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, 19 insertions, 0 deletions

diff --git a/drivers/bcma/README b/drivers/bcma/README
new file mode 100644
index 000000000..f7e7ce46c
--- /dev/null
+++ b/drivers/bcma/README
@@ -0,0 +1,19 @@
+Broadcom introduced new bus as replacement for older SSB. It is based on AMBA,
+however from programming point of view there is nothing AMBA specific we use.
+
+Standard AMBA drivers are platform specific, have hardcoded addresses and use
+AMBA standard fields like CID and PID.
+
+In case of Broadcom's cards every device consists of:
+1) Broadcom specific AMBA device. It is put on AMBA bus, but can not be treated
+   as standard AMBA device. Reading it's CID or PID can cause machine lockup.
+2) AMBA standard devices called ports or wrappers. They have CIDs (AMBA_CID)
+   and PIDs (0x103BB369), but we do not use that info for anything. One of that
+   devices is used for managing Broadcom specific core.
+
+Addresses of AMBA devices are not hardcoded in driver and have to be read from
+EPROM.
+
+In this situation we decided to introduce separated bus. It can contain up to
+16 devices identified by Broadcom specific fields: manufacturer, id, revision
+and class.