Bug 834260

> Expected results:
> 
> crash> struct net_device 0xffff880312458020 | head -n 5

Ah, here the command would obviously look like:

crash> struct -o net_device 0xffff880312458020 | head -n 5

Sorry about the typo;-/

When used with an address, the struct command passes the heavy lifting
off to the embedded gdb module, and the output is straight from gdb.

When used with -o, it has gdb print the structure declaration behind the
scenes, and then walks through the output, doing an ugly parsing operation
trying to pick out strucure members, and as it finds them, queries gdb
for the member's offset, and then pushes it out before the member name.
And it's not always fully-functional, as it sometimes it "misses" some members.

Doing the same for the output of a particular structure with data would
be even uglier.  But with persistance it I suppose it could be done, 
although I'm not particularly excited about doing it.  

What would be interesting to consider as an alternative, would be to 
have "struct -o address" basically do what it does now, but instead of
printing the structure.member offset, push out the member's virtual
address -- but without the contents of the structure.  That would be
relatively easy to implement.

(In reply to comment #2)
> When used with an address, the struct command passes the heavy lifting
> off to the embedded gdb module, and the output is straight from gdb.
> 
> When used with -o, it has gdb print the structure declaration behind the
> scenes, and then walks through the output, doing an ugly parsing operation
> trying to pick out strucure members, and as it finds them, queries gdb
> for the member's offset, and then pushes it out before the member name.
> And it's not always fully-functional, as it sometimes it "misses" some
> members.
> 
> Doing the same for the output of a particular structure with data would
> be even uglier.  But with persistance it I suppose it could be done, 
> although I'm not particularly excited about doing it.

Thank you for the explanation of implementation, I was not aware there is such a difference between processing w/o the address.

> What would be interesting to consider as an alternative, would be to 
> have "struct -o address" basically do what it does now, but instead of
> printing the structure.member offset, push out the member's virtual
> address -- but without the contents of the structure.  That would be
> relatively easy to implement.

This might be actually good compromise - it's definitely better than current behavior, and it would give me what am I searching for.

> This might be actually good compromise - it's definitely better than
> current behavior, and it would give me what am I searching for.

Cool -- I like the idea as well.  I'll look into it...

Pretty straight-forward fit -- taking a thread_info struct as an
example, here's the current functionality:
  
  crash> thread_info ffff81002a796000
  struct thread_info {
    task = 0xffff81003ed767e0, 
    exec_domain = 0xffffffff802f78e0, 
    flags = 128, 
    status = 1, 
    cpu = 5, 
    preempt_count = 0, 
    addr_limit = {
      seg = 18446604435732824064
    }, 
    restart_block = {
      fn = 0xffffffff80095a52 <do_no_restart_syscall>, 
      arg0 = 0, 
      arg1 = 0, 
      arg2 = 0, 
      arg3 = 0
    }
  }
  crash> thread_info -o
  struct thread_info {
     [0] struct task_struct *task;
     [8] struct exec_domain *exec_domain;
    [16] __u32 flags;
    [20] __u32 status;
    [24] __u32 cpu;
    [28] int preempt_count;
    [32] mm_segment_t addr_limit;
    [40] struct restart_block restart_block;
  }
  SIZE: 80
  crash> thread_info -ox
  struct thread_info {
     [0x0] struct task_struct *task;
     [0x8] struct exec_domain *exec_domain;
    [0x10] __u32 flags;
    [0x14] __u32 status;
    [0x18] __u32 cpu;
    [0x1c] int preempt_count;
    [0x20] mm_segment_t addr_limit;
    [0x28] struct restart_block restart_block;
  }
  SIZE: 0x50
  crash>

And the new functionality looks like:

  crash> thread_info -o ffff81002a796000
  struct thread_info {
    [ffff81002a796000] struct task_struct *task;
    [ffff81002a796008] struct exec_domain *exec_domain;
    [ffff81002a796010] __u32 flags;
    [ffff81002a796014] __u32 status;
    [ffff81002a796018] __u32 cpu;
    [ffff81002a79601c] int preempt_count;
    [ffff81002a796020] mm_segment_t addr_limit;
    [ffff81002a796028] struct restart_block restart_block;
  }
  SIZE: 80
  crash>

Nice, thank you very much!

> And the new functionality looks like:
> 
>   crash> thread_info -o ffff81002a796000
>   struct thread_info {
>     [ffff81002a796000] struct task_struct *task;
>     [ffff81002a796008] struct exec_domain *exec_domain;
>     [ffff81002a796010] __u32 flags;
>     [ffff81002a796014] __u32 status;
>     [ffff81002a796018] __u32 cpu;
>     [ffff81002a79601c] int preempt_count;
>     [ffff81002a796020] mm_segment_t addr_limit;
>     [ffff81002a796028] struct restart_block restart_block;
>   }
>   SIZE: 80
>   crash>

(In reply to comment #6)
> Nice, thank you very much!
> 
> > And the new functionality looks like:
> > 
> >   crash> thread_info -o ffff81002a796000
> >   struct thread_info {
> >     [ffff81002a796000] struct task_struct *task;
> >     [ffff81002a796008] struct exec_domain *exec_domain;
> >     [ffff81002a796010] __u32 flags;
> >     [ffff81002a796014] __u32 status;
> >     [ffff81002a796018] __u32 cpu;
> >     [ffff81002a79601c] int preempt_count;
> >     [ffff81002a796020] mm_segment_t addr_limit;
> >     [ffff81002a796028] struct restart_block restart_block;
> >   }
> >   SIZE: 80
> >   crash>

All right -- I'll re-work the help page, and queue it up for crash-6.0.8.

Eventually it will arrive in RHEL6 presuming I can get crash onto the 
RHEL6.4 approved components list.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2013-0317.html