Discovering current MTD partition

Discovering current MTD partition

[Umar Qureshey]

Hi,

I searched this list's archive but did not see anything pertinent.

I was wondering if there is a way to find out what the currently active mtd
partition is.  In my system, I have a few flash partitions for my file
system and the kernel boots with the partition that is specified on the
kernel command line.  Aside from scanning /proc/cmdline, is there a way to
programmatically ascertain which mtd partition is active *now*.  
I need to find this information within a Python script but really if it can
be done in C (perhaps a syscall?), it's all I need.

Regards,
Umar

Re: Discovering current MTD partition

[Artem Bityutskiy]

On Tue, 2011-04-26 at 16:43 -0700, Umar Qureshey wrote:
> Hi,
> 
> I searched this list's archive but did not see anything pertinent.
> 
> I was wondering if there is a way to find out what the currently active mtd
> partition is.  In my system, I have a few flash partitions for my file
> system and the kernel boots with the partition that is specified on the
> kernel command line.  Aside from scanning /proc/cmdline, is there a way to
> programmatically ascertain which mtd partition is active *now*.  
> I need to find this information within a Python script but really if it can
> be done in C (perhaps a syscall?), it's all I need.

What does active mean? Anyway, there is /proc/mtd at your disposal.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

Re: Discovering current MTD partition

[Ricard Wanderlof]

> On Wed, 27 Apr 2011, Artem Bityutskiy wrote:
> 
> > On Tue, 2011-04-26 at 16:43 -0700, Umar Qureshey wrote:
> > Hi,
> > 
> > I searched this list's archive but did not see anything pertinent.
> > 
> > I was wondering if there is a way to find out what the currently active mtd
> > partition is.  In my system, I have a few flash partitions for my file
> > system and the kernel boots with the partition that is specified on the
> > kernel command line.  Aside from scanning /proc/cmdline, is there a way to
> > programmatically ascertain which mtd partition is active *now*. 
> > I need to find this information within a Python script but really if it can
> > be done in C (perhaps a syscall?), it's all I need.
> 
> What does active mean? Anyway, there is /proc/mtd at your disposal.

If you want to find out which partition is mounted as root you could look 
at /proc/mounts .

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: Discovering current MTD partition

[umar]

> On Tue, 2011-04-26 at 16:43 -0700, Umar Qureshey wrote:
>> Hi,
>>
>> I searched this list's archive but did not see anything pertinent.
>>
>> I was wondering if there is a way to find out what the currently active
>> mtd
>> partition is.  In my system, I have a few flash partitions for my file
>> system and the kernel boots with the partition that is specified on the
>> kernel command line.  Aside from scanning /proc/cmdline, is there a way
>> to
>> programmatically ascertain which mtd partition is active *now*.
>> I need to find this information within a Python script but really if it
>> can
>> be done in C (perhaps a syscall?), it's all I need.
>
> What does active mean? Anyway, there is /proc/mtd at your disposal.
>
> --
> Best Regards,
> Artem Bityutskiy (Артём Битюцкий)
>
>
Hi,
I have multiple redundant partitions on the flash chip.  Each of these
partitions has been flashed with a file system.  The kernel resides in yet
another partition.  The bootloader loads the kernel into RAM, passes it
the kernel command line, and passes control to the kernel.  The kernel
boots and mounts the partition it was told to do so via the command line.

So, for instance, I may have this scheme:

/dev/mtd2  ---> kernel
/dev/mtd3 -----> FS #1
/dev/mtd4 -----> FS #2

The kernel can boot and mount either /dev/mtd3 or /dev/mtd4 depending on
what command line the bootloader passed to the kernel.
What I'd like is to detect from userspace is which /dev/mtdX partition is
the currently executing program running on because that is the partition
that has been obviously booted.

My fallback idea is to just bite the bullet and parse /proc/cmdline to see
which partition is being passed to the kernel.  This should work fine. 
But I was curious if there is a "cleaner" more programmatic method of
determining this information without resorting to clever regular
expressions in parsing /proc/cmdline.

Re: Discovering current MTD partition

[umar]

>
>> On Wed, 27 Apr 2011, Artem Bityutskiy wrote:
>>
>> > On Tue, 2011-04-26 at 16:43 -0700, Umar Qureshey wrote:
>> > Hi,
>> >
>> > I searched this list's archive but did not see anything pertinent.
>> >
>> > I was wondering if there is a way to find out what the currently
>> active mtd
>> > partition is.  In my system, I have a few flash partitions for my file
>> > system and the kernel boots with the partition that is specified on
>> the
>> > kernel command line.  Aside from scanning /proc/cmdline, is there a
>> way to
>> > programmatically ascertain which mtd partition is active *now*.
>> > I need to find this information within a Python script but really if
>> it can
>> > be done in C (perhaps a syscall?), it's all I need.
>>
>> What does active mean? Anyway, there is /proc/mtd at your disposal.
>
> If you want to find out which partition is mounted as root you could look
> at /proc/mounts .
>
> /Ricard

Hi,
/proc/mtd simply gives me a list of partition on the mtd device.  It
doesn't tell me which one we currently have booted from.

/proc/mounts as well doesn't relay any info about /dev/mtdXX.

~Umar

Re: Discovering current MTD partition

[umar]

> On 04/27/2011 09:25 AM, umar@janteq.com wrote:
>> Hi,
>> [...]
>> What I'd like is to detect from userspace is which /dev/mtdX partition
>> is
>> the currently executing program running on because that is the partition
>> that has been obviously booted.
>
> I think you might want to take a look at getmntent (3) : it is a libc
> function for getting the /etc/mtab entries. It also seems to be portable.
>
> Cheers,
> David.
>
> --
> David Wagner, Free Electrons
> Kernel, drivers, real-time and embedded Linux
> development, consulting, training and support.
> http://free-electrons.com

This will give me the same info as /proc/mtab.  I cannot figure out how I
can infer which /dev/mtdXX was booted from with this information.

Re: Discovering current MTD partition

[Iwo Mergler]

On Thu, 28 Apr 2011 03:14:36 umar@janteq.com wrote:
> > On 04/27/2011 09:25 AM, umar@janteq.com wrote:
> >> Hi,
> >> [...]
> >> What I'd like is to detect from userspace is which /dev/mtdX partition
> >> is
> >> the currently executing program running on because that is the partition
> >> that has been obviously booted.
> > 
> > I think you might want to take a look at getmntent (3) : it is a libc
> > function for getting the /etc/mtab entries. It also seems to be portable.
> > 
> > Cheers,
> > David.
> > 
> > --
> > David Wagner, Free Electrons
> > Kernel, drivers, real-time and embedded Linux
> > development, consulting, training and support.
> > http://free-electrons.com
> 
> This will give me the same info as /proc/mtab.  I cannot figure out how I
> can infer which /dev/mtdXX was booted from with this information.
> 

Here is an example from the embedded system I have on my desk
right now:

root:/proc# cat /proc/mounts
rootfs / rootfs rw 0 0
mtd:rfs / jffs2 rw,relatime 0 0
proc /proc proc rw,relatime 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0
etc.

From this we can see that the current root file system is
mtd:rfs

root:/proc# cat mtd
dev:    size   erasesize  name
mtd0: 00100000 00020000 "S1S2EN"
mtd1: 00400000 00020000 "rkern"
mtd2: 00b00000 00020000 "rfs"
mtd3: 00400000 00020000 "kernel"
mtd4: 02000000 00020000 "root"
etc.

This tells us that mtd:rfs corresponds to mtd2, which
should be accessible under /dev/mtd2, /dev/mtdblock2, etc.


Best regards,

Iwo



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Re: Discovering current MTD partition

[Ricard Wanderlof]

On Wed, 27 Apr 2011, umar@janteq.com wrote:

> Hi,
>
> /proc/mounts as well doesn't relay any info about /dev/mtdXX.

Sorry, you are right of course. It just seems to say /dev/root on my 
system.

The df command however seems to figure out which mtd device is mounted on 
/ . I don't know exactly how it finds this out though. I'm pretty sure it 
uses /proc/mounts, because if /proc/mounts is missing it doesn't output 
anything, but it must be getting extra information from somewhere.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: Discovering current MTD partition

[Artem Bityutskiy]

On Thu, 2011-04-28 at 09:31 +0200, Ricard Wanderlof wrote:
> On Wed, 27 Apr 2011, umar@janteq.com wrote:
> 
> > Hi,
> >
> > /proc/mounts as well doesn't relay any info about /dev/mtdXX.
> 
> Sorry, you are right of course. It just seems to say /dev/root on my 
> system.
> 
> The df command however seems to figure out which mtd device is mounted on 
> / . I don't know exactly how it finds this out though. I'm pretty sure it 
> uses /proc/mounts, because if /proc/mounts is missing it doesn't output 
> anything, but it must be getting extra information from somewhere.
> 
> /Ricard

Well, the best it to look at df sources. But here is my guess:

/dev/root must have come from the kernel command line, if I'm not
mistaken. You can find out what is your /dev/root from /proc/cmdline -
find rootfs=<xxx> there, and xxx is your device.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

Re: Discovering current MTD partition

[Ricard Wanderlof]

On Thu, 28 Apr 2011, Iwo Mergler wrote:

>> This will give me the same info as /proc/mtab.  I cannot figure out how I
>> can infer which /dev/mtdXX was booted from with this information.
>>
>
> Here is an example from the embedded system I have on my desk
> right now:
>
> root:/proc# cat /proc/mounts
> rootfs / rootfs rw 0 0
> mtd:rfs / jffs2 rw,relatime 0 0
> proc /proc proc rw,relatime 0 0
> devpts /dev/pts devpts rw,relatime,mode=600 0 0
> etc.

On the other hand, here's another example from a system on my desk:

# cat  /proc/mounts
rootfs / rootfs rw 0 0
/dev/root / jffs2 rw,relatime 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
udev /dev tmpfs rw,relatime 0 0
tmpfs /dev/shm tmpfs rw,relatime 0 0
/dev/part/rwfsblock /mnt/flash jffs2 rw,relatime 0 0
tmpfs /var tmpfs rw,relatime 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0

The root partition is just listed as /dev/root without any information 
about what that refers to. The system doesn't even have a /dev/root so 
it's just some sort of placeholder.

On the other hand, on the same system, df says:

# df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/mtdblock3           28672     22384      6288  78% /
udev                     66588         4     66584   0% /dev
tmpfs                    66588         0     66588   0% /dev/shm
/dev/part/rwfsblock     228864      5456    223408   2% /mnt/flash
tmpfs                    66588     25660     40928  39% /var

which tells exactly where the root file system is. Don't know exactly how 
it obtains the information though.

The system is running busybox so a quick look in the code for the df 
command should explain how its done.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: Discovering current MTD partition

[Ricard Wanderlof]

On Thu, 28 Apr 2011, Artem Bityutskiy wrote:

> On Thu, 2011-04-28 at 09:31 +0200, Ricard Wanderlof wrote:
>> On Wed, 27 Apr 2011, umar@janteq.com wrote:
>>
>>> Hi,
>>>
>>> /proc/mounts as well doesn't relay any info about /dev/mtdXX.
>>
>> Sorry, you are right of course. It just seems to say /dev/root on my
>> system.
>>
>> The df command however seems to figure out which mtd device is mounted on
>> / . I don't know exactly how it finds this out though. I'm pretty sure it
>> uses /proc/mounts, because if /proc/mounts is missing it doesn't output
>> anything, but it must be getting extra information from somewhere.
>>
>> /Ricard
>
> Well, the best it to look at df sources. But here is my guess:
>
> /dev/root must have come from the kernel command line, if I'm not
> mistaken. You can find out what is your /dev/root from /proc/cmdline -
> find rootfs=<xxx> there, and xxx is your device.

Well, in this case /dev/cmdline says

console=ttyS0 root=/dev/mtdblock3 rw rootfstype=jffs2 init=/linuxrc

so no mention of /dev/root there.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: Discovering current MTD partition

[Artem Bityutskiy]

On Thu, 2011-04-28 at 10:00 +0200, Ricard Wanderlof wrote:
> On Thu, 28 Apr 2011, Artem Bityutskiy wrote:
> 
> > On Thu, 2011-04-28 at 09:31 +0200, Ricard Wanderlof wrote:
> >> On Wed, 27 Apr 2011, umar@janteq.com wrote:
> >>
> >>> Hi,
> >>>
> >>> /proc/mounts as well doesn't relay any info about /dev/mtdXX.
> >>
> >> Sorry, you are right of course. It just seems to say /dev/root on my
> >> system.
> >>
> >> The df command however seems to figure out which mtd device is mounted on
> >> / . I don't know exactly how it finds this out though. I'm pretty sure it
> >> uses /proc/mounts, because if /proc/mounts is missing it doesn't output
> >> anything, but it must be getting extra information from somewhere.
> >>
> >> /Ricard
> >
> > Well, the best it to look at df sources. But here is my guess:
> >
> > /dev/root must have come from the kernel command line, if I'm not
> > mistaken. You can find out what is your /dev/root from /proc/cmdline -
> > find rootfs=<xxx> there, and xxx is your device.
> 
> Well, in this case /dev/cmdline says
> 
> console=ttyS0 root=/dev/mtdblock3 rw rootfstype=jffs2 init=/linuxrc
> 
> so no mention of /dev/root there.

/dev/root is the alias for whatever is in root=, so in your
case /dev/root = /dev/mtdblock3

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

Re: Discovering current MTD partition

[Ricard Wanderlof]

On Thu, 28 Apr 2011, Artem Bityutskiy wrote:

>> Well, in this case /dev/cmdline says
>>
>> console=ttyS0 root=/dev/mtdblock3 rw rootfstype=jffs2 init=/linuxrc
>>
>> so no mention of /dev/root there.
>
> /dev/root is the alias for whatever is in root=, so in your
> case /dev/root = /dev/mtdblock3

Yes, I understand that, I was just mentioning the fact that it was not
necessarily possible to determine the root file system partition from
/proc/mounts as it uses the /dev/root alias there.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: Discovering current MTD partition

[umar]

> On Thu, 28 Apr 2011 03:14:36 umar@janteq.com wrote:
>> > On 04/27/2011 09:25 AM, umar@janteq.com wrote:
>> >> Hi,
>> >> [...]
>> >> What I'd like is to detect from userspace is which /dev/mtdX
>> partition
>> >> is
>> >> the currently executing program running on because that is the
>> partition
>> >> that has been obviously booted.
>> >
>> > I think you might want to take a look at getmntent (3) : it is a libc
>> > function for getting the /etc/mtab entries. It also seems to be
>> portable.
>> >
>> > Cheers,
>> > David.
>> >
>> > --
>> > David Wagner, Free Electrons
>> > Kernel, drivers, real-time and embedded Linux
>> > development, consulting, training and support.
>> > http://free-electrons.com
>>
>> This will give me the same info as /proc/mtab.  I cannot figure out how
>> I
>> can infer which /dev/mtdXX was booted from with this information.
>>
>
> Here is an example from the embedded system I have on my desk
> right now:
>
> root:/proc# cat /proc/mounts
> rootfs / rootfs rw 0 0
> mtd:rfs / jffs2 rw,relatime 0 0
> proc /proc proc rw,relatime 0 0
> devpts /dev/pts devpts rw,relatime,mode=600 0 0
> etc.
>
> From this we can see that the current root file system is
> mtd:rfs
>
> root:/proc# cat mtd
> dev:    size   erasesize  name
> mtd0: 00100000 00020000 "S1S2EN"
> mtd1: 00400000 00020000 "rkern"
> mtd2: 00b00000 00020000 "rfs"
> mtd3: 00400000 00020000 "kernel"
> mtd4: 02000000 00020000 "root"
> etc.
>
> This tells us that mtd:rfs corresponds to mtd2, which
> should be accessible under /dev/mtd2, /dev/mtdblock2, etc.
>
>
> Best regards,
>
> Iwo
>
>

# cat /proc/mounts
rootfs / rootfs rw 0 0
ubi0:rootfs / ubifs rw,sync,relatime 0 0
proc /proc proc rw,relatime 0 0
tmpfs /tmp tmpfs rw,relatime 0 0
devpts /dev/pts devpts rw,relatime,gid=5,mode=620 0 0
sysfs /sys sysfs rw,relatime 0 0
debugfs /debug debugfs rw,relatime 0 0
tmpfs /webSvr/logs tmpfs rw,relatime 0 0

# cat /proc/mtd
dev:    size   erasesize  name
mtd0: 00020000 00020000 "bst"
mtd1: 00500000 00020000 "ptb"
mtd2: 00500000 00020000 "bld"
mtd3: 00500000 00020000 "hal"
mtd4: 00500000 00020000 "pba"
mtd5: 00800000 00020000 "pri"
mtd6: 00800000 00020000 "sec"
mtd7: 03c00000 00020000 "bak"
mtd8: 03c00000 00020000 "rmd"
mtd9: 03c00000 00020000 "rom"
mtd10: 00300000 00020000 "dsp"
mtd11: 03c00000 00020000 "lnx"

# df
Filesystem                Size      Used Available Use% Mounted on
ubi0:rootfs              52.7M     35.1M     17.5M  67% /
tmpfs                    65.4M     32.0K     65.4M   0% /tmp
tmpfs                    65.4M     32.0K     65.4M   0% /webSvr/logs

There's nothing above I can use to infer about which /dev/mtdXX is
currently booted - at least on this system.
I have resorted to my backup strategy of parsing /proc/cmdline within
Python to determine which partition is booted. *sigh*

Re: Discovering current MTD partition

[Artem Bityutskiy]

On Thu, 2011-04-28 at 13:26 -0400, umar@janteq.com wrote:
> # cat /proc/mounts
> rootfs / rootfs rw 0 0
> ubi0:rootfs / ubifs rw,sync,relatime 0 0
> proc /proc proc rw,relatime 0 0
> tmpfs /tmp tmpfs rw,relatime 0 0
> devpts /dev/pts devpts rw,relatime,gid=5,mode=620 0 0
> sysfs /sys sysfs rw,relatime 0 0
> debugfs /debug debugfs rw,relatime 0 0
> tmpfs /webSvr/logs tmpfs rw,relatime 0 0
> 
> # cat /proc/mtd
> dev:    size   erasesize  name
> mtd0: 00020000 00020000 "bst"
> mtd1: 00500000 00020000 "ptb"
> mtd2: 00500000 00020000 "bld"
> mtd3: 00500000 00020000 "hal"
> mtd4: 00500000 00020000 "pba"
> mtd5: 00800000 00020000 "pri"
> mtd6: 00800000 00020000 "sec"
> mtd7: 03c00000 00020000 "bak"
> mtd8: 03c00000 00020000 "rmd"
> mtd9: 03c00000 00020000 "rom"
> mtd10: 00300000 00020000 "dsp"
> mtd11: 03c00000 00020000 "lnx"
> 
> # df
> Filesystem                Size      Used Available Use% Mounted on
> ubi0:rootfs              52.7M     35.1M     17.5M  67% /
> tmpfs                    65.4M     32.0K     65.4M   0% /tmp
> tmpfs                    65.4M     32.0K     65.4M   0% /webSvr/logs
> 
> There's nothing above I can use to infer about which /dev/mtdXX is
> currently booted - at least on this system.
> I have resorted to my backup strategy of parsing /proc/cmdline within
> Python to determine which partition is booted. *sigh*

Yes, this is a bit messy and complex. Anyway, here is the algorithm for
you, in short. Ask specific questions if it is not clear, I do not have
time right now to write long mails. Anyway, you need to spend some time
and understand the relations between all these mtdX, ubiY, ubiY_Z,
ubiY:name...

So, in your case you know your rootfs is "ubi0:rootfs". This means that
   a) your rootfs is an UBI volume
   b) this UBI volume belongs to the UBI device 0 (there may be several
      of them - ubi1, ubi2, etc). This is the typical case, I do not
      know if anyone really has more than one UBI device ever.
   c) You know that the volume name is "rootfs".

You also should know that there is 1-1 correspondence between MTD and
UBI devices - one UBI device sits on top (and fully controls) one MTD
device. To find out the MTD device number you look
at: /sys/class/ubi/ubi0/mtd_num

There you see the number X, this means your MTD device is mtdX

P.S. If you had set-up similar to Ricard's, you' also need to look
at /proc/cmdline to translate "rootfs" or "/dev/rootfs" to
"ubi0:rootfs". Not, in this case it is just co-incidence that you named
your volume "rootfs", if you named it "pussy_cat", you' have the
following in your /proc/mounts:

rootfs / rootfs rw 0 0
ubi0:pussy_cat / ubifs rw,sync,relatime 0 0

HTH.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

Re: Discovering current MTD partition

[Bjørn Forsman]

On 27 April 2011 01:43, Umar Qureshey <umar@janteq.com> wrote:
> [...]
> Aside from scanning /proc/cmdline, is there a way to
> programmatically ascertain which mtd partition is active *now*.
> I need to find this information within a Python script but really if it can
> be done in C (perhaps a syscall?), it's all I need.

Busybox has a command called 'rdev' that looks up the block device
that is mounted on /.

$ busybox rdev
/dev/sda1 /

Look in busybox/util-linux/rdev.c and busybox/libbb/find_root_device.c
for the implementation details.

Best regards,
Bjørn Forsman

RE: Discovering current MTD partition

[Atlant Schmidt]

Bjørn:

> $ busybox rdev
> /dev/sda1 /

  Just FYI: This doesn't work on my particular
  Embedded Linux system (running on UBIfs).
  That command produces no result.

                        Atlant

-----Original Message-----
From: linux-mtd-bounces@lists.infradead.org [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf Of Bjørn Forsman
Sent: Thursday, April 28, 2011 14:08
To: Umar Qureshey
Cc: linux-mtd@lists.infradead.org
Subject: Re: Discovering current MTD partition

On 27 April 2011 01:43, Umar Qureshey <umar@janteq.com> wrote:
> [...]
> Aside from scanning /proc/cmdline, is there a way to
> programmatically ascertain which mtd partition is active *now*.
> I need to find this information within a Python script but really if it can
> be done in C (perhaps a syscall?), it's all I need.

Busybox has a command called 'rdev' that looks up the block device
that is mounted on /.

$ busybox rdev
/dev/sda1 /

Look in busybox/util-linux/rdev.c and busybox/libbb/find_root_device.c
for the implementation details.

Best regards,
Bjørn Forsman

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Re: Discovering current MTD partition

[umar]

> On Thu, 2011-04-28 at 13:26 -0400, umar@janteq.com wrote:
>> # cat /proc/mounts
>> rootfs / rootfs rw 0 0
>> ubi0:rootfs / ubifs rw,sync,relatime 0 0
>> proc /proc proc rw,relatime 0 0
>> tmpfs /tmp tmpfs rw,relatime 0 0
>> devpts /dev/pts devpts rw,relatime,gid=5,mode=620 0 0
>> sysfs /sys sysfs rw,relatime 0 0
>> debugfs /debug debugfs rw,relatime 0 0
>> tmpfs /webSvr/logs tmpfs rw,relatime 0 0
>>
>> # cat /proc/mtd
>> dev:    size   erasesize  name
>> mtd0: 00020000 00020000 "bst"
>> mtd1: 00500000 00020000 "ptb"
>> mtd2: 00500000 00020000 "bld"
>> mtd3: 00500000 00020000 "hal"
>> mtd4: 00500000 00020000 "pba"
>> mtd5: 00800000 00020000 "pri"
>> mtd6: 00800000 00020000 "sec"
>> mtd7: 03c00000 00020000 "bak"
>> mtd8: 03c00000 00020000 "rmd"
>> mtd9: 03c00000 00020000 "rom"
>> mtd10: 00300000 00020000 "dsp"
>> mtd11: 03c00000 00020000 "lnx"
>>
>> # df
>> Filesystem                Size      Used Available Use% Mounted on
>> ubi0:rootfs              52.7M     35.1M     17.5M  67% /
>> tmpfs                    65.4M     32.0K     65.4M   0% /tmp
>> tmpfs                    65.4M     32.0K     65.4M   0% /webSvr/logs
>>
>> There's nothing above I can use to infer about which /dev/mtdXX is
>> currently booted - at least on this system.
>> I have resorted to my backup strategy of parsing /proc/cmdline within
>> Python to determine which partition is booted. *sigh*
>
> Yes, this is a bit messy and complex. Anyway, here is the algorithm for
> you, in short. Ask specific questions if it is not clear, I do not have
> time right now to write long mails. Anyway, you need to spend some time
> and understand the relations between all these mtdX, ubiY, ubiY_Z,
> ubiY:name...
>
> So, in your case you know your rootfs is "ubi0:rootfs". This means that
>    a) your rootfs is an UBI volume
>    b) this UBI volume belongs to the UBI device 0 (there may be several
>       of them - ubi1, ubi2, etc). This is the typical case, I do not
>       know if anyone really has more than one UBI device ever.
>    c) You know that the volume name is "rootfs".
>
> You also should know that there is 1-1 correspondence between MTD and
> UBI devices - one UBI device sits on top (and fully controls) one MTD
> device. To find out the MTD device number you look
> at: /sys/class/ubi/ubi0/mtd_num
>
> There you see the number X, this means your MTD device is mtdX
>
> P.S. If you had set-up similar to Ricard's, you' also need to look
> at /proc/cmdline to translate "rootfs" or "/dev/rootfs" to
> "ubi0:rootfs". Not, in this case it is just co-incidence that you named
> your volume "rootfs", if you named it "pussy_cat", you' have the
> following in your /proc/mounts:
>
> rootfs / rootfs rw 0 0
> ubi0:pussy_cat / ubifs rw,sync,relatime 0 0
>
> HTH.
>

Yes, that definitely helps!

# cat /sys/class/ubi/ubi0/mtd_num
11

Thanks :)