[PATCH v2 2/6] NFSD: Apply per-export I/O modes to READ and WRITE

[Jeff Layton <jlayton@kernel.org>]

Resolve each export's effective I/O mode (explicit setting, else the
global io_cache_read/write knob) in nfsd_iter_read and nfsd_vfs_write,
and skip splice for reads on exports whose effective read mode is not
buffered. Update the debugfs knob comments to match.

That per-export check makes the coupling between the debugfs knobs
unnecessary, and it defeats per-export settings, so drop it:

- io_cache_read=dontcache/direct no longer sets disable-splice-read,
  which kept read_io=buffered exports from ever using splice.
- disable-splice-read=0 no longer resets io_cache_read to buffered.

disable-splice-read is now only a global "never splice" override.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/debugfs.c | 23 ++++++++---------------
 fs/nfsd/nfs4xdr.c |  6 ++++--
 fs/nfsd/vfs.c     | 39 ++++++++++++++++++++++++++++++++++++---
 fs/nfsd/vfs.h     |  2 ++
 4 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
index 4af1e6b8b212..d48297e45d7d 100644
--- a/fs/nfsd/debugfs.c
+++ b/fs/nfsd/debugfs.c
@@ -16,6 +16,10 @@ static struct dentry *nfsd_top_dir __read_mostly;
  * The default value of this setting is zero (page splicing is
  * allowed). This setting takes immediate effect for all NFS
  * versions, all exports, and in all NFSD net namespaces.
+ *
+ * Splice is used only on exports whose effective read I/O mode is
+ * buffered, so this setting is independent of io_cache_read and
+ * read_io=.
  */
 
 static int nfsd_dsr_get(void *data, u64 *val)
@@ -27,12 +31,6 @@ static int nfsd_dsr_get(void *data, u64 *val)
 static int nfsd_dsr_set(void *data, u64 val)
 {
 	nfsd_disable_splice_read = (val > 0);
-	if (!nfsd_disable_splice_read) {
-		/*
-		 * Must use buffered I/O if splice_read is enabled.
-		 */
-		nfsd_io_cache_read = NFSD_IO_BUFFERED;
-	}
 	return 0;
 }
 
@@ -47,7 +45,8 @@ DEFINE_DEBUGFS_ATTRIBUTE(nfsd_dsr_fops, nfsd_dsr_get, nfsd_dsr_set, "%llu\n");
  *   %2: NFS READ will use direct IO
  *
  * This setting takes immediate effect for all NFS versions,
- * all exports, and in all NFSD net namespaces.
+ * all exports without an explicit read_io= setting, and in all
+ * NFSD net namespaces.
  */
 
 static int nfsd_io_cache_read_get(void *data, u64 *val)
@@ -62,15 +61,8 @@ static int nfsd_io_cache_read_set(void *data, u64 val)
 
 	switch (val) {
 	case NFSD_IO_BUFFERED:
-		nfsd_io_cache_read = NFSD_IO_BUFFERED;
-		break;
 	case NFSD_IO_DONTCACHE:
 	case NFSD_IO_DIRECT:
-		/*
-		 * Must disable splice_read when enabling
-		 * NFSD_IO_DONTCACHE.
-		 */
-		nfsd_disable_splice_read = true;
 		nfsd_io_cache_read = val;
 		break;
 	default:
@@ -92,7 +84,8 @@ DEFINE_DEBUGFS_ATTRIBUTE(nfsd_io_cache_read_fops, nfsd_io_cache_read_get,
  *   %1: NFS WRITE will use dontcache (buffered IO w/ dropbehind)
  *
  * This setting takes immediate effect for all NFS versions,
- * all exports, and in all NFSD net namespaces.
+ * all exports without an explicit write_io= setting, and in all
+ * NFSD net namespaces.
  */
 
 static int nfsd_io_cache_write_get(void *data, u64 *val)
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 4d983444604a..d4a88bef8444 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -5366,7 +5366,8 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	maxcount = min_t(unsigned long, read->rd_length,
 			 (xdr->buf->buflen - xdr->buf->len));
 
-	if (file->f_op->splice_read && splice_ok)
+	if (file->f_op->splice_read && splice_ok &&
+	    nfsd_read_io_mode(read->rd_fhp->fh_export) == NFSD_IO_BUFFERED)
 		nfserr = nfsd4_encode_splice_read(resp, read, file, maxcount);
 	else
 		nfserr = nfsd4_encode_readv(resp, read, maxcount);
@@ -6264,7 +6265,8 @@ nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
 	maxcount = min_t(unsigned long, read->rd_length,
 			 (xdr->buf->buflen - xdr->buf->len));
 
-	if (file->f_op->splice_read && splice_ok)
+	if (file->f_op->splice_read && splice_ok &&
+	    nfsd_read_io_mode(read->rd_fhp->fh_export) == NFSD_IO_BUFFERED)
 		nfserr = nfsd4_encode_splice_read(resp, read, file, maxcount);
 	else
 		nfserr = nfsd4_encode_readv(resp, read, maxcount);
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index f59a55f89c88..779ad3a61172 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1266,6 +1266,38 @@ static bool nfsd_direct_read_ok(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	return true;
 }
 
+/**
+ * nfsd_read_io_mode - effective NFS READ I/O mode for an export
+ * @exp: export being accessed
+ *
+ * An export without an explicit read_io= setting follows the global
+ * nfsd_io_cache_read knob.
+ *
+ * Returns one of NFSD_IO_BUFFERED, NFSD_IO_DONTCACHE, or NFSD_IO_DIRECT.
+ */
+int nfsd_read_io_mode(struct svc_export *exp)
+{
+	if (exp->ex_read_io == NFSD_IO_DEFAULT)
+		return nfsd_io_cache_read;
+	return exp->ex_read_io;
+}
+
+/**
+ * nfsd_write_io_mode - effective NFS WRITE I/O mode for an export
+ * @exp: export being accessed
+ *
+ * An export without an explicit write_io= setting follows the global
+ * nfsd_io_cache_write knob.
+ *
+ * Returns one of NFSD_IO_BUFFERED, NFSD_IO_DONTCACHE, or NFSD_IO_DIRECT.
+ */
+int nfsd_write_io_mode(struct svc_export *exp)
+{
+	if (exp->ex_write_io == NFSD_IO_DEFAULT)
+		return nfsd_io_cache_write;
+	return exp->ex_write_io;
+}
+
 /**
  * nfsd_iter_read - Perform a VFS read using an iterator
  * @rqstp: RPC transaction context
@@ -1300,7 +1332,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	init_sync_kiocb(&kiocb, file);
 
-	switch (nfsd_io_cache_read) {
+	switch (nfsd_read_io_mode(fhp->fh_export)) {
 	case NFSD_IO_BUFFERED:
 		break;
 	case NFSD_IO_DIRECT:
@@ -1654,7 +1686,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (verf)
 		nfsd_copy_write_verifier(verf, nn);
 
-	switch (nfsd_io_cache_write) {
+	switch (nfsd_write_io_mode(exp)) {
 	case NFSD_IO_DIRECT:
 		host_err = nfsd_direct_write(rqstp, fhp, nf, nvecs,
 					     cnt, &kiocb);
@@ -1761,7 +1793,8 @@ __be32 nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		return err;
 
 	file = nf->nf_file;
-	if (file->f_op->splice_read && nfsd_read_splice_ok(rqstp))
+	if (file->f_op->splice_read && nfsd_read_splice_ok(rqstp) &&
+	    nfsd_read_io_mode(fhp->fh_export) == NFSD_IO_BUFFERED)
 		err = nfsd_splice_read(rqstp, fhp, file, offset, count, eof);
 	else
 		err = nfsd_iter_read(rqstp, fhp, nf, offset, count, eof);
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index 1f05c83a3ea6..3cac25adf16b 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -184,6 +184,8 @@ __be32		nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 				struct nfsd_file *nf, loff_t offset,
 				unsigned long *count, u32 *eof);
 bool		nfsd_read_splice_ok(struct svc_rqst *rqstp);
+int		nfsd_read_io_mode(struct svc_export *exp);
+int		nfsd_write_io_mode(struct svc_export *exp);
 __be32		nfsd_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 				loff_t offset, unsigned long *count,
 				u32 *eof);

-- 
2.56.0