CIFS: Optimize cifs_user_read() in a short read case on reconnects

by filling the output buffer with a data got from a partially received
response and requesting the remaining data from the server. This is
suitable for non-signed connections.

Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 20 insertions, 3 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index e17012817d9d..5d2501df8f6b 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3030,13 +3030,30 @@ again:
                         else if (rdata->result == -EAGAIN) {
                                 /* resend call if it's a retryable error */
                                 struct list_head tmp_list;
+                                unsigned int got_bytes = rdata->got_bytes;
 
                                 list_del_init(&rdata->list);
                                 INIT_LIST_HEAD(&tmp_list);
 
-                                rc = cifs_send_async_read(rdata->offset,
-                                                rdata->bytes, rdata->cfile,
-                                                cifs_sb, &tmp_list);
+                                /*
+                                 * Got a part of data and then reconnect has
+                                 * happened -- fill the buffer and continue
+                                 * reading.
+                                 */
+                                if (got_bytes && got_bytes < rdata->bytes) {
+                                        rc = cifs_readdata_to_iov(rdata, to);
+                                        if (rc) {
+                                                kref_put(&rdata->refcount,
+                                                cifs_uncached_readdata_release);
+                                                continue;
+                                        }
+                                }
+
+                                rc = cifs_send_async_read(
+                                                rdata->offset + got_bytes,
+                                                rdata->bytes - got_bytes,
+                                                rdata->cfile, cifs_sb,
+                                                &tmp_list);
 
                                 list_splice(&tmp_list, &rdata_list);