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Subject[PATCH 1/3] cifs: Add support for root file systems
Date
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>
Signed-off-by: Paulo Alcantara (SUSE) <paulo@paulo.ac>
---
Documentation/filesystems/cifs/cifsroot.txt | 97 +++++++++++++++++++++
fs/cifs/Kconfig | 8 ++
fs/cifs/Makefile | 2 +
fs/cifs/cifsglob.h | 2 +
fs/cifs/cifsroot.c | 83 ++++++++++++++++++
fs/cifs/connect.c | 17 +++-
include/linux/root_dev.h | 1 +
7 files changed, 207 insertions(+), 3 deletions(-)
create mode 100644 Documentation/filesystems/cifs/cifsroot.txt
create mode 100644 fs/cifs/cifsroot.c

diff --git a/Documentation/filesystems/cifs/cifsroot.txt b/Documentation/filesystems/cifs/cifsroot.txt
new file mode 100644
index 000000000000..0fa1a2c36a40
--- /dev/null
+++ b/Documentation/filesystems/cifs/cifsroot.txt
@@ -0,0 +1,97 @@
+Mounting root file system via SMB (cifs.ko)
+===========================================
+
+Written 2019 by Paulo Alcantara <palcantara@suse.de>
+Written 2019 by Aurelien Aptel <aaptel@suse.com>
+
+The CONFIG_CIFS_ROOT option enables experimental root file system
+support over the SMB protocol via cifs.ko.
+
+It introduces a new kernel command-line option called 'cifsroot='
+which will tell the kernel to mount the root file system over the
+network by utilizing SMB or CIFS protocol.
+
+In order to mount, the network stack will also need to be set up by
+using 'ip=' config option. For more details, see
+Documentation/filesystems/nfs/nfsroot.txt.
+
+A CIFS root mount currently requires the use of SMB1+UNIX Extensions
+which is only supported by the Samba server. SMB1 is the older
+deprecated version of the protocol but it has been extended to support
+POSIX features (See [1]). The equivalent extensions for the newer
+recommended version of the protocol (SMB3) have not been fully
+implemented yet which means SMB3 doesn't support some required POSIX
+file system objects (e.g. block devices, pipes, sockets).
+
+As a result, a CIFS root will default to SMB1 for now but the version
+to use can nonetheless be changed via the 'vers=' mount option. This
+default will change once the SMB3 POSIX extensions are fully
+implemented.
+
+Server configuration
+====================
+
+To enable SMB1+UNIX extensions you will need to set these global
+settings in Samba smb.conf:
+
+ [global]
+ server min protocol = NT1
+ unix extension = yes # default
+
+Kernel command line
+===================
+
+root=/dev/cifs
+
+This is just a virtual device that basically tells the kernel to mount
+the root file system via SMB protocol.
+
+cifsroot=//<server-ip>/<share>[,options]
+
+Enables the kernel to mount the root file system via SMB that are
+located in the <server-ip> and <share> specified in this option.
+
+The default mount options are set in fs/cifs/cifsroot.c.
+
+server-ip
+ IPv4 address of the server.
+
+share
+ Path to SMB share (rootfs).
+
+options
+ Optional mount options. For more information, see mount.cifs(8).
+
+Examples
+========
+
+Export root file system as a Samba share in smb.conf file.
+
+...
+[linux]
+ path = /path/to/rootfs
+ read only = no
+ guest ok = yes
+ force user = root
+ force group = root
+ browseable = yes
+ writeable = yes
+ admin users = root
+ public = yes
+ create mask = 0777
+ directory mask = 0777
+...
+
+Restart smb service.
+
+# systemctl restart smb
+
+Test it under QEMU on a kernel built with CONFIG_CIFS_ROOT and
+CONFIG_IP_PNP options enabled.
+
+# qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \
+ -kernel /path/to/linux/arch/x86/boot/bzImage -nographic \
+ -append "root=/dev/cifs rw ip=dhcp cifsroot=//10.0.2.2/linux,username=foo,password=bar console=ttyS0 3"
+
+
+1: https://wiki.samba.org/index.php/UNIX_Extensions
diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
index 523e9ea78a28..d28d62532318 100644
--- a/fs/cifs/Kconfig
+++ b/fs/cifs/Kconfig
@@ -217,3 +217,11 @@ 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 51af69a1a328..45cf67f37487 100644
--- a/fs/cifs/Makefile
+++ b/fs/cifs/Makefile
@@ -22,3 +22,5 @@ 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 4777b3c4a92c..ac7e433a5b94 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -600,6 +600,7 @@ struct smb_vol {
__u64 snapshot_time; /* needed for timewarp tokens */
__u32 handle_timeout; /* persistent and durable handle timeout in ms */
unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */
+ bool rootfs:1; /* if it's a SMB root file system */
};

/**
@@ -752,6 +753,7 @@ 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 714a359c7c8d..ca6b04af727f 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_domainauto, Opt_rdma, Opt_rootfs,

/* Mount options which take numeric value */
Opt_backupuid, Opt_backupgid, Opt_uid,
@@ -259,6 +259,7 @@ static const match_table_t cifs_mount_option_tokens = {
{ Opt_ignore, "nomand" },
{ Opt_ignore, "relatime" },
{ Opt_ignore, "_netdev" },
+ { Opt_rootfs, "rootfs" },

{ Opt_err, NULL }
};
@@ -1744,6 +1745,11 @@ 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;
@@ -2662,7 +2668,8 @@ 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;
@@ -3768,7 +3775,11 @@ 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);
diff --git a/include/linux/root_dev.h b/include/linux/root_dev.h
index bab671b0782f..4e78651371ba 100644
--- a/include/linux/root_dev.h
+++ b/include/linux/root_dev.h
@@ -8,6 +8,7 @@

enum {
Root_NFS = MKDEV(UNNAMED_MAJOR, 255),
+ Root_CIFS = MKDEV(UNNAMED_MAJOR, 254),
Root_RAM0 = MKDEV(RAMDISK_MAJOR, 0),
Root_RAM1 = MKDEV(RAMDISK_MAJOR, 1),
Root_FD0 = MKDEV(FLOPPY_MAJOR, 0),
--
2.22.0
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