[Toybox] dd man page

[Rob Landley]

On 07/12/2017 03:22 AM, Rob Landley wrote:
> Next up, a similarly close reading of the man page...

Using ubuntu 14.04 as reference:

Still dropping conv=ascii,ebcdic,ibm because that was already obsolete
30 years ago.

I can see adding conv=excl,nocreat (sure, you got notrunc already)

Adding conv=fsync but not conv=fdatasync (If this breaks somebody's
script I can add it but is "sync data but not metadata" a hair we want
to split?)

Let's see... iflag and oflag= are kind of silly. There's already
conv=excl,nocreat,excl,notrunc so why is append not there too? Why can
you have iflag=append? "direct" is micromanaging nonsense (it was
introduced for oracle's database code, we have sync if we want to be
sure it hit disk). And "directory" is just nonsensical on Linux.
(Apparently bsd can read binary directory info, but there's no _use_ for
it?)

https://lists.gnu.org/archive/html/coreutils/2014-08/msg00032.html

Sigh. But somebody did dig up a use case for nonblock:

https://stackoverflow.com/questions/32057396/how-to-flush-named-pipefifo-in-non-blocking-mode-in-busybox-shell-script

But busybox git still doesn't implement it so there can't be that big of
a demand? Hmmm...

Alright, these _might_ make sense:

  iflag=noctty,noatime,nonblock,nofollow
  oflag=append,noctty,noatime,nonblock,

These are silly:

  ?flag=direct,directory,dsync,fullblock,nocache

(If you want to drop caches for some sort of benchmark you can
echo 3 > /proc/sys/vm/drop_caches)

What on earth is count_bytes? answer: how dd should have worked in the
first place? Oh this is just a terribly designed command all around.
conv=bytes makes sense, having separate count-bytes, seek_bytes,and
skip_bytes and having them care whether you iflags= or oflags= them is
NONSENSE.

This business with sending a signal to get status? If you want dd to
output periodic progress reports (or a progress bar), DO THAT.
status=bar or status=count would have been the obvious things to do.

Ok, looking at the iflag/oflag things: noctty, noatime, nofollow, and
append don't make sense to specify for input/output. If you want it for
one you presumably want it for both. The only one that really needs to
distinguish input from output is "nonblock" (although not for the one
use case I could find, since /dev/null should never block...). And if we
needed to distinguish within conv it could just have done
conv=inonblock,ononblock.

Sigh. Nobody's requested any of this stuff yet, it's not in posix, and
even busybox hasn't bothered to implement it so far...

Right, question: should I

A) copy the existing insanity

B) just do:

  conv=append,noctty,inonblock,ononblock,nofollow,bytes
  status=bar,count

C) ignore it all and wait for people to complain about its absence?

Does anybody have strong opinions on this? I'm leaning towards door #2
myself. Posix has had 15 years to catch up on this, and declined.

Rob