Wireshark · Wireshark-dev: [Wireshark-dev] Frame Data Buffer Allocation

[Paul Offord <Paul.Offord@xxxxxxxxxxxx>]

Hi,

 

Still working on my block dissector.  All works OK if the block size is less than 2KB but not for bigger blocks.  The problem is that my registered block handler gets called with a wtapng_block that has a frame data buffer with 2KB of allocated memory.  This memory is allocated in file_access.c at this block of code:

 

success:

               wth->rec_data = (struct Buffer *)g_malloc(sizeof(struct Buffer));

               ws_buffer_init(wth->rec_data, 1500);

 

ws_buffer_init looks like this:

 

#define SMALL_BUFFER_SIZE (2 * 1024) /* Everyone still uses 1500 byte frames, right? */

static GPtrArray *small_buffers = NULL; /* Guaranteed to be at least SMALL_BUFFER_SIZE */

/* XXX - Add medium and large buffers? */

 

/* Initializes a buffer with a certain amount of allocated space */

void

ws_buffer_init(Buffer* buffer, gsize space)

{

               g_assert(buffer);

               if G_UNLIKELY(!small_buffers) small_buffers = g_ptr_array_sized_new(1024);

 

               if (space <= SMALL_BUFFER_SIZE) {

                              if (small_buffers->len > 0) {

                                             buffer->data = "" g_ptr_array_remove_index(small_buffers, small_buffers->len - 1);

                              } else {

                                             buffer->data = "">

                              }

                              buffer->allocated = SMALL_BUFFER_SIZE;

               } else {

                              buffer->data = "">

                              buffer->allocated = space;

               }

               buffer->start = 0;

               buffer->first_free = 0;

}

 

The ws_buffer_init is called specifying a space value of 1500 bytes and ws_buffer_init decides we just need a “small buffer” which is 2KB.  It’s this 2KB buffer that I get in my block handler.

 

I’m not sure what I am supposed to do at that point.  Should my block handler just free the 2KB and then g_malloc a block of a suitable size?

 

Thanks and regards…Paul

 

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