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>
This commit is contained in:
Paulo Alcantara (SUSE)
Steve French
parent
0892ba693f
commit
8eecd1c2e5
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@ -0,0 +1,97 @@
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Mounting root file system via SMB (cifs.ko)
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===========================================
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Written 2019 by Paulo Alcantara <palcantara@suse.de>
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Written 2019 by Aurelien Aptel <aaptel@suse.com>
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The CONFIG_CIFS_ROOT option enables experimental root file system
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support over the SMB protocol via cifs.ko.
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It introduces a new kernel command-line option called 'cifsroot='
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which will tell the kernel to mount the root file system over the
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network by utilizing SMB or CIFS protocol.
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In order to mount, the network stack will also need to be set up by
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using 'ip=' config option. For more details, see
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Documentation/filesystems/nfs/nfsroot.txt.
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A CIFS root mount currently requires the use of SMB1+UNIX Extensions
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which is only supported by the Samba server. SMB1 is the older
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deprecated version of the protocol but it has been extended to support
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POSIX features (See [1]). The equivalent extensions for the newer
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recommended version of the protocol (SMB3) have not been fully
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implemented yet which means SMB3 doesn't support some required POSIX
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file system objects (e.g. block devices, pipes, sockets).
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As a result, a CIFS root will default to SMB1 for now but the version
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to use can nonetheless be changed via the 'vers=' mount option. This
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default will change once the SMB3 POSIX extensions are fully
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implemented.
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Server configuration
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====================
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To enable SMB1+UNIX extensions you will need to set these global
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settings in Samba smb.conf:
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[global]
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server min protocol = NT1
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unix extension = yes # default
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Kernel command line
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===================
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root=/dev/cifs
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This is just a virtual device that basically tells the kernel to mount
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the root file system via SMB protocol.
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cifsroot=//<server-ip>/<share>[,options]
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Enables the kernel to mount the root file system via SMB that are
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located in the <server-ip> and <share> specified in this option.
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The default mount options are set in fs/cifs/cifsroot.c.
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server-ip
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IPv4 address of the server.
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share
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Path to SMB share (rootfs).
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options
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Optional mount options. For more information, see mount.cifs(8).
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Examples
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========
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Export root file system as a Samba share in smb.conf file.
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...
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[linux]
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path = /path/to/rootfs
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read only = no
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guest ok = yes
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force user = root
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force group = root
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browseable = yes
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writeable = yes
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admin users = root
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public = yes
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create mask = 0777
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directory mask = 0777
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...
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Restart smb service.
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# systemctl restart smb
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Test it under QEMU on a kernel built with CONFIG_CIFS_ROOT and
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CONFIG_IP_PNP options enabled.
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# qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \
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-kernel /path/to/linux/arch/x86/boot/bzImage -nographic \
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-append "root=/dev/cifs rw ip=dhcp cifsroot=//10.0.2.2/linux,username=foo,password=bar console=ttyS0 3"
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1: https://wiki.samba.org/index.php/UNIX_Extensions
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@ -211,3 +211,11 @@ config CIFS_FSCACHE
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Makes CIFS FS-Cache capable. Say Y here if you want your CIFS data
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to be cached locally on disk through the general filesystem cache
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manager. If unsure, say N.
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config CIFS_ROOT
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bool "SMB root file system (Experimental)"
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depends on CIFS=y && IP_PNP
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help
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Enables root file system support over SMB protocol.
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Most people say N here.
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@ -21,3 +21,5 @@ cifs-$(CONFIG_CIFS_DFS_UPCALL) += dns_resolve.o cifs_dfs_ref.o dfs_cache.o
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cifs-$(CONFIG_CIFS_FSCACHE) += fscache.o cache.o
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cifs-$(CONFIG_CIFS_SMB_DIRECT) += smbdirect.o
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cifs-$(CONFIG_CIFS_ROOT) += cifsroot.o
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@ -607,6 +607,7 @@ struct smb_vol {
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__u32 handle_timeout; /* persistent and durable handle timeout in ms */
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unsigned int max_credits; /* smb3 max_credits 10 < credits < 60000 */
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__u16 compression; /* compression algorithm 0xFFFF default 0=disabled */
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bool rootfs:1; /* if it's a SMB root file system */
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};
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/**
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@ -764,6 +765,7 @@ struct TCP_Server_Info {
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* reconnect.
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*/
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int nr_targets;
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bool noblockcnt; /* use non-blocking connect() */
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};
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struct cifs_credits {
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@ -0,0 +1,83 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* SMB root file system support
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*
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* Copyright (c) 2019 Paulo Alcantara <palcantara@suse.de>
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*/
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/types.h>
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#include <linux/ctype.h>
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#include <linux/string.h>
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#include <linux/root_dev.h>
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#include <linux/kernel.h>
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#include <linux/in.h>
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#include <linux/inet.h>
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#include <net/ipconfig.h>
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#define DEFAULT_MNT_OPTS \
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"vers=1.0,cifsacl,mfsymlinks,rsize=1048576,wsize=65536,uid=0,gid=0," \
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"hard,rootfs"
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static char root_dev[2048] __initdata = "";
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static char root_opts[1024] __initdata = DEFAULT_MNT_OPTS;
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static __be32 __init parse_srvaddr(char *start, char *end)
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{
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char addr[sizeof("aaa.bbb.ccc.ddd")];
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int i = 0;
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while (start < end && i < sizeof(addr) - 1) {
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if (isdigit(*start) || *start == '.')
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addr[i++] = *start;
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start++;
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}
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addr[i] = '\0';
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return in_aton(addr);
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}
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/* cifsroot=//<server-ip>/<share>[,options] */
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static int __init cifs_root_setup(char *line)
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{
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char *s;
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int len;
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__be32 srvaddr = htonl(INADDR_NONE);
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ROOT_DEV = Root_CIFS;
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if (strlen(line) > 3 && line[0] == '/' && line[1] == '/') {
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s = strchr(&line[2], '/');
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if (!s || s[1] == '\0')
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return 1;
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s = strchrnul(s, ',');
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len = s - line + 1;
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if (len <= sizeof(root_dev)) {
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strlcpy(root_dev, line, len);
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srvaddr = parse_srvaddr(&line[2], s);
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if (*s) {
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snprintf(root_opts, sizeof(root_opts), "%s,%s",
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DEFAULT_MNT_OPTS, s + 1);
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}
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}
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}
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root_server_addr = srvaddr;
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return 1;
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}
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__setup("cifsroot=", cifs_root_setup);
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int __init cifs_root_data(char **dev, char **opts)
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{
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if (!root_dev[0] || root_server_addr == htonl(INADDR_NONE)) {
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printk(KERN_ERR "Root-CIFS: no SMB server address\n");
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return -1;
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}
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*dev = root_dev;
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*opts = root_opts;
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return 0;
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}
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@ -96,7 +96,7 @@ enum {
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Opt_multiuser, Opt_sloppy, Opt_nosharesock,
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Opt_persistent, Opt_nopersistent,
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Opt_resilient, Opt_noresilient,
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Opt_domainauto, Opt_rdma, Opt_modesid,
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Opt_domainauto, Opt_rdma, Opt_modesid, Opt_rootfs,
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Opt_compress,
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/* Mount options which take numeric value */
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@ -266,6 +266,7 @@ static const match_table_t cifs_mount_option_tokens = {
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{ Opt_ignore, "nomand" },
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{ Opt_ignore, "relatime" },
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{ Opt_ignore, "_netdev" },
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{ Opt_rootfs, "rootfs" },
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{ Opt_err, NULL }
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};
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@ -1777,6 +1778,11 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
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case Opt_nodfs:
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vol->nodfs = 1;
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break;
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case Opt_rootfs:
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#ifdef CONFIG_CIFS_ROOT
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vol->rootfs = true;
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#endif
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break;
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case Opt_posixpaths:
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vol->posix_paths = 1;
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break;
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@ -2727,7 +2733,8 @@ cifs_get_tcp_session(struct smb_vol *volume_info)
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goto out_err_crypto_release;
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}
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tcp_ses->noblocksnd = volume_info->noblocksnd;
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tcp_ses->noblockcnt = volume_info->rootfs;
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tcp_ses->noblocksnd = volume_info->noblocksnd || volume_info->rootfs;
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tcp_ses->noautotune = volume_info->noautotune;
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tcp_ses->tcp_nodelay = volume_info->sockopt_tcp_nodelay;
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tcp_ses->rdma = volume_info->rdma;
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@ -3873,7 +3880,11 @@ generic_ip_connect(struct TCP_Server_Info *server)
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socket->sk->sk_sndbuf,
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socket->sk->sk_rcvbuf, socket->sk->sk_rcvtimeo);
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rc = socket->ops->connect(socket, saddr, slen, 0);
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rc = socket->ops->connect(socket, saddr, slen,
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server->noblockcnt ? O_NONBLOCK : 0);
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if (rc == -EINPROGRESS)
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rc = 0;
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if (rc < 0) {
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cifs_dbg(FYI, "Error %d connecting to server\n", rc);
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sock_release(socket);
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@ -8,6 +8,7 @@
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enum {
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Root_NFS = MKDEV(UNNAMED_MAJOR, 255),
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Root_CIFS = MKDEV(UNNAMED_MAJOR, 254),
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Root_RAM0 = MKDEV(RAMDISK_MAJOR, 0),
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Root_RAM1 = MKDEV(RAMDISK_MAJOR, 1),
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Root_FD0 = MKDEV(FLOPPY_MAJOR, 0),
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