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, 28 insertions, 0 deletions

diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
new file mode 100644
index 000000000..c6a063a54
--- /dev/null
+++ b/drivers/tty/Makefile
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_TTY)		+= tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
+				   tty_buffer.o tty_port.o tty_mutex.o \
+				   tty_ldsem.o tty_baudrate.o tty_jobctrl.o \
+				   n_null.o
+obj-$(CONFIG_LEGACY_PTYS)	+= pty.o
+obj-$(CONFIG_UNIX98_PTYS)	+= pty.o
+obj-$(CONFIG_AUDIT)		+= tty_audit.o
+obj-$(CONFIG_MAGIC_SYSRQ)	+= sysrq.o
+obj-$(CONFIG_N_HDLC)		+= n_hdlc.o
+obj-$(CONFIG_N_GSM)		+= n_gsm.o
+
+obj-y				+= vt/
+obj-$(CONFIG_HVC_DRIVER)	+= hvc/
+obj-y				+= serial/
+obj-$(CONFIG_SERIAL_DEV_BUS)	+= serdev/
+
+# tty drivers
+obj-$(CONFIG_AMIGA_BUILTIN_SERIAL) += amiserial.o
+obj-$(CONFIG_MOXA_INTELLIO)	+= moxa.o
+obj-$(CONFIG_MOXA_SMARTIO)	+= mxser.o
+obj-$(CONFIG_NOZOMI)		+= nozomi.o
+obj-$(CONFIG_NULL_TTY)	        += ttynull.o
+obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o
+obj-$(CONFIG_GOLDFISH_TTY)	+= goldfish.o
+obj-$(CONFIG_MIPS_EJTAG_FDC_TTY) += mips_ejtag_fdc.o
+obj-$(CONFIG_VCC)		+= vcc.o
+obj-$(CONFIG_RPMSG_TTY)		+= rpmsg_tty.o