cifs: Only pick a channel once per read request

In cifs, only pick a channel when setting up a read request rather than
doing so individually for every subrequest and instead use that channel for
all.  This mirrors what the code in v6.9 does.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: dhowells

fs/smb/client/cifsglob.h

@@ -1494,6 +1494,7 @@ struct cifs_aio_ctx {
 struct cifs_io_request {
 	struct netfs_io_request		rreq;
 	struct cifsFileInfo		*cfile;
+	struct TCP_Server_Info		*server;
 };
 
 /* asynchronous read support */

fs/smb/client/file.c

@@ -134,17 +134,15 @@ static void cifs_issue_write(struct netfs_io_subrequest *subreq)
 static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *rreq = subreq->rreq;
-	struct TCP_Server_Info *server;
 	struct cifs_io_subrequest *rdata = container_of(subreq, struct cifs_io_subrequest, subreq);
 	struct cifs_io_request *req = container_of(subreq->rreq, struct cifs_io_request, rreq);
+	struct TCP_Server_Info *server = req->server;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(rreq->inode->i_sb);
 	size_t rsize = 0;
 	int rc;
 
 	rdata->xid = get_xid();
 	rdata->have_xid = true;
-
-	server = cifs_pick_channel(tlink_tcon(req->cfile->tlink)->ses);
 	rdata->server = server;
 
 	if (cifs_sb->ctx->rsize == 0)
@@ -203,14 +201,7 @@ static void cifs_req_issue_read(struct netfs_io_subrequest *subreq)
 	__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
 	rdata->pid = pid;
 
-	rc = adjust_credits(rdata->server, &rdata->credits, rdata->subreq.len);
-	if (!rc) {
-		if (rdata->req->cfile->invalidHandle)
-			rc = -EAGAIN;
-		else
-			rc = rdata->server->ops->async_readv(rdata);
-	}
-
+	rc = rdata->server->ops->async_readv(rdata);
 out:
 	if (rc)
 		netfs_subreq_terminated(subreq, rc, false);
@@ -250,6 +241,7 @@ static int cifs_init_request(struct netfs_io_request *rreq, struct file *file)
 		open_file = file->private_data;
 		rreq->netfs_priv = file->private_data;
 		req->cfile = cifsFileInfo_get(open_file);
+		req->server = cifs_pick_channel(tlink_tcon(req->cfile->tlink)->ses);
 	} else if (rreq->origin != NETFS_WRITEBACK) {
 		WARN_ON_ONCE(1);
 		return -EIO;