cifs: Add support for root file systems

Introduce a new CONFIG_CIFS_ROOT option to handle root file systems
over a SMB share.

In order to mount the root file system during the init process, make
cifs.ko perform non-blocking socket operations while mounting and
accessing it.

Cc: Steve French <smfrench@gmail.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Paulo Alcantara (SUSE) <paulo@paulo.ac>
Signed-off-by: Steve French <stfrench@microsoft.com>

5 files changed, 109 insertions, 3 deletions

diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
index b16219e5dac9..99a22e57660e 100644
--- a/fs/cifs/Kconfig
+++ b/fs/cifs/Kconfig
@@ -211,3 +211,11 @@ config CIFS_FSCACHE
 	  Makes CIFS FS-Cache capable. Say Y here if you want your CIFS data
 	  to be cached locally on disk through the general filesystem cache
 	  manager. If unsure, say N.
+
+config CIFS_ROOT
+	bool "SMB root file system (Experimental)"
+	depends on CIFS=y && IP_PNP
+	help
+	  Enables root file system support over SMB protocol.
+
+	  Most people say N here.
diff --git a/fs/cifs/Makefile b/fs/cifs/Makefile
index 41332f20055b..51bae9340842 100644
--- a/fs/cifs/Makefile
+++ b/fs/cifs/Makefile
@@ -21,3 +21,5 @@ cifs-$(CONFIG_CIFS_DFS_UPCALL) += dns_resolve.o cifs_dfs_ref.o dfs_cache.o
 cifs-$(CONFIG_CIFS_FSCACHE) += fscache.o cache.o
 
 cifs-$(CONFIG_CIFS_SMB_DIRECT) += smbdirect.o
+
+cifs-$(CONFIG_CIFS_ROOT) += cifsroot.o
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 09b60ec5de3e..54e204589cb9 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -607,6 +607,7 @@ struct smb_vol {
 	__u32 handle_timeout; /* persistent and durable handle timeout in ms */
 	unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */
 	__u16 compression; /* compression algorithm 0xFFFF default 0=disabled */
+	bool rootfs:1; /* if it's a SMB root file system */
 };
 
 /**
@@ -764,6 +765,7 @@ struct TCP_Server_Info {
 	 * reconnect.
 	 */
 	int nr_targets;
+	bool noblockcnt; /* use non-blocking connect() */
 };
 
 struct cifs_credits {
diff --git a/fs/cifs/cifsroot.c b/fs/cifs/cifsroot.c
new file mode 100644
index 000000000000..8760d9cbf25e
--- /dev/null
+++ b/fs/cifs/cifsroot.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SMB root file system support
+ *
+ * Copyright (c) 2019 Paulo Alcantara <palcantara@suse.de>
+ */
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/root_dev.h>
+#include <linux/kernel.h>
+#include <linux/in.h>
+#include <linux/inet.h>
+#include <net/ipconfig.h>
+
+#define DEFAULT_MNT_OPTS \
+	"vers=1.0,cifsacl,mfsymlinks,rsize=1048576,wsize=65536,uid=0,gid=0," \
+	"hard,rootfs"
+
+static char root_dev[2048] __initdata = "";
+static char root_opts[1024] __initdata = DEFAULT_MNT_OPTS;
+
+static __be32 __init parse_srvaddr(char *start, char *end)
+{
+	char addr[sizeof("aaa.bbb.ccc.ddd")];
+	int i = 0;
+
+	while (start < end && i < sizeof(addr) - 1) {
+		if (isdigit(*start) || *start == '.')
+			addr[i++] = *start;
+		start++;
+	}
+	addr[i] = '\0';
+	return in_aton(addr);
+}
+
+/* cifsroot=//<server-ip>/<share>[,options] */
+static int __init cifs_root_setup(char *line)
+{
+	char *s;
+	int len;
+	__be32 srvaddr = htonl(INADDR_NONE);
+
+	ROOT_DEV = Root_CIFS;
+
+	if (strlen(line) > 3 && line[0] == '/' && line[1] == '/') {
+		s = strchr(&line[2], '/');
+		if (!s || s[1] == '\0')
+			return 1;
+
+		s = strchrnul(s, ',');
+		len = s - line + 1;
+		if (len <= sizeof(root_dev)) {
+			strlcpy(root_dev, line, len);
+			srvaddr = parse_srvaddr(&line[2], s);
+			if (*s) {
+				snprintf(root_opts, sizeof(root_opts), "%s,%s",
+					 DEFAULT_MNT_OPTS, s + 1);
+			}
+		}
+	}
+
+	root_server_addr = srvaddr;
+
+	return 1;
+}
+
+__setup("cifsroot=", cifs_root_setup);
+
+int __init cifs_root_data(char **dev, char **opts)
+{
+	if (!root_dev[0] || root_server_addr == htonl(INADDR_NONE)) {
+		printk(KERN_ERR "Root-CIFS: no SMB server address\n");
+		return -1;
+	}
+
+	*dev = root_dev;
+	*opts = root_opts;
+
+	return 0;
+}
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index e16b6cc1e31b..2850c3ce4391 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -96,7 +96,7 @@ enum {
 	Opt_multiuser, Opt_sloppy, Opt_nosharesock,
 	Opt_persistent, Opt_nopersistent,
 	Opt_resilient, Opt_noresilient,
-	Opt_domainauto, Opt_rdma, Opt_modesid,
+	Opt_domainauto, Opt_rdma, Opt_modesid, Opt_rootfs,
 	Opt_compress,
 
 	/* Mount options which take numeric value */
@@ -266,6 +266,7 @@ static const match_table_t cifs_mount_option_tokens = {
 	{ Opt_ignore, "nomand" },
 	{ Opt_ignore, "relatime" },
 	{ Opt_ignore, "_netdev" },
+	{ Opt_rootfs, "rootfs" },
 
 	{ Opt_err, NULL }
 };
@@ -1777,6 +1778,11 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 		case Opt_nodfs:
 			vol->nodfs = 1;
 			break;
+		case Opt_rootfs:
+#ifdef CONFIG_CIFS_ROOT
+			vol->rootfs = true;
+#endif
+			break;
 		case Opt_posixpaths:
 			vol->posix_paths = 1;
 			break;
@@ -2727,7 +2733,8 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
 		goto out_err_crypto_release;
 	}
 
-	tcp_ses->noblocksnd = volume_info->noblocksnd;
+	tcp_ses->noblockcnt = volume_info->rootfs;
+	tcp_ses->noblocksnd = volume_info->noblocksnd || volume_info->rootfs;
 	tcp_ses->noautotune = volume_info->noautotune;
 	tcp_ses->tcp_nodelay = volume_info->sockopt_tcp_nodelay;
 	tcp_ses->rdma = volume_info->rdma;
@@ -3873,7 +3880,11 @@ generic_ip_connect(struct TCP_Server_Info *server)
 		 socket->sk->sk_sndbuf,
 		 socket->sk->sk_rcvbuf, socket->sk->sk_rcvtimeo);
 
-	rc = socket->ops->connect(socket, saddr, slen, 0);
+	rc = socket->ops->connect(socket, saddr, slen,
+				  server->noblockcnt ? O_NONBLOCK : 0);
+
+	if (rc == -EINPROGRESS)
+		rc = 0;
 	if (rc < 0) {
 		cifs_dbg(FYI, "Error %d connecting to server\n", rc);
 		sock_release(socket);