[PATCH 3/3] fs: add linux_rootarg 'root=mmcblkXpN' support

[Ahmad Fatoum]

Hello Marco,

On 06.05.21 13:22, Marco Felsch wrote:
> Since commit fa2d0aa96941 ("mmc: core: Allow setting slot index via
> device tree alias") the kernel supports stable mmc device names. Since
> the barebox mmc device names matches the one from the kernel we can pass
> the 'root=mmcblkXpN' argument on commandline to refer to the correct
> boot medium.
> 
> This patch adds the support to store the above commandline as
> linux_rootarg if enabled. Use the partuuid as fallback since it is not
> as unique as the mmcblkXpN scheme. Add a own build option since the
> system integrator needs to check if the used kernel contains the above
> commit.
> 
> Signed-off-by: Marco Felsch <m.felsch at pengutronix.de>
> ---
> Hi all,
> 
> I know that:
> 8<-----------------
> +		if (!str && fsdev->cdev->partuuid[0] != 0)
> +			str = basprintf("root=PARTUUID=%s", fsdev->cdev->partuuid);
> 8<-----------------
> is longer than 80char but for the sake of readability I kept that
> oneliner. Should we update checkpatch accordingly to match the new linux
> rule?

Yes, I already adhere to the new Linux convention in my barebox code.

> 
> Regards,
>   Marco
> 
> 
>  common/Kconfig | 15 +++++++++++++++
>  fs/fs.c        | 48 ++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 59 insertions(+), 4 deletions(-)
> 
> diff --git a/common/Kconfig b/common/Kconfig
> index 6b3c1701be..a09a1d9456 100644
> --- a/common/Kconfig
> +++ b/common/Kconfig
> @@ -700,6 +700,21 @@ config FLEXIBLE_BOOTARGS
>  	  to replace parts of the bootargs string without reconstructing it
>  	  completely.
>  
> +config MMCBLKDEV_ROOTARG
> +	bool
> +	prompt "Support 'root=mmcblkXpN' cmdline appending"
> +	help
> +	  Enable this option to append 'root=mmcblkXpN' to the kernel cmdline
> +	  instead of 'root=PARTUUID=XYZ'. Don't enale this option if your used
> +	  kernel don't contain commit [1].

Could you add the first mainline Linux release that includes the commit?

> +
> +	  The appending only happen if barebox 'linux.bootargs.bootm.appendroot'
> +	  variable is set or the used blspec entry contains 'linux-appendroot'.
> +
> +	  [1] fa2d0aa96941 ("mmc: core: Allow setting slot index via device tree
> +	      alias")
> +
> +
>  config BAREBOX_UPDATE
>  	bool "In-system barebox update infrastructure"
>  
> diff --git a/fs/fs.c b/fs/fs.c
> index 881dc2fca0..8ee1e7febe 100644
> --- a/fs/fs.c
> +++ b/fs/fs.c
> @@ -2831,6 +2831,39 @@ out:
>  }
>  EXPORT_SYMBOL(chdir);
>  
> +static char *get_linux_mmcblkdev(struct fs_device_d *fsdev)
> +{
> +	struct cdev *cdevm, *cdev;
> +	int id, partnum;
> +	bool found = false;
> +
> +	cdevm = fsdev->cdev->master;
> +	id = of_alias_get_id(cdevm->device_node, "mmc");
> +	if (id < 0)
> +		return NULL;
> +
> +	partnum = 1; /* linux partitions are 1 based */
> +	list_for_each_entry(cdev, &cdevm->partitions, partition_entry) {
> +
> +		/*
> +		 * Partname is not guaranteed but this partition cdev is listed
> +		 * in the partitions list so we need to count it instead of
> +		 * skipping it.
> +		 */
> +		if (cdev->partname &&
> +		    !strcmp(cdev->partname, fsdev->cdev->partname)) {
> +			found = true;

You can return the basprintf() here directly

> +			break;
> +		}
> +		partnum++;
> +	}
> +
> +	if (!found)
> +		return NULL;
> +
> +	return basprintf("root=/dev/mmcblk%dp%d", id, partnum);

Then you can return NULL here and drop found.

> +}
> +
>  /*
>   * Mount a device to a directory.
>   * We do this by registering a new device on which the filesystem
> @@ -2919,11 +2952,18 @@ int mount(const char *device, const char *fsname, const char *pathname,
>  
>  	fsdev->vfsmount.mnt_root = fsdev->sb.s_root;
>  
> -	if (!fsdev->linux_rootarg && fsdev->cdev && fsdev->cdev->partuuid[0] != 0) {
> -		char *str = basprintf("root=PARTUUID=%s",
> -					fsdev->cdev->partuuid);
> +	if (!fsdev->linux_rootarg && fsdev->cdev) {
> +		char *str = NULL;
> +
> +		if (IS_ENABLED(CONFIG_MMCBLKDEV_ROOTARG) &&
> +		    cdev_is_mci_dev(fsdev->cdev->master))
> +			str = get_linux_mmcblkdev(fsdev);
> +
> +		if (!str && fsdev->cdev->partuuid[0] != 0)
> +			str = basprintf("root=PARTUUID=%s", fsdev->cdev->partuuid);
>  
> -		fsdev_set_linux_rootarg(fsdev, str);
> +		if (str)
> +			fsdev_set_linux_rootarg(fsdev, str);

This assumes that barebox aliases align with those of the kernel. I think this
is at least worth a mention in the Kconfig text.

For an alternative, see f382be77f8c0 ("boot: introduce option to pass
barebox-enabled watchdog to systemd"), which parses the aliases out of the
kernel device tree without depending on the barebox ones.

Cheers,
Ahmad


>  	}
>  
>  	path_put(&path);
> 

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