[Crash-utility] [PATCH 1/1] CLI list command, print deep structure members

[Dave Anderson]

----- Original Message -----
> On Tue, Apr 28, 2015 at 09:44:43AM -0400, Dave Anderson wrote:
> > ----- Original Message -----
> > > ----- Original Message -----
> > > > Hi Dave,
> > > > 
> > > > I found it useful to be able listing structure's fields which are
> > > > resided
> > > > deeper than the first level:
> > > > 
> > > > crash> list super_block.s_list -s
> > > > super_block.s_id,s_dquot.info[1].dqi_dirty_list,s_dquot.dqonoff_mutex.count.counter
> > > > -H 0xc0a9c800
> > > > de805c00
> > > > s_id =
> > > > "sysfs\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> > > > s_dquot.info[1].dqi_dirty_list = {
> > > >   next = 0x0,
> > > >   prev = 0x0
> > > > },
> > > > s_dquot.dqonoff_mutex.count.counter = 1
> > > > de805800
> > > > s_id =
> > > > "rootfs\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> > > > s_dquot.info[1].dqi_dirty_list = {
> > > >   next = 0x0,
> > > >   prev = 0x0
> > > > },
> > > > s_dquot.dqonoff_mutex.count.counter = 1
> > > > 
> > > > Here is a draft patch which contains corresponding logic.
> > > > I will appreciate your comments and suggestions.
> > > > 
> > > > Best regards,
> > > > Alexandr
> > > 
> > > Hi Alexandr,
> > > 
> > > This looks quite useful.
> > > 
> > > I haven't looked at the details, but this kind of change modifies an a critical
> > > area of usage that I cannot risk breaking.
> > > 
> > > To prevent any kind of possible regression/breakage or other unexpected behavior,
> > > would it be possible to call parse_for_member_new() *only* if it is required?
> > > In other words, if the commented-out MEMBER_EXISTS() call fails, then you could
> > > set a flag to force it to attempt parse_for_member_new().  Otherwise, it could
> > > continue to use the older/simpler parse_for_member() function.
> 
> Sounds reasonable. Will do.
> 
> > > I'll dig into the patch later, test it out, etc., and it's entirely possible
> > > that I'll change my mind, but paranoia forces me to err on the side of
> > > caution.
> > > 
> > > Dave
> >  
> > Another issue that comes to mind is that there are several other instances
> > in the crash utility command set besides the "list" command that specify
> > arguments that can be expressed in the "struct.member" format.
> > 
> > By any chance, did you also attempt to fit this capability into the "struct"
> > command itself?  And then there's also "tree", "task -R", "waitq", etc.
> 
> Haven't seen these commands before, will check.
> However I've found some issue while testing, so please wait with review
> until I send fixed version.

OK good -- apparently my paranoia was legitimate!  ;-)

Anyway, if this feature can be shoe-horned into the basic "struct" command,
then making it work for all of the other lesser-used commands should be trivial.

But please keep the original parse_for_member() command available for use by
the simple "struct.member" cases.

Thanks,
  Dave