[Crash-utility] Problem in command net -s

[Dave Anderson]

----- Original Message -----
> 
> 
> ----- Original Message -----
> > 
> > Hi Dave
> > 
> > I found a problem with the net -s command. It concerns line 1451 in net.c
> > 
> > struct_socket = inode - SIZE(socket);
> > 
> > As I understand it we have the type
> > 
> > struct socket_alloc {
> >    struct socket socket;
> >    struct inode vfs_inode;
> > }
> > 
> > and we have the address of the second field and want the address of
> > the first. The calculation, using the size of the socket struct,
> > used in net.c require that the second field is aligned directly
> > after the first field. This is unfortunately not true in cases I
> > have seen. By changing the line 1451 to:
> >
> > struct_socket = inode - MEMBER_OFFSET("socket_alloc", "vfs_inode");
> > 
> > things work better.
> > 
> > Is this something you would like to change in Crash? I assume you
> > will move the offset calculation to somewhere else so it is only
> > performed once.
> 
> Probably so...
> 
> Although I'm curious -- what kernel version do you see this on?
> It works as expected on RHEL5, RHEL6 and a Fedora 16 3.1.7-based
> kernel.  What do you see when you do this:
> 
>   crash> socket_alloc -o
>   struct socket_alloc {
>       [0] struct socket socket;
>      [48] struct inode vfs_inode;
>   }
>   SIZE: 616
>   crash> socket
>   struct socket {
>       socket_state state;
>       short int type;
>       long unsigned int flags;
>       struct socket_wq *wq;
>       struct file *file;
>       struct sock *sk;
>       const struct proto_ops *ops;
>   }
>   SIZE: 48
>   crash>
> 
> And just for the changelog description, what havoc does it wreak?
> 
> Thanks,
>   Dave

Interesing -- I see the problem with the 3 sample ARM dumpfiles I have
on hand.  I would have thought the same issue would be seen with 
a 32-bit x86, but it looks like it's an ARM compiler issue?

Check this comparison -- while the inode structure is different in
these two kernels, the socket structure is the same:

X86:                                   ARM:

crash> socket_alloc -o                 crash> socket_alloc -o
struct socket_alloc {                  struct socket_alloc {            
    [0] struct socket socket;             [0] struct socket socket;
   [28] struct inode vfs_inode;          [32] struct inode vfs_inode;
}                                      }
SIZE: 388                              SIZE: 584
crash> socket -o                       crash> socket -o
struct socket {                        struct socket {
   [0] socket_state state;                [0] socket_state state;
   [4] short int type;                    [4] short int type;
   [8] long unsigned int flags;           [8] long unsigned int flags;
  [12] struct socket_wq *wq;             [12] struct socket_wq *wq;
  [16] struct file *file;                [16] struct file *file;
  [20] struct sock *sk;                  [20] struct sock *sk;
  [24] const struct proto_ops *ops;      [24] const struct proto_ops *ops;
}                                      }
SIZE: 28                               SIZE: 28
crash>                                 crash>

But for whatever reason, the ARM kernel pushes the vfs_inode to
offset 32 even though the preceding socket structure is 28 bytes long.

Anyway, using the offset instead of the size is a better idea, so I'll
make that change.

Although -- my sample ARM dumpfiles don't have any tasks with open sockets,
so I still am interested in seeing what the failure looks like for the
changelog entry.

Thanks,
  Dave