This introduces a new kernel command-line option called 'v9fsroot='
which will tell the kernel to mount the root file system by
utilizing the 9p protocol.
This allows us to mount host folder as rootfs for guest linux in qemu.
Bellow is an example which mounts v9fs with tag 'r' as rootfs in qemu
guest via virtio transport.
$ qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \
-virtfs local,path=$rootfs_dir,mount_tag=r,security_model=passthrough,id=r \
-kernel /path/to/linux/arch/x86/boot/bzImage -nographic \
-append "root=/dev/v9fs v9fsroot=r,trans=virtio rw console=ttyS0 3"
Signed-off-by: Changbin Du <[email protected]>
---
v2:
o use pr_err instead of printk.
o ROOT_DEV is only set after checking.
o cleanup DEFAULT_MNT_OPTS.
o do not retry mount for fd and virtio transport.
---
MAINTAINERS | 5 ++++
fs/9p/Kconfig | 6 ++++
fs/9p/Makefile | 1 +
fs/9p/v9fsroot.c | 64 ++++++++++++++++++++++++++++++++++++++++
include/linux/root_dev.h | 1 +
init/do_mounts.c | 55 ++++++++++++++++++++++++++++++++++
6 files changed, 132 insertions(+)
create mode 100644 fs/9p/v9fsroot.c
diff --git a/MAINTAINERS b/MAINTAINERS
index b706dd20ff2b..35b2c8f614d0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -239,6 +239,11 @@ F: include/trace/events/9p.h
F: include/uapi/linux/virtio_9p.h
F: net/9p/
+9P FILE SYSTEM ROOTFS SUPPORT
+R: Changbin Du <[email protected]>
+S: Supported
+F: fs/9p/v9fsroot.c
+
A8293 MEDIA DRIVER
M: Antti Palosaari <[email protected]>
L: [email protected]
diff --git a/fs/9p/Kconfig b/fs/9p/Kconfig
index 09fd4a185fd2..71c5a49f9a27 100644
--- a/fs/9p/Kconfig
+++ b/fs/9p/Kconfig
@@ -42,3 +42,9 @@ config 9P_FS_SECURITY
If you are not using a security module that requires using
extended attributes for file security labels, say N.
+
+config 9P_FS_ROOT
+ bool "9p root file system"
+ depends on 9P_FS=y
+ help
+ Enables root file system support over 9p protocol.
diff --git a/fs/9p/Makefile b/fs/9p/Makefile
index e7800a5c7395..bc2a4ef10049 100644
--- a/fs/9p/Makefile
+++ b/fs/9p/Makefile
@@ -15,3 +15,4 @@ obj-$(CONFIG_9P_FS) := 9p.o
9p-$(CONFIG_9P_FSCACHE) += cache.o
9p-$(CONFIG_9P_FS_POSIX_ACL) += acl.o
+9p-$(CONFIG_9P_FS_ROOT) += v9fsroot.o
diff --git a/fs/9p/v9fsroot.c b/fs/9p/v9fsroot.c
new file mode 100644
index 000000000000..6c9f7e335c1a
--- /dev/null
+++ b/fs/9p/v9fsroot.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 9p root file system support
+ *
+ * Copyright (c) 2021 Changbin Du <[email protected]>
+ */
+#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>
+
+static char root_dev[2048] __initdata = "";
+static char root_opts[1024] __initdata = "";
+
+/* v9fsroot=<path>[,options] */
+static int __init v9fs_root_setup(char *line)
+{
+ char *s;
+ int len;
+
+ if (strlen(line) >= 1) {
+ /* make s point to ',' or '\0' at end of line */
+ s = strchrnul(line, ',');
+ /* len is strlen(unc) + '\0' */
+ len = s - line + 1;
+ if (len > sizeof(root_dev)) {
+ pr_err("Root-V9FS: path too long\n");
+ return 1;
+ }
+ strscpy(root_dev, line, len);
+
+ if (*s) {
+ int n = snprintf(root_opts,
+ sizeof(root_opts), "%s",
+ s + 1);
+ if (n >= sizeof(root_opts)) {
+ pr_err("Root-V9FS: mount options string too long\n");
+ root_opts[sizeof(root_opts)-1] = '\0';
+ return 1;
+ }
+ }
+ }
+
+ ROOT_DEV = Root_V9FS;
+ return 1;
+}
+
+__setup("v9fsroot=", v9fs_root_setup);
+
+int __init v9fs_root_data(char **dev, char **opts)
+{
+ if (!root_dev[0]) {
+ pr_err("Root-V9FS: no rootdev specified\n");
+ return -1;
+ }
+
+ *dev = root_dev;
+ *opts = root_opts;
+
+ return 0;
+}
diff --git a/include/linux/root_dev.h b/include/linux/root_dev.h
index 4e78651371ba..becd0ee2ff87 100644
--- a/include/linux/root_dev.h
+++ b/include/linux/root_dev.h
@@ -9,6 +9,7 @@
enum {
Root_NFS = MKDEV(UNNAMED_MAJOR, 255),
Root_CIFS = MKDEV(UNNAMED_MAJOR, 254),
+ Root_V9FS = MKDEV(UNNAMED_MAJOR, 253),
Root_RAM0 = MKDEV(RAMDISK_MAJOR, 0),
Root_RAM1 = MKDEV(RAMDISK_MAJOR, 1),
Root_FD0 = MKDEV(FLOPPY_MAJOR, 0),
diff --git a/init/do_mounts.c b/init/do_mounts.c
index a78e44ee6adb..952e91f6efcb 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -287,6 +287,8 @@ dev_t name_to_dev_t(const char *name)
return Root_NFS;
if (strcmp(name, "/dev/cifs") == 0)
return Root_CIFS;
+ if (strcmp(name, "/dev/v9fs") == 0)
+ return Root_V9FS;
if (strcmp(name, "/dev/ram") == 0)
return Root_RAM0;
#ifdef CONFIG_BLOCK
@@ -536,6 +538,52 @@ static int __init mount_cifs_root(void)
}
#endif
+#ifdef CONFIG_9P_FS_ROOT
+
+extern int v9fs_root_data(char **dev, char **opts);
+
+#define V9FSROOT_TIMEOUT_MIN 5
+#define V9FSROOT_TIMEOUT_MAX 30
+#define V9FSROOT_RETRY_MAX 5
+
+static bool v9fs_should_retry(char *mount_opts)
+{
+ if (strstr(mount_opts, "trans=virtio") || strstr(mount_opts, "trans=fd"))
+ return false;
+ return true;
+}
+
+static int __init mount_v9fs_root(void)
+{
+ char *root_dev, *root_data;
+ unsigned int timeout = V9FSROOT_TIMEOUT_MIN;
+ bool should_retry;
+ int try, err;
+
+ err = v9fs_root_data(&root_dev, &root_data);
+ if (err != 0)
+ return 0;
+
+ should_retry = v9fs_should_retry(root_data);
+ for (try = 1; ; try++) {
+ err = do_mount_root(root_dev, "9p",
+ root_mountflags, root_data);
+ if (err == 0)
+ return 1;
+
+ if (!should_retry || try > V9FSROOT_RETRY_MAX)
+ break;
+
+ /* Wait, in case the server refused us immediately */
+ ssleep(timeout);
+ timeout <<= 1;
+ if (timeout > V9FSROOT_TIMEOUT_MAX)
+ timeout = V9FSROOT_TIMEOUT_MAX;
+ }
+ return 0;
+}
+#endif
+
void __init mount_root(void)
{
#ifdef CONFIG_ROOT_NFS
@@ -552,6 +600,13 @@ void __init mount_root(void)
return;
}
#endif
+#ifdef CONFIG_9P_FS_ROOT
+ if (ROOT_DEV == Root_V9FS) {
+ if (!mount_v9fs_root())
+ pr_err("VFS: Unable to mount root fs via 9p.\n");
+ return;
+ }
+#endif
#ifdef CONFIG_BLOCK
{
int err = create_dev("/dev/root", ROOT_DEV);
--
2.30.2
Hi Changbin,
I love your patch! Perhaps something to improve:
[auto build test WARNING on lwn/docs-next]
[also build test WARNING on linus/master v5.13-rc5 next-20210604]
[cannot apply to v9fs/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]
url: https://github.com/0day-ci/linux/commits/Changbin-Du/9p-add-support-for-root-file-systems/20210607-071229
base: git://git.lwn.net/linux-2.6 docs-next
config: arm-allyesconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/0day-ci/linux/commit/96098f751038703cc0fda4f018236d240a86930d
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Changbin-Du/9p-add-support-for-root-file-systems/20210607-071229
git checkout 96098f751038703cc0fda4f018236d240a86930d
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <[email protected]>
All warnings (new ones prefixed by >>):
>> fs/9p/v9fsroot.c:53:12: warning: no previous prototype for 'v9fs_root_data' [-Wmissing-prototypes]
53 | int __init v9fs_root_data(char **dev, char **opts)
| ^~~~~~~~~~~~~~
vim +/v9fs_root_data +53 fs/9p/v9fsroot.c
52
> 53 int __init v9fs_root_data(char **dev, char **opts)
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/[email protected]
On Mon, Jun 07, 2021 at 09:06:54AM +0800, kernel test robot wrote:
> Hi Changbin,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on lwn/docs-next]
> [also build test WARNING on linus/master v5.13-rc5 next-20210604]
> [cannot apply to v9fs/for-next]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
>
> url: https://github.com/0day-ci/linux/commits/Changbin-Du/9p-add-support-for-root-file-systems/20210607-071229
> base: git://git.lwn.net/linux-2.6 docs-next
> config: arm-allyesconfig (attached as .config)
> compiler: arm-linux-gnueabi-gcc (GCC) 9.3.0
> reproduce (this is a W=1 build):
> wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> chmod +x ~/bin/make.cross
> # https://github.com/0day-ci/linux/commit/96098f751038703cc0fda4f018236d240a86930d
> git remote add linux-review https://github.com/0day-ci/linux
> git fetch --no-tags linux-review Changbin-Du/9p-add-support-for-root-file-systems/20210607-071229
> git checkout 96098f751038703cc0fda4f018236d240a86930d
> # save the attached .config to linux build tree
> COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <[email protected]>
>
> All warnings (new ones prefixed by >>):
>
> >> fs/9p/v9fsroot.c:53:12: warning: no previous prototype for 'v9fs_root_data' [-Wmissing-prototypes]
> 53 | int __init v9fs_root_data(char **dev, char **opts)
> | ^~~~~~~~~~~~~~
>
This just follows the existing rootfs support manner. This function doesn't have
a dedicated header file to place. So I think we can ignore this warning.
>
> vim +/v9fs_root_data +53 fs/9p/v9fsroot.c
>
> 52
> > 53 int __init v9fs_root_data(char **dev, char **opts)
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/[email protected]
--
Cheers,
Changbin Du