Re: [PATCH v2 3/6] Add fdtget utility to read property values from device tree

Hi David,

On Wed, Sep 7, 2011 at 10:25 PM, David Gibson
[off-list ref] wrote:

On Wed, Sep 07, 2011 at 12:54:17PM -0700, Simon Glass wrote:

quoted

This simply utility makes it easy for scripts to read values from the device
tree. It is written in C and uses the same libfdt as the rest of the dtc
package.

What is it for:
- Reading fdt values from scripts
- Extracting fdt information within build systems
- Looking at particular values without having to dump the entire tree

To use it, specify the fdt binary file on command line followed by a list of
node, property pairs. The utility then looks up each node, finds the property
and displays the value.

Each value is printed on a new line.

fdtget tries to guess the type of each property based on its contents. This
is not always reliable, so you can use the -t option to force fdtget to decode
the value as a string, or byte, etc.

To read from stdin, use - as the file.

Usage:
      fdtget <options> <dt file> [<node> <property>]...
Options:
      -t [<type>][<format>]   Type of data
      -h              Print this help

      <type>          One character (s=string, i=int, u=unsigned, b=byte)
      <format>        Optional format character (x=hex)

It is not terribly clear how these are combined.

A type character, then an optional format character. In fact the type
character is also optional at present since integer is assumed.

Please can you suggest a suitable help message to convey this?

Is there any way to make these more closely resemble printf() style
format specifiers?

The first patch series allowed printf specifiers but could segfault if
the user specified %s for something that was in fact not a string. I
have moved away from that as you suggested at the time. I am not keen
to re-implement printf(), or manually decode a partial subset of
printf strings, to avoid that problem. So something simple like this
is what I have come up with.

We need to encode the data size in there also - byte or integer - so
it is not quite the same as what printf is trying to do. While
printf() has %c I don't think it is a good idea to use that, since we
are printing a byte as a number, not an ASCII character.

But it is fairly close to printf, in that you can use:

-ts
-tx
-ti
-tu
-tix
-tbx

We could combine -tbx into a single letter somehow but I'm not sure I
like that idea.

I don't see any point in requiring a % since then users would expect
to be able to provide an arbitrary printf() string (see first patch
set).

So, suggestions please.

Regards,
Simon

quoted

Signed-off-by: Simon Glass <redacted>
---
Changes in v2:
- Separate arguments for node and property
- Merge two related commits into this one
- Use structure for storing display options
- Remove use of getopt_long()

 .gitignore      |    1 +
 Makefile        |    4 +
 Makefile.fdtget |   12 +++
 fdtget.c        |  200 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 217 insertions(+), 0 deletions(-)
 create mode 100644 Makefile.fdtget
 create mode 100644 fdtget.c

[snip]

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