[CRIU] [PATCH 1/9] parasite: Make parasite arguments variable size

[Douglas, William]

On Fri, Mar 1, 2013 at 10:05 AM, Pavel Emelyanov <xemul at parallels.com> wrote:
> On 03/01/2013 09:31 PM, Douglas, William wrote:
>> On Fri, Mar 1, 2013 at 8:02 AM, Pavel Emelyanov <xemul at parallels.com> wrote:
>>> Sometimes we don't know the exact amount of data we would want
>>> to send to parasite via args area (e.g. -- while draining fds).
>>>
>>> Fix this, by moving the args area behind the parasite blob and
>>> mmap-ing it with the run-time calculated size.
>>>
>>> Signed-off-by: Pavel Emelyanov <xemul at parallels.com>
>>>
>>> ---
>>>  arch/arm/parasite-head.S   |  2 --
>>>  arch/x86/parasite-head.S   |  3 ---
>>>  include/parasite-syscall.h |  1 +
>>>  include/parasite.h         |  2 +-
>>>  parasite-syscall.c         | 12 +++++++++---
>>>  pie/gen-offsets.sh         |  2 +-
>>>  pie/pie.lds.S.in           |  2 ++
>>>  7 files changed, 14 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/arch/arm/parasite-head.S b/arch/arm/parasite-head.S
>>> index b4bffe6..74fd4cb 100644
>>> --- a/arch/arm/parasite-head.S
>>> +++ b/arch/arm/parasite-head.S
>>> @@ -13,8 +13,6 @@ ENTRY(__export_parasite_head_start)
>>>  __export_parasite_cmd:
>>>         .long 0
>>>  __export_parasite_args:
>>> -       .long 0
>>> -       .space PARASITE_ARG_SIZE,0
>>>         .space PARASITE_STACK_SIZE,0
>>>
>>>          .space 228, 0
>>> diff --git a/arch/x86/parasite-head.S b/arch/x86/parasite-head.S
>>> index 289672c..0b62750 100644
>>> --- a/arch/x86/parasite-head.S
>>> +++ b/arch/x86/parasite-head.S
>>> @@ -15,9 +15,6 @@ ENTRY(__export_parasite_head_start)
>>>         .align 8
>>>  __export_parasite_cmd:
>>>         .long 0
>>> -__export_parasite_args:
>>> -       .long 0
>>> -       .space PARASITE_ARG_SIZE,0
>>>         .space PARASITE_STACK_SIZE,0
>>>  __export_parasite_stack:
>>>         .long 0
>>> diff --git a/include/parasite-syscall.h b/include/parasite-syscall.h
>>> index 2f32d03..ee5743e 100644
>>> --- a/include/parasite-syscall.h
>>> +++ b/include/parasite-syscall.h
>>> @@ -19,6 +19,7 @@ struct parasite_ctl {
>>>
>>>         unsigned int            *addr_cmd;                              /* addr for command */
>>>         void                    *addr_args;                             /* address for arguments */
>>> +       unsigned long           args_size;
>>>         int                     tsock;                                  /* transport socket for transfering fds */
>>>  };
>>>
>>> diff --git a/include/parasite.h b/include/parasite.h
>>> index 5d5b8df..66a559e 100644
>>> --- a/include/parasite.h
>>> +++ b/include/parasite.h
>>> @@ -2,7 +2,7 @@
>>>  #define __CR_PARASITE_H__
>>>
>>>  #define PARASITE_STACK_SIZE    (16 << 10)
>>> -#define PARASITE_ARG_SIZE      8196
>>> +#define PARASITE_ARG_SIZE_MIN  ( 1 << 13)
>>>
>>>  #define PARASITE_MAX_SIZE      (64 << 10)
>>>
>>> diff --git a/parasite-syscall.c b/parasite-syscall.c
>>> index 6cc6283..03b5546 100644
>>> --- a/parasite-syscall.c
>>> +++ b/parasite-syscall.c
>>> @@ -184,12 +184,12 @@ err:
>>>
>>>  static void *parasite_args_s(struct parasite_ctl *ctl, int args_size)
>>>  {
>>> -       BUG_ON(args_size > PARASITE_ARG_SIZE);
>>> +       BUG_ON(args_size > ctl->args_size);
>>>         return ctl->addr_args;
>>>  }
>>>
>>>  #define parasite_args(ctl, type) ({                            \
>>> -               BUILD_BUG_ON(sizeof(type) > PARASITE_ARG_SIZE); \
>>> +               BUILD_BUG_ON(sizeof(type) > PARASITE_ARG_SIZE_MIN);\
>>
>> This check makes me wonder if MIN is the correct description here.
>> Isn't this a MAX check instead?
>
> What I mean here is -- the size of the args area should be _not_ _less_
> than the size of an object we're about to put there. And since the area
> is _at_ _least_ ARG_SIZE_MIN butes, presumably this BUG_ON is correct.
>


Ah yes, thanks for the explanation.