[PATCH v3 4/4] NFSD: handle unaligned DIO for NFS reexport

[Mike Snitzer <snitzer@kernel.org>]

NFS doesn't have any DIO alignment constraints but it doesn't support
STATX_DIOALIGN, so update NFSD such that it doesn't disable the use of
NFSD_IO_DIRECT if it is reexporting NFS.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 fs/nfs/export.c          |  3 ++-
 fs/nfsd/filecache.c      | 11 +++++++++++
 include/linux/exportfs.h | 13 +++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/export.c b/fs/nfs/export.c
index e9c233b6fd209..2cae75ba6b35d 100644
--- a/fs/nfs/export.c
+++ b/fs/nfs/export.c
@@ -155,5 +155,6 @@ const struct export_operations nfs_export_ops = {
 		 EXPORT_OP_REMOTE_FS		|
 		 EXPORT_OP_NOATOMIC_ATTR	|
 		 EXPORT_OP_FLUSH_ON_CLOSE	|
-		 EXPORT_OP_NOLOCKS,
+		 EXPORT_OP_NOLOCKS		|
+		 EXPORT_OP_NO_DIOALIGN_NEEDED,
 };
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 5601e839a72da..ea489dd44fd9a 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -1066,6 +1066,17 @@ nfsd_file_getattr(const struct svc_fh *fhp, struct nfsd_file *nf)
 	     nfsd_io_cache_write != NFSD_IO_DIRECT))
 		return nfs_ok;
 
+	if (exportfs_handles_unaligned_dio(nf->nf_file->f_path.mnt->mnt_sb->s_export_op)) {
+		/* Underlying filesystem doesn't support STATX_DIOALIGN
+		 * but it can handle all unaligned DIO, so establish
+		 * DIO alignment that is accommodating.
+		 */
+		nf->nf_dio_mem_align = 4;
+		nf->nf_dio_offset_align = PAGE_SIZE;
+		nf->nf_dio_read_offset_align = nf->nf_dio_offset_align;
+		return nfs_ok;
+	}
+
 	status = fh_getattr(fhp, &stat);
 	if (status != nfs_ok)
 		return status;
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 9369a607224c1..626b8486dd985 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -247,6 +247,7 @@ struct export_operations {
 						*/
 #define EXPORT_OP_FLUSH_ON_CLOSE	(0x20) /* fs flushes file data on close */
 #define EXPORT_OP_NOLOCKS		(0x40) /* no file locking support */
+#define EXPORT_OP_NO_DIOALIGN_NEEDED	(0x80) /* fs can handle unaligned DIO */
 	unsigned long	flags;
 };
 
@@ -262,6 +263,18 @@ exportfs_cannot_lock(const struct export_operations *export_ops)
 	return export_ops->flags & EXPORT_OP_NOLOCKS;
 }
 
+/**
+ * exportfs_handles_unaligned_dio() - check if export can handle unaligned DIO
+ * @export_ops:	the nfs export operations to check
+ *
+ * Returns true if the export can handle unaligned DIO.
+ */
+static inline bool
+exportfs_handles_unaligned_dio(const struct export_operations *export_ops)
+{
+	return export_ops->flags & EXPORT_OP_NO_DIOALIGN_NEEDED;
+}
+
 extern int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
 				    int *max_len, struct inode *parent,
 				    int flags);
-- 
2.44.0