This program which is from
http://www.kernel.org/doc/man-pages/online/pages/man3/fopencookie.3.html
The webpage also stated that if error happens, write should return -1;

But I found that returning -1 will crash the program. The reason is
explained in this bugzilla report.
http://sourceware.org/bugzilla/show_bug.cgi?id=2074

But glibc did fix the above bug.

Linux driver will also return negative value when error happens, Does
it have the same problem as the program here?

//===========================================================
#define _GNU_SOURCE
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include "assert.h"

#define INIT_BUF_SIZE 4

struct memfile_cookie {
   char   *buf;        /* Dynamically sized buffer for data */
   size_t  allocated;  /* Size of buf */
   size_t  endpos;     /* Number of characters in buf */
   off_t   offset;     /* Current file offset in buf */
};

ssize_t
memfile_write(void *c, const char *buf, size_t size)
{
   return -1;
}

ssize_t
memfile_read(void *c, char *buf, size_t size)
{
 assert(0);
 return 0;
}

int
memfile_seek(void *c, off64_t *offset, int whence)
{
  assert(0);
  return 0;
}

int
memfile_close(void *c)
{
   struct memfile_cookie *cookie = c;

   free(cookie->buf);
   cookie->allocated = 0;
   cookie->buf = NULL;

   return 0;
}

int
main(int argc, char *argv[])
{
   cookie_io_functions_t  memfile_func = {
	   .read  = memfile_read,
	   .write = memfile_write,
	   .seek  = memfile_seek,
	   .close = memfile_close
   };
   FILE *fp;
   struct memfile_cookie mycookie;

   /* Set up the cookie before calling fopencookie() */

   mycookie.buf = malloc(INIT_BUF_SIZE);
   if (mycookie.buf == NULL) {
	   perror("malloc");
	   exit(EXIT_FAILURE);
   }

   mycookie.allocated = INIT_BUF_SIZE;
   mycookie.offset = 0;
   mycookie.endpos = 0;

   fp = fopencookie(&mycookie,"w+", memfile_func);
   if (fp == NULL) {
	   perror("fopencookie");
	   exit(EXIT_FAILURE);
   }
   
	enum CONST_T{BUFF_SIZE=9000};
	char buff[BUFF_SIZE]={"good out"};
	size_t out=fwrite(buff,BUFF_SIZE,1,fp);
	fprintf(stderr,"output size:%d\n",out);
	   
   exit(EXIT_SUCCESS);
}
//===========================================================