cifs: Add support for root file systems (8eecd1c2) · Commits · 戴 / test

Documentation/filesystems/cifs/cifsroot.txt

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			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

fs/cifs/Kconfig

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	@@ -211,3 +211,11 @@ config CIFS_FSCACHE
	Makes CIFS FS-Cache capable. Say Y here if you want your CIFS data		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		to be cached locally on disk through the general filesystem cache
	manager. If unsure, say N.		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.

fs/cifs/Makefile

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	@@ -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_FSCACHE) += fscache.o cache.o

	cifs-$(CONFIG_CIFS_SMB_DIRECT) += smbdirect.o		cifs-$(CONFIG_CIFS_SMB_DIRECT) += smbdirect.o

			cifs-$(CONFIG_CIFS_ROOT) += cifsroot.o

fs/cifs/cifsglob.h

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	@@ -607,6 +607,7 @@ struct smb_vol {
	__u32 handle_timeout; /* persistent and durable handle timeout in ms */		__u32 handle_timeout; /* persistent and durable handle timeout in ms */
	unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */		unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */
	__u16 compression; /* compression algorithm 0xFFFF default 0=disabled */		__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.		* reconnect.
	*/		*/
	int nr_targets;		int nr_targets;
			bool noblockcnt; /* use non-blocking connect() */
	};		};

	struct cifs_credits {		struct cifs_credits {

fs/cifs/cifsroot.c

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			// 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;
			}

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