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, 52 insertions, 0 deletions

diff --git a/Documentation/driver-api/target.rst b/Documentation/driver-api/target.rst
new file mode 100644
index 000000000..c70ca2517
--- /dev/null
+++ b/Documentation/driver-api/target.rst
@@ -0,0 +1,52 @@
+=================================
+target and iSCSI Interfaces Guide
+=================================
+
+Introduction and Overview
+=========================
+
+TBD
+
+Target core device interfaces
+=============================
+
+This section is blank because no kerneldoc comments have been added to
+drivers/target/target_core_device.c.
+
+Target core transport interfaces
+================================
+
+.. kernel-doc:: drivers/target/target_core_transport.c
+    :export:
+
+Target-supported userspace I/O
+==============================
+
+.. kernel-doc:: drivers/target/target_core_user.c
+    :doc: Userspace I/O
+
+.. kernel-doc:: include/uapi/linux/target_core_user.h
+    :doc: Ring Design
+
+iSCSI helper functions
+======================
+
+.. kernel-doc:: drivers/scsi/libiscsi.c
+   :export:
+
+
+iSCSI boot information
+======================
+
+.. kernel-doc:: drivers/scsi/iscsi_boot_sysfs.c
+   :export:
+
+iSCSI TCP interfaces
+====================
+
+.. kernel-doc:: drivers/scsi/iscsi_tcp.c
+   :internal:
+
+.. kernel-doc:: drivers/scsi/libiscsi_tcp.c
+   :export:
+