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, 86 insertions, 0 deletions

diff --git a/drivers/comedi/comedi_internal.h b/drivers/comedi/comedi_internal.h
new file mode 100644
index 000000000..41a3b09f8
--- /dev/null
+++ b/drivers/comedi/comedi_internal.h
@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _COMEDI_INTERNAL_H
+#define _COMEDI_INTERNAL_H
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+/*
+ * various internal comedi stuff
+ */
+
+struct comedi_buf_map;
+struct comedi_devconfig;
+struct comedi_device;
+struct comedi_insn;
+struct comedi_rangeinfo;
+struct comedi_subdevice;
+struct device;
+
+int do_rangeinfo_ioctl(struct comedi_device *dev,
+		       struct comedi_rangeinfo *it);
+struct comedi_device *comedi_alloc_board_minor(struct device *hardware_device);
+void comedi_release_hardware_device(struct device *hardware_device);
+int comedi_alloc_subdevice_minor(struct comedi_subdevice *s);
+void comedi_free_subdevice_minor(struct comedi_subdevice *s);
+
+int comedi_buf_alloc(struct comedi_device *dev, struct comedi_subdevice *s,
+		     unsigned long new_size);
+void comedi_buf_reset(struct comedi_subdevice *s);
+bool comedi_buf_is_mmapped(struct comedi_subdevice *s);
+void comedi_buf_map_get(struct comedi_buf_map *bm);
+int comedi_buf_map_put(struct comedi_buf_map *bm);
+int comedi_buf_map_access(struct comedi_buf_map *bm, unsigned long offset,
+			  void *buf, int len, int write);
+struct comedi_buf_map *
+comedi_buf_map_from_subdev_get(struct comedi_subdevice *s);
+unsigned int comedi_buf_write_n_available(struct comedi_subdevice *s);
+unsigned int comedi_buf_write_n_allocated(struct comedi_subdevice *s);
+unsigned int _comedi_buf_write_alloc(struct comedi_subdevice *s,
+				     unsigned int nbytes);
+unsigned int _comedi_buf_write_free(struct comedi_subdevice *s,
+				    unsigned int nbytes);
+unsigned int _comedi_buf_read_n_available(struct comedi_subdevice *s);
+unsigned int _comedi_buf_read_alloc(struct comedi_subdevice *s,
+				    unsigned int nbytes);
+unsigned int _comedi_buf_read_free(struct comedi_subdevice *s,
+				   unsigned int nbytes);
+void _comedi_inc_scan_progress(struct comedi_subdevice *s,
+			       unsigned int num_bytes);
+void _comedi_event(struct comedi_device *dev, struct comedi_subdevice *s);
+void comedi_device_cancel_all(struct comedi_device *dev);
+bool comedi_can_auto_free_spriv(struct comedi_subdevice *s);
+
+extern unsigned int comedi_default_buf_size_kb;
+extern unsigned int comedi_default_buf_maxsize_kb;
+
+/* drivers.c */
+
+extern struct comedi_driver *comedi_drivers;
+extern struct mutex comedi_drivers_list_lock;
+
+int insn_inval(struct comedi_device *dev, struct comedi_subdevice *s,
+	       struct comedi_insn *insn, unsigned int *data);
+
+void comedi_device_detach_locked(struct comedi_device *dev);
+void comedi_device_detach(struct comedi_device *dev);
+int comedi_device_attach(struct comedi_device *dev,
+			 struct comedi_devconfig *it);
+
+#ifdef CONFIG_PROC_FS
+
+/* proc.c */
+
+void comedi_proc_init(void);
+void comedi_proc_cleanup(void);
+#else
+static inline void comedi_proc_init(void)
+{
+}
+
+static inline void comedi_proc_cleanup(void)
+{
+}
+#endif
+
+#endif /* _COMEDI_INTERNAL_H */