netfs: Make deprecated PG_private_2 support opt-in

Make the deprecated PG_private_2 support opt-in, requiring it to be
selected by the filesystems that might want to use it.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260909072105.1663687-7-dhowells@redhat.com
Reviewed-by: Paulo Alcantara <pc@manguebit.org>
cc: Trond Myklebust <trondmy@kernel.org>
cc: Anna Schumaker <anna@kernel.org>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Alex Markuze <amarkuze@redhat.com>
cc: Viacheslav Dubeyko <slava@dubeyko.com>
cc: netfs@lists.linux.dev
cc: linux-nfs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

8 files changed, 39 insertions, 4 deletions

diff --git a/fs/ceph/Kconfig b/fs/ceph/Kconfig
index 3d64a316ca31..aa6ccd7794d2 100644
--- a/fs/ceph/Kconfig
+++ b/fs/ceph/Kconfig
@@ -4,6 +4,7 @@ config CEPH_FS
 	depends on INET
 	select CEPH_LIB
 	select NETFS_SUPPORT
+	select NETFS_PGPRIV2
 	select FS_ENCRYPTION_ALGS if FS_ENCRYPTION
 	default n
 	help
diff --git a/fs/netfs/Kconfig b/fs/netfs/Kconfig
index 7701c037c328..d0e7b0971fa3 100644
--- a/fs/netfs/Kconfig
+++ b/fs/netfs/Kconfig
@@ -22,6 +22,9 @@ config NETFS_STATS
 	  between CPUs.  On the other hand, the stats are very useful for
 	  debugging purposes.  Saying 'Y' here is recommended.
 
+config NETFS_PGPRIV2
+	bool
+
 config NETFS_DEBUG
 	bool "Enable dynamic debugging netfslib and FS-Cache"
 	depends on NETFS_SUPPORT
diff --git a/fs/netfs/Makefile b/fs/netfs/Makefile
index b43188d64bd8..54834cde7e56 100644
--- a/fs/netfs/Makefile
+++ b/fs/netfs/Makefile
@@ -11,7 +11,6 @@ netfs-y := \
 	misc.o \
 	objects.o \
 	read_collect.o \
-	read_pgpriv2.o \
 	read_retry.o \
 	read_single.o \
 	rolling_buffer.o \
@@ -19,6 +18,7 @@ netfs-y := \
 	write_issue.o \
 	write_retry.o
 
+netfs-$(CONFIG_NETFS_PGPRIV2) += read_pgpriv2.o
 netfs-$(CONFIG_NETFS_STATS) += stats.o
 
 netfs-$(CONFIG_FSCACHE) += \
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 61cf82b4b60d..54287a8ef0f8 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -242,7 +242,7 @@ static void netfs_mark_copy_to_cache(struct netfs_io_request *rreq,
 
 		if (overlap > 0 && copy) {
 			folio = folioq_folio(*fq, *slot);
-			if (unlikely(test_bit(NETFS_RREQ_USE_PGPRIV2, &rreq->flags))) {
+			if (netfs_using_pgpriv2(rreq)) {
 				if (!folio_test_private_2(folio))
 					folio_start_private_2(folio);
 			} else {
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index a4c834e32214..3aebe4a4f7b0 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -120,9 +120,37 @@ void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error);
 /*
  * read_pgpriv2.c
  */
+#ifdef CONFIG_NETFS_PGPRIV2
+int netfs_prepare_pgpriv2_write_buffer(struct netfs_io_subrequest *subreq,
+				       unsigned int max_segs);
 void netfs_pgpriv2_copy_to_cache(struct netfs_io_request *rreq, struct folio *folio);
 void netfs_pgpriv2_end_copy_to_cache(struct netfs_io_request *rreq);
 bool netfs_pgpriv2_unlock_copied_folios(struct netfs_io_request *wreq);
+static inline bool netfs_using_pgpriv2(const struct netfs_io_request *rreq)
+{
+	return unlikely(test_bit(NETFS_RREQ_USE_PGPRIV2, &rreq->flags));
+}
+#else
+static inline int netfs_prepare_pgpriv2_write_buffer(struct netfs_io_subrequest *subreq,
+						     unsigned int max_segs)
+{
+	return -EIO;
+}
+static inline void netfs_pgpriv2_copy_to_cache(struct netfs_io_request *rreq, struct folio *folio)
+{
+}
+static inline void netfs_pgpriv2_end_copy_to_cache(struct netfs_io_request *rreq)
+{
+}
+static inline bool netfs_pgpriv2_unlock_copied_folios(struct netfs_io_request *wreq)
+{
+	return true;
+}
+static inline bool netfs_using_pgpriv2(const struct netfs_io_request *rreq)
+{
+	return false;
+}
+#endif
 
 /*
  * read_retry.c
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index 61f2664de6d3..01ea1ddae04b 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -38,7 +38,7 @@ static void netfs_clear_unread(struct netfs_io_subrequest *subreq)
  */
 void netfs_cancel_copy_to_cache(struct netfs_io_request *rreq, struct folio *folio)
 {
-	if (!test_bit(NETFS_RREQ_USE_PGPRIV2, &rreq->flags)) {
+	if (!netfs_using_pgpriv2(rreq)) {
 		if (folio_get_private(folio) == NETFS_FOLIO_COPY_TO_CACHE) {
 			folio_detach_private(folio);
 			trace_netfs_folio(folio, netfs_folio_trace_cancel_copy);
@@ -81,7 +81,7 @@ static void netfs_unlock_read_folio(struct netfs_io_request *rreq,
 	if (unlikely(test_bit(NETFS_RREQ_CANCEL_CACHING, &rreq->flags)))
 		netfs_cancel_copy_to_cache(rreq, folio);
 
-	if (!test_bit(NETFS_RREQ_USE_PGPRIV2, &rreq->flags)) {
+	if (!netfs_using_pgpriv2(rreq)) {
 		if (netfs_folio_group(folio) == NETFS_FOLIO_COPY_TO_CACHE)  {
 			trace_netfs_folio(folio, netfs_folio_trace_sched_copy);
 			folio_mark_dirty(folio);
diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
index 6bb30543eff0..e7862f35b72c 100644
--- a/fs/nfs/Kconfig
+++ b/fs/nfs/Kconfig
@@ -174,6 +174,7 @@ config NFS_FSCACHE
 	bool "Provide NFS client caching support"
 	depends on NFS_FS
 	select NETFS_SUPPORT
+	select NETFS_PGPRIV2
 	select FSCACHE
 	help
 	  Say Y here if you want NFS data to be cached locally on disc through
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index f2b3e61c1891..71fdd6ef43a7 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -279,8 +279,10 @@ struct netfs_io_request {
 #define NETFS_RREQ_UPLOAD_TO_SERVER	11	/* Need to write to the server */
 #define NETFS_RREQ_USE_IO_ITER		12	/* Use ->io_iter rather than ->i_pages */
 #define NETFS_RREQ_NEED_PUT_RA_REFS	17	/* Need to put the folio refs RA gave us */
+#ifdef CONFIG_NETFS_PGPRIV2
 #define NETFS_RREQ_USE_PGPRIV2		31	/* [DEPRECATED] Use PG_private_2 to mark
 						 * write to cache on read */
+#endif
 	const struct netfs_request_ops *netfs_ops;
 };