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

[Marco Felsch <m.felsch@pengutronix.de>]

Hi Ahmad,

On 21-05-06 14:19, Ahmad Fatoum wrote:
> 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@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?

Yep, will add it.

> > +
> > +	  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

You're right.

> > +			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.

IMHO mention it within the Kconfig should be enough, since in an ideal
world the barebox-dt should be used by kernel as well.

> 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.

That's interessint as well, but spreads the logic around. Therefore I
would keep my solution an add a note within the Kconfig. Is that OK for
you?

Regards,
  Marco

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