cifs: turn read_from_socket into a wrapper around a vectorized version

Eventually we'll want to allow cifsd to read data directly into the
pagecache. In order to do that we'll need a routine that can take a
kvec array and pass that directly to kernel_recvmsg.

Unfortunately though, the kernel's recvmsg routines modify the kvec
array that gets passed in, so we need to use a copy of the kvec array
and refresh that copy on each pass through the loop.

Reviewed-and-Tested-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Jeff Layton <jlayton@redhat.com>

1 files changed, 61 insertions, 7 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 97a65af2a08a..4860940b748b 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -375,14 +375,54 @@ server_unresponsive(struct TCP_Server_Info *server)
         return false;
 }
 
+/*
+ * kvec_array_init - clone a kvec array, and advance into it
+ * @new:        pointer to memory for cloned array
+ * @iov:        pointer to original array
+ * @nr_segs:    number of members in original array
+ * @bytes:      number of bytes to advance into the cloned array
+ *
+ * This function will copy the array provided in iov to a section of memory
+ * and advance the specified number of bytes into the new array. It returns
+ * the number of segments in the new array. "new" must be at least as big as
+ * the original iov array.
+ */
+static unsigned int
+kvec_array_init(struct kvec *new, struct kvec *iov, unsigned int nr_segs,
+                size_t bytes)
+{
+        size_t base = 0;
+
+        while (bytes || !iov->iov_len) {
+                int copy = min(bytes, iov->iov_len);
+
+                bytes -= copy;
+                base += copy;
+                if (iov->iov_len == base) {
+                        iov++;
+                        nr_segs--;
+                        base = 0;
+                }
+        }
+        memcpy(new, iov, sizeof(*iov) * nr_segs);
+        new->iov_base += base;
+        new->iov_len -= base;
+        return nr_segs;
+}
+
 static int
-read_from_socket(struct TCP_Server_Info *server, char *buf,
-                 unsigned int to_read)
+readv_from_socket(struct TCP_Server_Info *server, struct kvec *iov_orig,
+                  unsigned int nr_segs, unsigned int to_read)
 {
         int length = 0;
         int total_read;
+        unsigned int segs;
         struct msghdr smb_msg;
-        struct kvec iov;
+        struct kvec *iov;
+
+        iov = kmalloc(sizeof(*iov_orig) * nr_segs, GFP_NOFS);
+        if (!iov)
+                return -ENOMEM;
 
         smb_msg.msg_control = NULL;
         smb_msg.msg_controllen = 0;
@@ -393,10 +433,11 @@ read_from_socket(struct TCP_Server_Info *server, char *buf,
                         break;
                 }
 
-                iov.iov_base = buf + total_read;
-                iov.iov_len = to_read;
-                length = kernel_recvmsg(server->ssocket, &smb_msg, &iov, 1,
-                                        to_read, 0);
+                segs = kvec_array_init(iov, iov_orig, nr_segs, total_read);
+
+                length = kernel_recvmsg(server->ssocket, &smb_msg,
+                                        iov, segs, to_read, 0);
+
                 if (server->tcpStatus == CifsExiting) {
                         total_read = -ESHUTDOWN;
                         break;
@@ -423,9 +464,22 @@ read_from_socket(struct TCP_Server_Info *server, char *buf,
                         break;
                 }
         }
+        kfree(iov);
         return total_read;
 }
 
+static int
+read_from_socket(struct TCP_Server_Info *server, char *buf,
+                 unsigned int to_read)
+{
+        struct kvec iov;
+
+        iov.iov_base = buf;
+        iov.iov_len = to_read;
+
+        return readv_from_socket(server, &iov, 1, to_read);
+}
+
 static bool
 is_smb_response(struct TCP_Server_Info *server, unsigned char type)
 {