[Toybox] I aten't dead.

[Isaac Dunham]

On Thu, Feb 26, 2015 at 03:19:28PM -0600, Rob Landley wrote:
> 
> 
> On 02/26/2015 12:01 PM, Isaac Dunham wrote:
> > On Thu, Feb 26, 2015 at 06:26:19AM -0600, Rob Landley wrote:
> >> On 02/25/2015 10:27 AM, Isaac Dunham wrote:
> >>> On Wed, Feb 25, 2015 at 03:19:23AM -0600, Rob Landley wrote:
> >>>> There's a marvelous book called "the unix philosophy" by mike gancarz
> >>>> that talks about output intended for humans vs output intended to be
> >>>> processed by other tools.
> >>>>
> >>>> A scriptable tool is one where you can do:
> >>>>
> >>>>   echo $(( $(wc -l < blah) * 3))
> >>>>
> >>>> If it's scriptable, the output of one tool is naturally the input to
> >>>> another. Admittedly this can be annoying to use from the command line
> >>>> such as the way "ls" with no arguments will produce no output when run
> >>>> in an empty directory. But the _reason_ for that is so "for i in $(ls);
> >>>> do blah $i; done" doesn't have to filter the ls output to use it in a
> >>>> script.
> >>>
> >>> Thread hijack/blkid feature I'd like to see (no need to do it now, I'm
> >>> willing to try writing it at a later point).
> >>>
> >>> I was just fighting with non-scriptable output in another tool:
> >>> blkid.
> >>
> >> Which is why fstype exists, although it only gives you the type not the
> >> other attributes.
> > 
> > I'm actually after just the label/just the uuid.
> 
> A properly scriptable solution would be "blkid -s label" producing
> _just_ the label output with no escapes or modifiers (which you could
> then pipe through base64 or something if you needed that).
> 
> I'm not sure whether your use case is "give me this data", "behave like
> host blkid", or whether the correct solution is to extend mdev.
> 
> >>>  -s <tag>    show specified tag(s) (default show all tags)
> >>>
> >>> <tag> is TYPE/SEC_TYPE/UUID/PARTUUID/LABEL, and means that only
> >>> the fields specified get shown, in the same order as usual.
> >>> Example:
> >>> blkid -s TYPE -s LABEL -s UUID /dev/sda1
> >>> /dev/sda1: LABEL="ECS_CDRUN" UUID="DEAD-BEEF" TYPE="vfat"
> >>
> >> If it takes a comma separated list and maybe I can get it to share code
> >> with ps -o and mount -o.
> > 
> > No, but a linked list of strings (optstring "s*") should work.
> 
> I mean if splitting fields at commas won't interfere. (You can already
> provide multiple -o to mount.)

There's no FIELD that includes commas, so I'd assume so.
 
> >>> And the ID_FS_LABEL_ENC field of -o udev matches what I'm looking for
> >>> exactly.
> >>
> >> I'm confused: what is your use case?
> > 
> > Narrowly:
> > Populate /dev/disk/by-{label,uuid}/ with symlinks having the same name 
> > that udev gives them, so that mount by label and mount by uuid work right.
> > 
> > Broadly:
> > I've been working on a package to allow busybox mdev to replace udev
> > in Debian-based distros, which has already gotten some interest from
> > others on the "Dng" list ("Dng" stands for "Debian's not Gnome"; it's
> > the list for Devuan, the fork of Debian over systemd).
> 
> Ooh, possibly I should be subscribed to that list...
> 
> > Meanwhile, Jude Nelson has been working on a daemon that should
> > be a replacement for udev (vdev); this will use helper scripts much like
> > mdev does, and I'm planning to add /dev/disk/by-label/ support for it.
> > On Debian/Devuan, I know that blkid is provided by util-linux, but
> > I'd rather be *able* to switch out components.
> 
> Being able to switch out components is a strong argument for
> compatability, and thus this insanely horrible API the blkid people put
> together without the foggiest understanding how to make something
> scriptable.
> 
> Looking at the blkdev man page: I note that the -d flag is nuts, the -c
> and -g options are also nuts (why is this the end user's problem?)...

As far as I can tell, most of blkid is nuts. It appears to be an
aggregation of features that have some tangential relationship to
"identifying block devices".

I'd just like to know that I can specify "-o value" or "-o udev"
and "-s LABEL" or "-s UUID" without getting locked into using blkid
from util-linux.

<snip>
> That said, the above appears to be the magic incantation to get LABEL
> and UUID fields. I don't have an example of one with an escaped label,
> although I point you at the tests/blkid directory if you'd like to
> submit one I can poke at.
> 
> Would implementing "-o value" and -s FIELD be sufficient for your purposes?

I think so, though if you support "-o value" it makes sense to accept
-o full (meaning "same as normal").
If it's viable, "-o udev" would be nice.

> >> In theory properly quoted shell strings shouldn't care what their
> >> contents are (modulo NUL bytes and stripping trailing whitespace):
> >>
> >>   X="$(fruitbat -x)"
> >>   command "$X"
> >>
> >> Should be fine about having semicolons and quotes and stuff in what $X
> >> expands to...? So the classic definition of "scriptable" would be not
> >> having any LABEL= at all, but instead having a way to request the
> >> specific field of interest...?
> > 
> > Which is  what "blkid -s LABEL -o value" does.
> 
> Is using that bad?

Only because neither toybox nor busybox implement it.
If either one did, I'd go ahead and use it without a second thought.

> > But any of the other 
> > 
> >> (And if you want a label that's really screwing with mount-by-label, put
> >> a / in it.)
> > 
> > udev/blkid -o udev handles this by converting all "unsafe" chars to
> > "\x<hex value>" so a label "/" becomes "/dev/disk/by-label/\x2f".
> 
> Hmmm, I remember there being a way to do that...
> 
> Not cat -v, not uuencode, not base64... grrr, I remember having done it,
> but not how. And of course with blkid -o format controls _both_ labeling
> and escaping without any orthogonal control for the specific field.
> Because they hate Don Norman.
> 
> > Thanks,
> > Isaac Dunham
> 
> Rob
Isaac Dunham

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