Re: [V9fs-developer] [PATCH] Add support for 9P as a root filesystem

[Eric Van Hensbergen]

Is this still strictly necessary?  I thought the guys booting with a
root using virtfs didn't need this -- but perhaps their approach
depends on specific configurations in an initrd and this doesn't?

        -eric

(Add cc: linux-fs and cc: linux-kernel)

On Mon, May 14, 2012 at 9:29 AM, Ian Kirk <blob@xxxxxxxxxx> wrote:
> This patch adds support for running a 9P filesystem as root using a method
> similar to NFS root. Passing root=9p to the Kernel command line works
> in a comparable way to passing root=nfs
>
> Signed-off-by: Ian Kirk <blob@xxxxxxxxxx>
> ---
>  fs/9p/Kconfig            |    7 +++++++
>  include/linux/root_dev.h |    1 +
>  init/do_mounts.c         |   25 +++++++++++++++++++++++++
>  3 files changed, 33 insertions(+), 0 deletions(-)
>
> diff --git a/fs/9p/Kconfig b/fs/9p/Kconfig
> index 0a93dc1..ffd73f5 100644
> --- a/fs/9p/Kconfig
> +++ b/fs/9p/Kconfig
> @@ -31,4 +31,11 @@ config 9P_FS_POSIX_ACL
>
>          If you don't know what Access Control Lists are, say N
>
> +config ROOT_9P
> +       bool "9p root filesystem"
> +       depends on 9P_FS=m || 9P_FS=y
> +       help
> +         Permits you to pass root=9p to the kernel command line and have the
> +         root filesystem on 9p
> +
>  endif
> diff --git a/include/linux/root_dev.h b/include/linux/root_dev.h
> index ed241aa..61633ed 100644
> --- a/include/linux/root_dev.h
> +++ b/include/linux/root_dev.h
> @@ -7,6 +7,7 @@
>
>  enum {
>        Root_NFS = MKDEV(UNNAMED_MAJOR, 255),
> +       Root_9P = MKDEV(UNNAMED_MAJOR, 254),
>        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 2974c8b..4ec8dce 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -212,6 +212,9 @@ dev_t name_to_dev_t(char *name)
>        res = Root_RAM0;
>        if (strcmp(name, "ram") == 0)
>                goto done;
> +       res = Root_9P;
> +       if (strcmp(name, "9p") == 0)
> +               goto done;
>
>        if (strlen(name) > 31)
>                goto fail;
> @@ -439,6 +442,18 @@ static int __init mount_nfs_root(void)
>  }
>  #endif
>
> +#ifdef CONFIG_ROOT_9P
> +static int __init mount_9p_root(void)
> +{
> +       int err = do_mount_root("root", "9p", root_mountflags, root_mount_data);
> +
> +       if (err == 0)
> +               return 1;
> +
> +       return 0;
> +}
> +#endif
> +
>  #if defined(CONFIG_BLK_DEV_RAM) || defined(CONFIG_BLK_DEV_FD)
>  void __init change_floppy(char *fmt, ...)
>  {
> @@ -471,6 +486,16 @@ void __init change_floppy(char *fmt, ...)
>
>  void __init mount_root(void)
>  {
> +#ifdef CONFIG_ROOT_9P
> +       if (MAJOR(ROOT_DEV) == UNNAMED_MAJOR) {
> +               if (mount_9p_root())
> +                       return;
> +
> +               printk(KERN_ERR "VFS: Unable to mount root fs via 9p\n");
> +
> +               ROOT_DEV = Root_FD0;
> +       }
> +#endif
>  #ifdef CONFIG_ROOT_NFS
>        if (MAJOR(ROOT_DEV) == UNNAMED_MAJOR) {
>                if (mount_nfs_root())
> --
> 1.7.1
>
>
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