netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 65 insertions, 0 deletions

diff --git a/fs/pnode.h b/fs/pnode.h
new file mode 100644
index 000000000..b029db225
--- /dev/null
+++ b/fs/pnode.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/fs/pnode.h
+ *
+ * (C) Copyright IBM Corporation 2005.
+ */
+#ifndef _LINUX_PNODE_H
+#define _LINUX_PNODE_H
+
+#include <linux/list.h>
+#include "mount.h"
+
+#define IS_MNT_SHARED(m) ((m)->mnt_t_flags & T_SHARED)
+#define IS_MNT_SLAVE(m) ((m)->mnt_master)
+#define IS_MNT_NEW(m) (!(m)->mnt_ns)
+#define CLEAR_MNT_SHARED(m) ((m)->mnt_t_flags &= ~T_SHARED)
+#define IS_MNT_UNBINDABLE(m) ((m)->mnt_t_flags & T_UNBINDABLE)
+#define IS_MNT_MARKED(m) ((m)->mnt_t_flags & T_MARKED)
+#define SET_MNT_MARK(m) ((m)->mnt_t_flags |= T_MARKED)
+#define CLEAR_MNT_MARK(m) ((m)->mnt_t_flags &= ~T_MARKED)
+#define IS_MNT_LOCKED(m) ((m)->mnt.mnt_flags & MNT_LOCKED)
+
+#define CL_EXPIRE    		0x01
+#define CL_SLAVE     		0x02
+#define CL_COPY_UNBINDABLE	0x04
+#define CL_MAKE_SHARED 		0x08
+#define CL_PRIVATE 		0x10
+#define CL_COPY_MNT_NS_FILE	0x40
+
+/*
+ * EXCL[namespace_sem]
+ */
+static inline void set_mnt_shared(struct mount *mnt)
+{
+	mnt->mnt_t_flags &= ~T_SHARED_MASK;
+	mnt->mnt_t_flags |= T_SHARED;
+}
+
+static inline bool peers(const struct mount *m1, const struct mount *m2)
+{
+	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
+}
+
+void change_mnt_propagation(struct mount *, int);
+void bulk_make_private(struct list_head *);
+int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
+		struct hlist_head *);
+void propagate_umount(struct list_head *);
+int propagate_mount_busy(struct mount *, int);
+void propagate_mount_unlock(struct mount *);
+void mnt_release_group_id(struct mount *);
+int get_dominating_id(struct mount *mnt, const struct path *root);
+int mnt_get_count(struct mount *mnt);
+void mnt_set_mountpoint(struct mount *, struct mountpoint *,
+			struct mount *);
+void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp,
+			   struct mount *mnt);
+struct mount *copy_tree(struct mount *, struct dentry *, int);
+bool is_path_reachable(struct mount *, struct dentry *,
+			 const struct path *root);
+int count_mounts(struct mnt_namespace *ns, struct mount *mnt);
+bool propagation_would_overmount(const struct mount *from,
+				 const struct mount *to,
+				 const struct mountpoint *mp);
+#endif /* _LINUX_PNODE_H */