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, 18 insertions, 5 deletions

diff --git a/fs/exofs/ios.c b/fs/exofs/ios.c
index 4f679317ca54..2b81f99fd62c 100644
--- a/fs/exofs/ios.c
+++ b/fs/exofs/ios.c
@@ -107,6 +107,19 @@ void exofs_put_io_state(struct exofs_io_state *ios)
 	}
 }
 
+unsigned exofs_layout_od_id(struct exofs_layout *layout,
+			    osd_id obj_no, unsigned layout_index)
+{
+	return layout_index;
+}
+
+static inline struct osd_dev *exofs_ios_od(struct exofs_io_state *ios,
+					   unsigned layout_index)
+{
+	return ios->layout->s_ods[
+		exofs_layout_od_id(ios->layout, ios->obj.id, layout_index)];
+}
+
 static void _sync_done(struct exofs_io_state *ios, void *p)
 {
 	struct completion *waiting = p;
@@ -242,7 +255,7 @@ int exofs_sbi_create(struct exofs_io_state *ios)
 	for (i = 0; i < ios->layout->s_numdevs; i++) {
 		struct osd_request *or;
 
-		or = osd_start_request(ios->layout->s_ods[i], GFP_KERNEL);
+		or = osd_start_request(exofs_ios_od(ios, i), GFP_KERNEL);
 		if (unlikely(!or)) {
 			EXOFS_ERR("%s: osd_start_request failed\n", __func__);
 			ret = -ENOMEM;
@@ -266,7 +279,7 @@ int exofs_sbi_remove(struct exofs_io_state *ios)
 	for (i = 0; i < ios->layout->s_numdevs; i++) {
 		struct osd_request *or;
 
-		or = osd_start_request(ios->layout->s_ods[i], GFP_KERNEL);
+		or = osd_start_request(exofs_ios_od(ios, i), GFP_KERNEL);
 		if (unlikely(!or)) {
 			EXOFS_ERR("%s: osd_start_request failed\n", __func__);
 			ret = -ENOMEM;
@@ -290,7 +303,7 @@ int exofs_sbi_write(struct exofs_io_state *ios)
 	for (i = 0; i < ios->layout->s_numdevs; i++) {
 		struct osd_request *or;
 
-		or = osd_start_request(ios->layout->s_ods[i], GFP_KERNEL);
+		or = osd_start_request(exofs_ios_od(ios, i), GFP_KERNEL);
 		if (unlikely(!or)) {
 			EXOFS_ERR("%s: osd_start_request failed\n", __func__);
 			ret = -ENOMEM;
@@ -361,7 +374,7 @@ int exofs_sbi_read(struct exofs_io_state *ios)
 	unsigned first_dev = (unsigned)ios->obj.id;
 
 	first_dev %= ios->layout->s_numdevs;
-	or = osd_start_request(ios->layout->s_ods[first_dev], GFP_KERNEL);
+	or = osd_start_request(exofs_ios_od(ios, first_dev), GFP_KERNEL);
 	if (unlikely(!or)) {
 		EXOFS_ERR("%s: osd_start_request failed\n", __func__);
 		return -ENOMEM;
@@ -442,7 +455,7 @@ int exofs_oi_truncate(struct exofs_i_info *oi, u64 size)
 	for (i = 0; i < sbi->layout.s_numdevs; i++) {
 		struct osd_request *or;
 
-		or = osd_start_request(sbi->layout.s_ods[i], GFP_KERNEL);
+		or = osd_start_request(exofs_ios_od(ios, i), GFP_KERNEL);
 		if (unlikely(!or)) {
 			EXOFS_ERR("%s: osd_start_request failed\n", __func__);
 			ret = -ENOMEM;