[Crash-utility] [PATCH] add option -E for foreach

[Dave Anderson]

----- Original Message -----
> Hello Dave,
> 
> The patch is used to add a new option, "-E regex", to perform the
> command(s) on all commands whose names contains a match to "regex".
> "regex" is interpreted as an POSIX extended regular expression.
> 
> The new option is helpful when using to search some commands whose names
> are similar. And I think it is more reliable than "foreach <name>
> <command> | grep xxx", for information comes from command may have a
> match to "xxx".
> 
> P.S.
> The patch uses some function defined in regex.h, which is offered by glibc.

The concept is a pretty good idea.  However:

(1) It doesn't work as you've described it in the help page, and
(2) I don't like the invocation, because option characters are 
    meant to be passed to the selected command, and not for 
    consumption by the foreach command itself.

With respect to (1), your help page example shows this:

  crash> help foreach
  ... [ cut ] ...
  Display the state of tasks whose name contains a match to 'event.*':

    crash> foreach -E 'event.*' task -R state
    PID: 99     TASK: ffff8804750d5500  CPU: 0   COMMAND: "events/0"
      state = 1,

    PID: 100    TASK: ffff8804750d4ac0  CPU: 1   COMMAND: "events/1"
      state = 1,
    
    PID: 101    TASK: ffff8804750d4080  CPU: 2   COMMAND: "events/2"
      state = 1,
    ...

But your example doesn't work with the encompassing "'" characters:

  crash> foreach -E 'event.*' task -R state
  crash>

If I remove the encompassing "'" characters, it does work:
  
  crash> foreach -E event.* task -R state
  PID: 67     TASK: ffff88033833d500  CPU: 0   COMMAND: "events/0"
    state = 1, 
  
  PID: 68     TASK: ffff88033833cac0  CPU: 1   COMMAND: "events/1"
    state = 1, 
  
  PID: 69     TASK: ffff88033833c080  CPU: 2   COMMAND: "events/2"
    state = 1, 
  
  PID: 70     TASK: ffff880338367540  CPU: 3   COMMAND: "events/3"
    state = 1, 
  
  ...

So apparently regcomp() does not handle strings encompassed with
the "'" characters.

With respect to (2), however, since the process name option already 
has the "\" invocation option to prevent ambiguity with the foreach
command name:

  crash> help foreach
  ...
     name  perform the command(s) on all commands with this name.  If the
           command name can be confused with a foreach command name, then
           precede the name string with a "\".
  ... 
    
Perhaps there can be a third way of specifying the "name" option, where a
regular expression *must* be encompassed by "'" characters, and therefore:

 (a) the argument can be recognized as a POSIX expression, and
 (b) the encompassing "'" characters can be stripped off before passing the
     argument string to regcomp().

So then you could simply enter:

  crash> foreach 'event.*' task -R state

And have it described in the help page something like:

  crash> help foreach
  ...
     name  perform the command(s) on all processes with this name.  If the
           process name can be confused with a foreach command name, then
           precede the name string with a "\".  If the process name is
           enclosed within "'" characters, then the encompassed string
           is a POSIX extended regular expression that will be used to
           match process names.
  ... 

Then you can simplify things by replacing the FOREACH_E_FLAG usage with 
a FOREACH_REGEX flag that can be set in cmd_foreach() and checked 
in foreach().

Dave