NFSD: Add io_cache_{read,write} controls to debugfs

Add 'io_cache_read' to NFSD's debugfs interface so that any data
read by NFSD will either be:
- cached using page cache (NFSD_IO_BUFFERED=0)
- cached but removed from the page cache upon completion
  (NFSD_IO_DONTCACHE=1).

io_cache_read may be set by writing to:
  /sys/kernel/debug/nfsd/io_cache_read

Add 'io_cache_write' to NFSD's debugfs interface so that any data
written by NFSD will either be:
- cached using page cache (NFSD_IO_BUFFERED=0)
- cached but removed from the page cache upon completion
  (NFSD_IO_DONTCACHE=1).

io_cache_write may be set by writing to:
  /sys/kernel/debug/nfsd/io_cache_write

The default value for both settings is NFSD_IO_BUFFERED, which is
NFSD's existing behavior for both read and write. Changes to these
settings take immediate effect for all exports and NFS versions.

Currently only xfs and ext4 implement RWF_DONTCACHE. For file
systems that do not implement RWF_DONTCACHE, NFSD use only buffered
I/O when the io_cache setting is NFSD_IO_DONTCACHE.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 3cd3b9e069f4..714777c221ed 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -49,6 +49,8 @@
 #define NFSDDBG_FACILITY		NFSDDBG_FILEOP
 
 bool nfsd_disable_splice_read __read_mostly;
+u64 nfsd_io_cache_read __read_mostly = NFSD_IO_BUFFERED;
+u64 nfsd_io_cache_write __read_mostly = NFSD_IO_BUFFERED;
 
 /**
  * nfserrno - Map Linux errnos to NFS errnos
@@ -1099,6 +1101,16 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	size_t len;
 
 	init_sync_kiocb(&kiocb, file);
+
+	switch (nfsd_io_cache_read) {
+	case NFSD_IO_BUFFERED:
+		break;
+	case NFSD_IO_DONTCACHE:
+		if (file->f_op->fop_flags & FOP_DONTCACHE)
+			kiocb.ki_flags = IOCB_DONTCACHE;
+		break;
+	}
+
 	kiocb.ki_pos = offset;
 
 	v = 0;
@@ -1224,6 +1236,15 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	since = READ_ONCE(file->f_wb_err);
 	if (verf)
 		nfsd_copy_write_verifier(verf, nn);
+
+	switch (nfsd_io_cache_write) {
+	case NFSD_IO_BUFFERED:
+		break;
+	case NFSD_IO_DONTCACHE:
+		if (file->f_op->fop_flags & FOP_DONTCACHE)
+			kiocb.ki_flags |= IOCB_DONTCACHE;
+		break;
+	}
 	host_err = vfs_iocb_iter_write(file, &kiocb, &iter);
 	if (host_err < 0) {
 		commit_reset_write_verifier(nn, rqstp, host_err);