linux-kernel - Re: [dm-devel] [PATCH v6 0/3] dm: boot a mapped device without an initramfs

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Date:   Thu, 4 May 2017 14:20:07 +0100
From:   Alasdair G Kergon <agk@...hat.com>
To:     Enric Balletbo Serra <eballetbo@...il.com>
Cc:     Kees Cook <keescook@...omium.org>, Will Drewry <wad@...omium.org>,
        Guenter Roeck <groeck@...gle.com>,
        Mike Snitzer <snitzer@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        David Zeuthen <zeuthen@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-raid@...r.kernel.org,
        dm-devel@...hat.com,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Shaohua Li <shli@...nel.org>, Alasdair Kergon <agk@...hat.com>
Subject: Re: [dm-devel] [PATCH v6 0/3] dm: boot a mapped device without an
        initramfs

Some more thoughts with your example, dmsetup might look like:

# dmsetup create --bootformat "lroot:uuid,rw,0 2097152 linear 8:2 0, \
2097152 2097152 linear 8:3 0, 4194304 2097152 linear 8:4 0"

- also supporting creating multiple devices if the semi-colon is used

- colon to separate name from uuid, like we already do major:minor 
- colon to separate other flags from rw if we need them in future

- splitting first on a unescaped semi-colons, then on the first two
unescaped commas, and then on unescaped commas and then unescaped spaces
within the table

- backslash escapes the following character so it is never a treated
as a separator
  - lroot\:uuid\;\\\ \"\, would be a device with no uuid and the name
    lroot:uuid;\ ",  (on a non-udev system without name mangling)

# dmsetup ls --bootformat lroot
dm="lroot:uuid,rw,0 2097152 linear 8:2 0, 2097152 2097152 \
linear 8:3 0, 4194304 2097152 linear 8:4 0"

# dmsetup ls --bootformat
(all devices on one output line)

While the code also supports devices in the /dev/sda2 format for 
convenience, please use the preferred 8:2 format in any implementation
and documented examples (to avoid the unnecessary dependency on /dev and
its dependencies).

Or with some alternative name for the option
--boot[format|param]
--short[format]
--kernelparam
--condensed
other suggestions?

dmsetup create --condensed
dmsetup ls --condensed

Alasdair