Storage size of isn't known

Question

This is part of an IOCTL switch case. I am getting the following error?

error: storage size of 'data' isn't known error: 'mesg' undeclared (first use in this function)

case PASS_STRUCT:

        struct mesg{
            int pIDs[SIZE];
            int niceVal;
        };

        struct mesg data;

        ret = copy_from_user(&data, arg, sizeof(data));
        if(ret < 0){
            printk("PASS_STRUCT\n");
            return -1;  
        }

        printk("Message PASS_STRUCT : %d\n",data.niceVal);
        break;

SIZE value is set before creating mesg.

cnicutar · Answer 1 · 2012-08-26T15:36:03.113

2

struct mesg{
    int pIDs[SIZE];
    int niceVal;
};
SIZE value is set before creating mesg.

In C SIZE needs to be a true compile-time constant to use it like that. Something like:

#define SIZE 10

You also should move the structure declaration outside the switch.

edited Aug 26 '12 at 15:36

answered Aug 26 '12 at 15:25

cnicutar

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the SIZE of the pIDs array changes upon each all to this driver, it is not defined as #define SIZE 10. What can be done? – user340 Aug 26 '12 at 15:40
@kani Yeah. It will bring other changes though. – cnicutar Aug 26 '12 at 15:43
Hmm yeah :-( can you have a look at this. http://stackoverflow.com/questions/12130689/passing-struct-to-device-driver-through-ioctl. I define SIZE before calling PASS_STRUCT can't any thing done in that code? – user340 Aug 26 '12 at 15:49
1

@kani Read more about `C` and Linux internals: it will be easier than just dragging the code one question to the other – cnicutar Aug 26 '12 at 15:51
Will #define SIZE 10 be able to be changed at runtime? – user340 Aug 26 '12 at 16:02
@kani No, once you define it it becomes "text". – cnicutar Aug 26 '12 at 16:03
with a the same code above, now am getting this error: expected expression before 'struct'. What do you think of this? – user340 Aug 26 '12 at 16:11
1

@kani, If you want the array size to be dynamic, then you really want an `int numIDs` element and change `pIDs` to a pointer (`int * pIDs`). Then the driver will have to allocate a memory space the size of `numIDs*sizeof(int)`, then do a `copy_from_user()` to that memory space using `pIDs`. – Joshua Aug 29 '12 at 16:33

Storage size of isn't known

1 Answers1