROUND) & ~EXOFS_DIR_ROUND)
 
+/*
+ * The on-disk (optional) layout structure.
+ * sits in an EXOFS_ATTR_INODE_FILE_LAYOUT or EXOFS_ATTR_INODE_DIR_LAYOUT
+ * attribute, attached to any inode, usually to a directory.
+ */
+
+enum exofs_inode_layout_gen_functions {
+	LAYOUT_MOVING_WINDOW = 0,
+	LAYOUT_IMPLICT = 1,
+};
+
+struct exofs_on_disk_inode_layout {
+	__le16 gen_func; /* One of enum exofs_inode_layout_gen_functions */
+	__le16 pad;
+	union {
+		/* gen_func == LAYOUT_MOVING_WINDOW (default) */
+		struct exofs_layout_sliding_window {
+			__le32 num_devices; /* first n devices in global-table*/
+		} sliding_window __packed;
+
+		/* gen_func == LAYOUT_IMPLICT */
+		struct exofs_layout_implict_list {
+			struct exofs_dt_data_map data_map;
+			/* Variable array of size data_map.cb_num_comps. These
+			 * are device indexes of the devices in the global table
+			 */
+			__le32 dev_indexes[];
+		} implict __packed;
+	};
+} __packed;
+
+static inline size_t exofs_on_disk_inode_layout_size(unsigned max_devs)
+{
+	return sizeof(struct exofs_on_disk_inode_layout) +
+		max_devs * sizeof(__le32);
+}
+
 #endif /*ifndef __EXOFS_COM_H__*/