nfs: add mirroring support to pgio layer

This patch adds mirrored write support to the pgio layer. The default
is to use one mirror, but pgio callers may define callbacks to change
this to any value up to the (arbitrarily selected) limit of 16.

The basic idea is to break out members of nfs_pageio_descriptor that cannot
be shared between mirrored DSes and put them in a new structure.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>

2 files changed, 18 insertions, 3 deletions

diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index 479c566c4ddc..3eb072dbce83 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -58,6 +58,8 @@ struct nfs_pageio_ops {
         size_t  (*pg_test)(struct nfs_pageio_descriptor *, struct nfs_page *,
                            struct nfs_page *);
         int     (*pg_doio)(struct nfs_pageio_descriptor *);
+        unsigned int    (*pg_get_mirror_count)(struct nfs_pageio_descriptor *,
+                                       struct nfs_page *);
         void    (*pg_cleanup)(struct nfs_pageio_descriptor *);
 };
 
@@ -74,15 +76,17 @@ struct nfs_rw_ops {
                             struct rpc_task_setup *, int);
 };
 
-struct nfs_pageio_descriptor {
+struct nfs_pgio_mirror {
         struct list_head        pg_list;
         unsigned long           pg_bytes_written;
         size_t                  pg_count;
         size_t                  pg_bsize;
         unsigned int            pg_base;
-        unsigned char           pg_moreio : 1,
-                                pg_recoalesce : 1;
+        unsigned char           pg_recoalesce : 1;
+};
 
+struct nfs_pageio_descriptor {
+        unsigned char           pg_moreio : 1;
         struct inode            *pg_inode;
         const struct nfs_pageio_ops *pg_ops;
         const struct nfs_rw_ops *pg_rw_ops;
@@ -93,8 +97,18 @@ struct nfs_pageio_descriptor {
         struct pnfs_layout_segment *pg_lseg;
         struct nfs_direct_req   *pg_dreq;
         void                    *pg_layout_private;
+        unsigned int            pg_bsize;       /* default bsize for mirrors */
+
+        u32                     pg_mirror_count;
+        struct nfs_pgio_mirror  *pg_mirrors;
+        struct nfs_pgio_mirror  pg_mirrors_static[1];
+        struct nfs_pgio_mirror  *pg_mirrors_dynamic;
+        u32                     pg_mirror_idx;  /* current mirror */
 };
 
+/* arbitrarily selected limit to number of mirrors */
+#define NFS_PAGEIO_DESCRIPTOR_MIRROR_MAX 16
+
 #define NFS_WBACK_BUSY(req)     (test_bit(PG_BUSY,&(req)->wb_flags))
 
 extern  struct nfs_page *nfs_create_request(struct nfs_open_context *ctx,
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 5bc99f04a550..6400a1e01aa4 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1329,6 +1329,7 @@ struct nfs_pgio_header {
         struct nfs_page_array   page_array;
         struct nfs_client       *ds_clp;        /* pNFS data server */
         int                     ds_commit_idx;  /* ds index if ds_clp is set */
+        int                     pgio_mirror_idx;/* mirror index in pgio layer */
 };
 
 struct nfs_mds_commit_info {