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, 68 insertions, 0 deletions

diff --git a/Documentation/admin-guide/ufs.rst b/Documentation/admin-guide/ufs.rst
new file mode 100644
index 000000000..55d15297f
--- /dev/null
+++ b/Documentation/admin-guide/ufs.rst
@@ -0,0 +1,68 @@
+=========
+Using UFS
+=========
+
+mount -t ufs -o ufstype=type_of_ufs device dir
+
+
+UFS Options
+===========
+
+ufstype=type_of_ufs
+	UFS is a file system widely used in different operating systems.
+	The problem are differences among implementations. Features of
+	some implementations are undocumented, so its hard to recognize
+	type of ufs automatically. That's why user must specify type of
+	ufs manually by mount option ufstype. Possible values are:
+
+	old
+                old format of ufs
+		default value, supported as read-only
+
+	44bsd
+                used in FreeBSD, NetBSD, OpenBSD
+		supported as read-write
+
+	ufs2
+                used in FreeBSD 5.x
+		supported as read-write
+
+	5xbsd
+                synonym for ufs2
+
+	sun
+                used in SunOS (Solaris)
+		supported as read-write
+
+	sunx86
+                used in SunOS for Intel (Solarisx86)
+		supported as read-write
+
+	hp
+                used in HP-UX
+		supported as read-only
+
+	nextstep
+		used in NextStep
+		supported as read-only
+
+	nextstep-cd
+		used for NextStep CDROMs (block_size == 2048)
+		supported as read-only
+
+	openstep
+		used in OpenStep
+		supported as read-only
+
+
+Possible Problems
+-----------------
+
+See next section, if you have any.
+
+
+Bug Reports
+-----------
+
+Any ufs bug report you can send to daniel.pirkl@email.cz or
+to dushistov@mail.ru (do not send partition tables bug reports).