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Subject: Re: [PATCH] ubiblock: Support UBI volume name or volume ID
 parameter passing
From: Artem Bityutskiy <dedekind1@gmail.com>
Reply-To: dedekind1@gmail.com
To: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Date: Mon, 28 Jul 2014 19:31:11 +0300
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Cc: Richard Weinberger <richard@nod.at>, linux-mtd@lists.infradead.org,
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On Mon, 2014-07-21 at 17:53 -0300, Ezequiel Garcia wrote:
> Sorry for the delay on this one.
> 
> On 14 Apr 01:42 PM, Artem Bityutskiy wrote:
> > On Thu, 2014-04-10 at 11:43 -0300, Ezequiel Garcia wrote:
> > > +static int ubi_open_volume_by_id(libubi_t desc, const char *node, int vol_id, int mode)
> > >  {
> > > +       char file[256];
> > > +       struct ubi_dev_info dev_info;
> > >         int err, fd;
> > > -       libubi_t libubi;
> > >  
> > > -       err = parse_opt(argc, argv);
> > > +       err = ubi_get_dev_info(desc, node, &dev_info);
> > >         if (err)
> > > +               return errmsg("cannot get information about UBI device \"%s\"", node);
> > > +
> > > +       sprintf(file, "/dev/ubi%d_%d", dev_info.dev_num, vol_id);
> > 
> > Device node names may ve anything. Please, do not rely on the "/dev/ubi%
> > d_%d" naming scheme in the tool.
> > 
> > I think device node can be found out by scanning "/dev" and looking at
> > the device node major/minor numbers. This is more work of course.
> > 
> 
> Yeah, but the UBI major is allocated dynamically so we can't rely on that.
> We would have to call an ioctl on each /dev device, which seems like a bit
> heavy to me.
> 
> How about scanning out the sysfs and associate a name to the UBI device
> and volume ID?

What I meant is that you have these:

/sys/class/ubi/ubiX/dev

and these

/sys/class/ubi/ubiX/ubiX_Y/dev

containing the "major:minor" pairs.

For for any X:Y you can find major:minor. Then you scan "/dev" and find
the device nodes, if they exist. If they do not exist, you may ask the
user to create a device node with these major:minor in your error
message.


-- 
Best Regards,
Artem Bityutskiy