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>

1 files changed, 25 insertions, 5 deletions

diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index 092ab499f2b691..568ecf0a880f11 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -70,8 +70,15 @@ EXPORT_SYMBOL_GPL(nfs_pageio_init_read);
 
 void nfs_pageio_reset_read_mds(struct nfs_pageio_descriptor *pgio)
 {
+	struct nfs_pgio_mirror *mirror;
+
 	pgio->pg_ops = &nfs_pgio_rw_ops;
-	pgio->pg_bsize = NFS_SERVER(pgio->pg_inode)->rsize;
+
+	/* read path should never have more than one mirror */
+	WARN_ON_ONCE(pgio->pg_mirror_count != 1);
+
+	mirror = &pgio->pg_mirrors[0];
+	mirror->pg_bsize = NFS_SERVER(pgio->pg_inode)->rsize;
 }
 EXPORT_SYMBOL_GPL(nfs_pageio_reset_read_mds);
 
@@ -81,6 +88,7 @@ int nfs_readpage_async(struct nfs_open_context *ctx, struct inode *inode,
 	struct nfs_page	*new;
 	unsigned int len;
 	struct nfs_pageio_descriptor pgio;
+	struct nfs_pgio_mirror *pgm;
 
 	len = nfs_page_length(page);
 	if (len == 0)
@@ -97,7 +105,13 @@ int nfs_readpage_async(struct nfs_open_context *ctx, struct inode *inode,
 			     &nfs_async_read_completion_ops);
 	nfs_pageio_add_request(&pgio, new);
 	nfs_pageio_complete(&pgio);
-	NFS_I(inode)->read_io += pgio.pg_bytes_written;
+
+	/* It doesn't make sense to do mirrored reads! */
+	WARN_ON_ONCE(pgio.pg_mirror_count != 1);
+
+	pgm = &pgio.pg_mirrors[0];
+	NFS_I(inode)->read_io += pgm->pg_bytes_written;
+
 	return 0;
 }
 
@@ -352,6 +366,7 @@ int nfs_readpages(struct file *filp, struct address_space *mapping,
 		struct list_head *pages, unsigned nr_pages)
 {
 	struct nfs_pageio_descriptor pgio;
+	struct nfs_pgio_mirror *pgm;
 	struct nfs_readdesc desc = {
 		.pgio = &pgio,
 	};
@@ -387,10 +402,15 @@ int nfs_readpages(struct file *filp, struct address_space *mapping,
 			     &nfs_async_read_completion_ops);
 
 	ret = read_cache_pages(mapping, pages, readpage_async_filler, &desc);
-
 	nfs_pageio_complete(&pgio);
-	NFS_I(inode)->read_io += pgio.pg_bytes_written;
-	npages = (pgio.pg_bytes_written + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+
+	/* It doesn't make sense to do mirrored reads! */
+	WARN_ON_ONCE(pgio.pg_mirror_count != 1);
+
+	pgm = &pgio.pg_mirrors[0];
+	NFS_I(inode)->read_io += pgm->pg_bytes_written;
+	npages = (pgm->pg_bytes_written + PAGE_CACHE_SIZE - 1) >>
+		 PAGE_CACHE_SHIFT;
 	nfs_add_stats(inode, NFSIOS_READPAGES, npages);
 read_complete:
 	put_nfs_open_context(desc.ctx);