[PATCH] xload: be more flexible when searching for second stage bootloader.

[Sascha Hauer]

On Wed, Sep 30, 2015 at 06:49:11PM +0100, vj wrote:
> On Wed, Sep 30, 2015 at 8:19 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> > On Tue, Sep 29, 2015 at 08:06:35PM +0100, vj wrote:
> >> On Tue, Sep 29, 2015 at 8:05 AM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> >> > On Sun, Sep 27, 2015 at 03:08:51PM +0100, Vicente Bergas wrote:
> >> >> A first stage bootloader can read fat and ext4 filesystems, and
> >> >> even both can be compiled-in at the same time.
> >> >> But then xload has a hardcoded fat filesystem mount option which
> >> >> renders ext4 unusable.
> >> >> This patch tries to mount it as ext4 if the fat attempt fails.
> >> >>
> >> >> Then, a typical use case of an ext4 formatted filesystem
> >> >> is it to be a standard linux filesystem, which contains
> >> >> boot-related files in /boot. So, when searching for the second stage
> >> >> bootloader, try /boot/barebox.bin after not finding it in /barebox.bin
> >> >>
> >> >> Signed-off-by: Vicente Bergas <vicencb at gmail.com>
> >> >> ---
> >> >>  arch/arm/mach-omap/xload.c | 4 ++++
> >> >>  1 file changed, 4 insertions(+)
> >> >>
> >> >> diff --git a/arch/arm/mach-omap/xload.c b/arch/arm/mach-omap/xload.c
> >> >> index ebcbcbc..c5e29f8 100644
> >> >> --- a/arch/arm/mach-omap/xload.c
> >> >> +++ b/arch/arm/mach-omap/xload.c
> >> >> @@ -118,6 +118,8 @@ static void *omap_xload_boot_mmc(void)
> >> >>       partname = asprintf("%s.0", diskdev);
> >> >>
> >> >>       ret = mount(partname, "fat", "/", NULL);
> >> >> +     if (ret)
> >> >> +             ret = mount(partname, "ext4", "/", NULL);
> >> >
> >> > It should also be possible to pass NULL as fs type in which case we
> >> > automatically detect the fs type. Could you check that?
> >>
> >> I didn't know that. This way it would be nicer and cleaner!
> >> So it has been tested but it didn't work :(
> >> mount calls detect_fs, detect_fs calls file_name_detect_type and
> >> file_name_detect_type calls open.
> >> open fails to open the "mmc0.0" file name
> >
> > Ok, I see. This indeed can't work as it depends on devfs being mounted
> > on /dev/. For this to work we would need a cdev_detect_filetype(const
> > char *name) which uses the cdev_* operations to read a buffer and pass
> > that to file_detect_type(). You're invited to implement that ;)
> >
> >> So, the first 128KB block can hold an MBR plus partition table, then a
> >> raw image of the MLO file can be present at offset 128KB followed by
> >> the disk partitions.
> >>
> >> In section 26.1.7.5.3 page 4939 figure 26-17 MMC/SD Booting
> >> states that raw mode detection is performed before searching for the
> >> MLO file in a filesystem.
> >>
> >> All in all, it is possible to have a "fat-free" SD-card.
> >
> > Now that you say it I remember having read about this before.
> >
> > Does this work well with the rest of barebox? In omap_env_init() we
> > mount the first mmc partition to /boot and put the environment to
> > /boot/barebox.env. That doesn't work when the first partition doesn't
> > contain a FAT. Do you put your environment somewhere else?
> 
> I was not using the environment save/restore feature and was unaware
> that it was broken.
> The environment retrieval could be improved in a similar way: try
> mounting all supported filesystems and search in "mountpoint/" and
> "mountpoint/boot/"
> But the environment save feature can't be easily supported on ext4
> because the driver does not support writes.
> Still I think that this patch is an improvement, is not the patch
> itself that broke the env save/restore, it was a new use case enabled
> by it.

Indeed. Could you create that cdev_detect_filetype() we talked about,
then this patch is good to go.

Sascha


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