cifs: Fix handling of a beyond-EOF DIO/unbuffered read over SMB2

If a DIO read or an unbuffered read request extends beyond the EOF, the
server will return a short read and a status code indicating that EOF was
hit, which gets translated to -ENODATA. Note that the client does not cap
the request at i_size, but asks for the amount requested in case there's a
race on the server with a third party.

Now, on the client side, the request will get split into multiple
subrequests if rsize is smaller than the full request size. A subrequest
that starts before or at the EOF and returns short data up to the EOF will
be correctly handled, with the NETFS_SREQ_HIT_EOF flag being set,
indicating to netfslib that we can't read more.

If a subrequest, however, starts after the EOF and not at it, HIT_EOF will
not be flagged, its error will be set to -ENODATA and it will be abandoned.
This will cause the request as a whole to fail with -ENODATA.

Fix this by setting NETFS_SREQ_HIT_EOF on any subrequest that lies beyond
the EOF marker.

Fixes: 1da29f2c39b6 ("netfs, cifs: Fix handling of short DIO read")
Signed-off-by: David Howells <[e-mail]>
Reviewed-by: Paulo Alcantara (Red Hat) <[e-mail]>
cc: Shyam Prasad N <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
Signed-off-by: Steve French <[e-mail]>

fs/smb/client/smb2pdu.c

···
 	} else {
 		size_t trans = rdata->subreq.transferred + rdata->got_bytes;
 		if (trans < rdata->subreq.len &&
-		    rdata->subreq.start + trans == ictx->remote_i_size) {
+		    rdata->subreq.start + trans >= ictx->remote_i_size) {
 			__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
 			rdata->result = 0;
 		}