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, 66 insertions, 0 deletions

diff --git a/Documentation/admin-guide/jfs.rst b/Documentation/admin-guide/jfs.rst
new file mode 100644
index 000000000..9e12d936b
--- /dev/null
+++ b/Documentation/admin-guide/jfs.rst
@@ -0,0 +1,66 @@
+===========================================
+IBM's Journaled File System (JFS) for Linux
+===========================================
+
+JFS Homepage:  http://jfs.sourceforge.net/
+
+The following mount options are supported:
+
+(*) == default
+
+iocharset=name
+                Character set to use for converting from Unicode to
+		ASCII.  The default is to do no conversion.  Use
+		iocharset=utf8 for UTF-8 translations.  This requires
+		CONFIG_NLS_UTF8 to be set in the kernel .config file.
+		iocharset=none specifies the default behavior explicitly.
+
+resize=value
+                Resize the volume to <value> blocks.  JFS only supports
+		growing a volume, not shrinking it.  This option is only
+		valid during a remount, when the volume is mounted
+		read-write.  The resize keyword with no value will grow
+		the volume to the full size of the partition.
+
+nointegrity
+                Do not write to the journal.  The primary use of this option
+		is to allow for higher performance when restoring a volume
+		from backup media.  The integrity of the volume is not
+		guaranteed if the system abnormally abends.
+
+integrity(*)
+                Commit metadata changes to the journal.  Use this option to
+		remount a volume where the nointegrity option was
+		previously specified in order to restore normal behavior.
+
+errors=continue
+                        Keep going on a filesystem error.
+errors=remount-ro(*)
+                        Remount the filesystem read-only on an error.
+errors=panic
+                        Panic and halt the machine if an error occurs.
+
+uid=value
+                Override on-disk uid with specified value
+gid=value
+                Override on-disk gid with specified value
+umask=value
+                Override on-disk umask with specified octal value. For
+                directories, the execute bit will be set if the corresponding
+		read bit is set.
+
+discard=minlen, discard/nodiscard(*)
+                This enables/disables the use of discard/TRIM commands.
+		The discard/TRIM commands are sent to the underlying
+                block device when blocks are freed. This is useful for SSD
+                devices and sparse/thinly-provisioned LUNs.  The FITRIM ioctl
+		command is also available together with the nodiscard option.
+		The value of minlen specifies the minimum blockcount, when
+		a TRIM command to the block device is considered useful.
+		When no value is given to the discard option, it defaults to
+		64 blocks, which means 256KiB in JFS.
+		The minlen value of discard overrides the minlen value given
+		on an FITRIM ioctl().
+
+The JFS mailing list can be subscribed to by using the link labeled
+"Mail list Subscribe" at our web page http://jfs.sourceforge.net/