Import code for article1, 2, 3, 4

10 files changed, 1396 insertions, 0 deletions

diff --git a/sos-code-article4/sos/assert.h b/sos-code-article4/sos/assert.h
new file mode 100644
index 0000000..a14ca0b
--- /dev/null
+++ b/sos-code-article4/sos/assert.h
@@ -0,0 +1,42 @@
+/* Copyright (C) 2004  The KOS Team
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#ifndef _SOS_ASSERT_H_
+#define _SOS_ASSERT_H_
+
+#include <drivers/bochs.h>
+#include <drivers/x86_videomem.h>
+
+/**
+ * If the expr is FALSE, print a message and halt the machine
+ */
+#define SOS_ASSERT_FATAL(expr) \
+   ({ \
+     int __res=(int)(expr); \
+     if (! __res) { \
+       asm("cli\n"); /* disable interrupts -- x86 only */ \
+       sos_bochs_printf("%s@%s:%d Assertion " # expr " failed\n", \
+			__PRETTY_FUNCTION__, __FILE__, __LINE__); \
+       sos_x86_videomem_printf(24, 0, 12, \
+                               "%s@%s:%d Assertion " # expr " failed", \
+			       __PRETTY_FUNCTION__, __FILE__, __LINE__); \
+       for (;;) asm("hlt;") ; /* Infinite loop, ie simple system halt */ \
+     } \
+   })
+
+
+#endif /* _SOS_ASSERT_H_ */
diff --git a/sos-code-article4/sos/errno.h b/sos-code-article4/sos/errno.h
new file mode 100644
index 0000000..2c7bada
--- /dev/null
+++ b/sos-code-article4/sos/errno.h
@@ -0,0 +1,40 @@
+/* Copyright (C) 2004  The SOS Team
+   Copyright (C) 1999  Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#ifndef _SOS_ERRNO_H_
+#define _SOS_ERRNO_H_
+
+/**
+ * @file errno.h
+ *
+ * SOS return value codes and errors.
+ */
+
+/* Positive values of the error codes */
+#define SOS_OK     0   /* No error */
+#define SOS_EINVAL 1   /* Invalid argument */
+#define SOS_ENOSUP 2   /* Operation not supported */
+#define SOS_ENOMEM 3   /* No available memory */
+#define SOS_EFATAL 255 /* Internal fatal error */
+
+/* A negative value means that an error occured.  For
+ *  example -SOS_EINVAL means that the error was "invalid
+ * argument" */
+typedef int sos_ret_t;
+
+#endif /* _SOS_ERRNO_H_ */
diff --git a/sos-code-article4/sos/klibc.c b/sos-code-article4/sos/klibc.c
new file mode 100644
index 0000000..277a15c
--- /dev/null
+++ b/sos-code-article4/sos/klibc.c
@@ -0,0 +1,271 @@
+/* Copyright (C) 2004  David Decotigny (with INSA Rennes for vsnprintf)
+   Copyright (C) 2003  The KOS Team
+   Copyright (C) 1999  Free Software Foundation
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#include "klibc.h"
+
+/* For an optimized version, see BSD sources ;) */
+void *memcpy(void *dst0, const void *src0, register unsigned int size)
+{
+  char *dst;
+  const char *src;
+  for (dst = (char*)dst0, src = (const char*)src0 ;
+       size > 0 ;
+       dst++, src++, size--)
+    *dst = *src;
+  return dst0;
+}
+
+/* ditto */
+void *memset(void *dst0, register int c, register unsigned int length)
+{
+  char *dst;
+  for (dst = (char*) dst0 ;
+       length > 0 ;
+       dst++, length --)
+    *dst = (char)c;
+  return dst0;
+}
+
+int memcmp(const void *s1, const void *s2, sos_size_t len)
+{
+  const unsigned char *c1, *c2;
+  unsigned int i;
+ 
+  for (i = 0, c1 = s1, c2 = s2; i < len; i++, c1++, c2++)
+    {
+      if(*c1 != *c2)
+        return *c1 - *c2;
+    }
+ 
+  return 0;
+}
+
+
+unsigned int strlen(register const char *str)
+{
+  unsigned int retval = 0;
+  
+  while (*str++)
+    retval++;
+  
+  return retval;
+}
+
+
+unsigned int strnlen(const char * s, sos_size_t count)
+{
+  const char *sc;
+  
+  for (sc = s; count-- && *sc != '\0'; ++sc)
+    /* nothing */continue;
+
+  return sc - s;
+}
+
+
+char *strzcpy(register char *dst, register const char *src, register int len)
+{
+  int i;
+
+  if (len <= 0)
+    return dst;
+  
+  for (i = 0; i < len; i++)
+    {
+      dst[i] = src[i];
+      if(src[i] == '\0')
+        return dst;
+    }
+  
+  dst[len-1] = '\0'; 
+  return dst;
+}
+
+
+char *strzcat (char *dest, const char *src, sos_size_t n)
+{
+  char *res = dest;
+  
+  for ( ; *dest ; dest++);
+  
+  for ( ; *src ; src++, dest++) {
+    *dest = *src;
+    n--;
+    if (n <= 0)
+      break;
+  }
+
+  *dest = '\0';
+  return res;
+}
+
+int strcmp(register const char *s1, register const char *s2)
+{
+  while (*s1 == *s2++)
+    if (*s1++ == 0)
+      return (0);
+  
+  return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1));
+}
+
+
+int strncmp(register const char *s1, register const char *s2, register int len)
+{
+  char c1 = '\0', c2 = '\0';
+  
+  while (len > 0)
+    {
+      c1 = (unsigned char) *s1++;
+      c2 = (unsigned char) *s2++;
+      if (c1 == '\0' || c1 != c2)
+        return c1 - c2;
+      len--;
+    }
+  
+  return c1 - c2;
+}
+
+
+/* I (d2) borrowed and rewrote this for Nachos/INSA Rennes. Thanks to
+   them for having kindly allowed me to do so. */
+int vsnprintf(char *buff, sos_size_t len, const char * format, va_list ap)
+{
+  sos_size_t i, result;
+  
+  if (!buff || !format || (len < 0))
+    return -1;
+  
+#define PUTCHAR(thechar) \
+  do { \
+    if (result < len-1) \
+      *buff++ = (thechar);  \
+    result++; \
+  } while (0)
+  
+  result = 0;
+  for(i=0 ; format[i] != '\0' ; i++){
+    switch (format[i])
+      {
+      case '%':
+	i++;
+	switch(format[i])
+	  {
+	  case '%':
+	    {
+	      PUTCHAR('%');
+	      break;
+	    }
+	  case 'i':;
+	  case 'd':
+	    {
+	      int integer = va_arg(ap,int);
+	      int cpt2 = 0;
+	      char buff_int[16];
+	      
+	      if (integer<0)
+		PUTCHAR('-');
+	      /* Ne fait pas integer = -integer ici parce que INT_MIN
+		 n'a pas d'equivalent positif (int = [-2^31, 2^31-1]) */
+	      
+	      do {
+		int m10 = integer%10;
+		m10 = (m10 < 0)? -m10:m10;
+		buff_int[cpt2++]=(char)('0'+ m10);
+		integer=integer/10;
+	      } while(integer!=0);
+	      
+	      for(cpt2 = cpt2 - 1 ; cpt2 >= 0 ; cpt2--)
+		PUTCHAR(buff_int[cpt2]);
+	      
+	      break;
+	    }
+	    
+	  case 'c':
+	    {
+	      int value = va_arg(ap,int);
+	      PUTCHAR((char)value);
+	      break;
+	    }
+	    
+	  case 's':
+	    {
+	      char *string = va_arg(ap,char *);
+	      if (! string)
+		string = "(null)";
+	      for( ; *string != '\0' ; string++)
+		PUTCHAR(*string);
+	      break;
+	    }
+
+	  case 'x':
+	    {
+	      unsigned int hexa = va_arg(ap,int);
+	      unsigned int nb;
+	      int i, had_nonzero = 0;
+	      for(i=0 ; i < 8 ; i++)
+		{
+		  nb = (unsigned int)(hexa << (i*4));
+		  nb = (nb >> 28) & 0xf;
+		  // Skip the leading zeros
+		  if (nb == 0)
+		    {
+		      if (had_nonzero)
+			PUTCHAR('0');
+		    }
+		  else
+		    {
+		      had_nonzero = 1;
+		      if (nb < 10)
+			PUTCHAR('0'+nb);
+		      else
+			PUTCHAR('a'+(nb-10));
+		    }
+		}
+	      if (! had_nonzero)
+		PUTCHAR('0');
+	      break;
+	    }
+	    break;
+	
+	  default:
+            PUTCHAR('%');
+	    PUTCHAR(format[i]);
+	  }
+	break;
+	
+      default:
+        PUTCHAR(format[i]);
+      }
+  }
+  
+  *buff = '\0';
+  return result;
+}
+
+
+int snprintf(char * buff, sos_size_t len, const char *format, ...)
+{
+  va_list ap;
+ 
+  va_start(ap, format);
+  len = vsnprintf(buff, len, format, ap);
+  va_end(ap);
+ 
+  return len;
+}
diff --git a/sos-code-article4/sos/klibc.h b/sos-code-article4/sos/klibc.h
new file mode 100644
index 0000000..a8b9d49
--- /dev/null
+++ b/sos-code-article4/sos/klibc.h
@@ -0,0 +1,84 @@
+/* Copyright (C) 2003  The KOS Team
+   Copyright (C) 1999  Free Software Foundation
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#ifndef _SOS_KLIBC_H_
+#define _SOS_KLIBC_H_
+
+/**
+ * @file klibc.h
+ *
+ * Basic libc-style support for common useful functions (string.h,
+ * stdarg.h), some with slight non-standard behavior (see comments).
+ */
+
+#include <sos/types.h>
+
+/* string.h functions */
+
+void *memcpy(void *dst, const void *src, register unsigned int size ) ;
+void *memset(void *dst, register int c, register unsigned int length ) ;
+int memcmp(const void *s1, const void *s2, sos_size_t n);
+
+unsigned int strlen( register const char *str) ;
+unsigned int strnlen(const char * s, sos_size_t maxlen);
+
+/**
+ * @note Same as strncpy(), with a slightly different semantic.
+ * Actually, strncpy(3C) says " The result will not be null-terminated
+ * if the length of 'from' is n or more.".  Here, 'dst' is ALWAYS
+ * null-terminated. And its total len will ALWAYS be <= len, with
+ * null-terminating-char included.
+ */
+char *strzcpy( register char *dst, register const char *src,
+               register int len ) ;
+
+/**
+ * @note Same as strncat(), with the same semantic : 'dst' is ALWAYS
+ * null-terminated. And its total len will ALWAYS be <= len, with
+ * null-terminating-char included.
+ */
+char *strzcat (char *dest, const char *src,
+               const sos_size_t len);
+ 
+int strcmp(register const char *s1, register const char *s2 );
+int strncmp(register const char *s1, register const char *s2,
+	    register int len );
+
+/* Basic stdarg.h macros. Taken from gcc support files */
+#define __GNUC_VA_LIST 
+typedef void *__gnuc_va_list;
+typedef __gnuc_va_list va_list;
+#define __va_rounded_size(TYPE) \
+  (((sizeof (TYPE) + sizeof (int) - 1) / sizeof (int)) * sizeof (int))
+#define va_start(AP, LASTARG) \
+  (AP = ((__gnuc_va_list) __builtin_next_arg (LASTARG)))
+#define va_end(AP) \
+  ((void)0)
+#define va_arg(AP, TYPE) \
+  (AP = (__gnuc_va_list) ((char *) (AP) + __va_rounded_size (TYPE)),  \
+   *((TYPE *) (void *) ((char *) (AP) - __va_rounded_size (TYPE))))
+#define __va_copy(dest, src) \
+  (dest) = (src)
+
+/* stdarg.h functions. There might be a non-standard behavior: there
+   will always be a trailing '\0' in the resulting string */
+int vsnprintf(char *, sos_size_t, const char *, va_list);
+int snprintf(char *, sos_size_t, const char *, /*args*/ ...)
+  __attribute__ ((format (printf, 3, 4)));
+
+#endif /* _SOS_KLIBC_H_ */
diff --git a/sos-code-article4/sos/list.h b/sos-code-article4/sos/list.h
new file mode 100644
index 0000000..67e72f3
--- /dev/null
+++ b/sos-code-article4/sos/list.h
@@ -0,0 +1,186 @@
+/* Copyright (C) 2001  David Decotigny
+ 
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+    
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+    
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA.
+*/
+#ifndef _SOS_LIST_H_
+#define _SOS_LIST_H_
+
+/**
+ * @file list.h
+ *
+ * Circular doubly-linked lists implementation entirely based on C
+ * macros
+ */
+
+
+/* *_named are used when next and prev links are not exactly next
+   and prev. For instance when we have next_in_team, prev_in_team,
+   prev_global and next_global */
+
+#define list_init_named(list,prev,next) \
+  ((list) = NULL)
+
+#define list_singleton_named(list,item,prev,next) ({ \
+  (item)->next = (item)->prev = (item); \
+  (list) = (item); \
+})
+
+#define list_is_empty_named(list,prev,next) \
+  ((list) == NULL)
+
+#define list_get_head_named(list,prev,next) \
+  (list)
+
+#define list_get_tail_named(list,prev,next) \
+  ((list)?((list)->prev):NULL)
+
+/* Internal macro : insert before the head == insert at tail */
+#define __list_insert_atleft_named(before_this,item,prev,next) ({ \
+   (before_this)->prev->next = (item); \
+   (item)->prev = (before_this)->prev; \
+   (before_this)->prev = (item); \
+   (item)->next = (before_this); \
+})
+
+/* @note Before_this and item are expected to be valid ! */
+#define list_insert_before_named(list,before_this,item,prev,next) ({ \
+   __list_insert_atleft_named(before_this,item,prev,next); \
+   if ((list) == (before_this)) (list) = (item); \
+})    
+
+/** @note After_this and item are expected to be valid ! */
+#define list_insert_after_named(list,after_this,item,prev,next) ({ \
+   (after_this)->next->prev = (item); \
+   (item)->next = (after_this)->next; \
+   (after_this)->next = (item); \
+   (item)->prev = (after_this); \
+})
+
+#define list_add_head_named(list,item,prev,next) ({ \
+  if (list) \
+    list_insert_before_named(list,list,item,prev,next); \
+  else \
+    list_singleton_named(list,item,prev,next); \
+  (list) = (item); \
+})
+
+#define list_add_tail_named(list,item,prev,next) ({ \
+  if (list) \
+    __list_insert_atleft_named(list,item,prev,next); \
+  else \
+    list_singleton_named(list,item,prev,next); \
+})
+
+/** @note NO check whether item really is in list ! */
+#define list_delete_named(list,item,prev,next) ({ \
+  if ( ((item)->next == (item)) && ((item)->prev == (item)) ) \
+    (item)->next = (item)->prev = (list) = NULL; \
+  else { \
+    (item)->prev->next = (item)->next; \
+    (item)->next->prev = (item)->prev; \
+    if ((item) == (list)) (list) = (item)->next; \
+    (item)->prev = (item)->next = NULL; \
+  } \
+})
+
+#define list_pop_head_named(list,prev,next) ({ \
+  typeof(list) __ret_elt = (list); \
+  list_delete_named(list,__ret_elt,prev,next); \
+  __ret_elt; })
+
+/** Loop statement that iterates through all of its elements, from
+    head to tail */
+#define list_foreach_forward_named(list,iterator,nb_elements,prev,next) \
+        for (nb_elements=0, (iterator) = (list) ; \
+             (iterator) && (!nb_elements || ((iterator) != (list))) ; \
+             nb_elements++, (iterator) = (iterator)->next )
+
+/** Loop statement that iterates through all of its elements, from
+    tail back to head */
+#define list_foreach_backward_named(list,iterator,nb_elements,prev,next) \
+        for (nb_elements=0, (iterator) = list_get_tail_named(list,prev,next) ; \
+             (iterator) && (!nb_elements || \
+               ((iterator) != list_get_tail_named(list,prev,next))) ; \
+             nb_elements++, (iterator) = (iterator)->prev )
+
+#define list_foreach_named list_foreach_forward_named
+
+/** True when we exitted early from the foreach loop (ie break) */
+#define list_foreach_early_break(list,iterator,nb_elements) \
+  ((list) && ( \
+    ((list) != (iterator)) || \
+    ( ((list) == (iterator)) && (nb_elements == 0)) ))
+
+/** Loop statement that also removes the item at each iteration */
+#define list_collapse_named(list,iterator,prev,next) \
+        for ( ; ({ ((iterator) = (list)) ; \
+                   if (list) list_delete_named(list,iterator,prev,next) ; \
+                   (iterator); }) ; )
+
+
+/*
+ * the same macros : assume that the prev and next fields are really
+ * named "prev" and "next"
+ */
+
+#define list_init(list) \
+  list_init_named(list,prev,next)
+
+#define list_singleton(list,item) \
+  list_singleton_named(list,item,prev,next)
+
+#define list_is_empty(list) \
+  list_is_empty_named(list,prev,next)
+
+#define list_get_head(list) \
+  list_get_head_named(list,prev,next) \
+
+#define list_get_tail(list) \
+  list_get_tail_named(list,prev,next) \
+
+/* @note Before_this and item are expected to be valid ! */
+#define list_insert_after(list,after_this,item) \
+  list_insert_after_named(list,after_this,item,prev,next)
+
+/* @note After_this and item are expected to be valid ! */
+#define list_insert_before(list,before_this,item) \
+  list_insert_before_named(list,before_this,item,prev,next)
+
+#define list_add_head(list,item) \
+  list_add_head_named(list,item,prev,next)
+
+#define list_add_tail(list,item) \
+  list_add_tail_named(list,item,prev,next)
+
+/* @note NO check whether item really is in list ! */
+#define list_delete(list,item) \
+  list_delete_named(list,item,prev,next)
+
+#define list_pop_head(list) \
+  list_pop_head_named(list,prev,next)
+
+#define list_foreach_forward(list,iterator,nb_elements) \
+  list_foreach_forward_named(list,iterator,nb_elements,prev,next)
+
+#define list_foreach_backward(list,iterator,nb_elements) \
+  list_foreach_backward_named(list,iterator,nb_elements,prev,next)
+
+#define list_foreach list_foreach_forward
+
+#define list_collapse(list,iterator) \
+  list_collapse_named(list,iterator,prev,next)
+
+#endif /* _SOS_LIST_H_ */
diff --git a/sos-code-article4/sos/macros.h b/sos-code-article4/sos/macros.h
new file mode 100644
index 0000000..b08f081
--- /dev/null
+++ b/sos-code-article4/sos/macros.h
@@ -0,0 +1,37 @@
+/* Copyright (C) 2004  The KOS Team
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#ifndef _SOS_MACROS_H_
+#define _SOS_MACROS_H_
+
+/** Align on a boundary (MUST be a power of 2), so that return value <= val */
+#define SOS_ALIGN_INF(val,boundary) \
+  (((unsigned)(val)) & (~((boundary)-1)))
+ 
+/** Align on a boundary (MUST be a power of 2), so that return value >= val */
+#define SOS_ALIGN_SUP(val,boundary) \
+  ({ unsigned int __bnd=(boundary); \
+     (((((unsigned)(val))-1) & (~(__bnd - 1))) + __bnd); })
+
+/**
+ * @return TRUE if val is a power of 2.
+ * @note val is evaluated multiple times
+ */
+#define SOS_IS_POWER_OF_2(val) \
+  ((((val) - 1) & (val)) == 0)
+
+#endif /* _SOS_MACROS_H_ */
diff --git a/sos-code-article4/sos/main.c b/sos-code-article4/sos/main.c
new file mode 100644
index 0000000..7f54f70
--- /dev/null
+++ b/sos-code-article4/sos/main.c
@@ -0,0 +1,298 @@
+/* Copyright (C) 2004  The SOS Team
+   Copyright (C) 1999  Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+
+/* Include definitions of the multiboot standard */
+#include <bootstrap/multiboot.h>
+#include <hwcore/idt.h>
+#include <hwcore/gdt.h>
+#include <hwcore/irq.h>
+#include <hwcore/exception.h>
+#include <hwcore/i8254.h>
+#include <sos/list.h>
+#include <sos/physmem.h>
+#include <hwcore/paging.h>
+#include <sos/list.h>
+#include <sos/klibc.h>
+#include <sos/assert.h>
+#include <drivers/x86_videomem.h>
+#include <drivers/bochs.h>
+
+
+/* Helper function to display each bits of a 32bits integer on the
+   screen as dark or light carrets */
+static void display_bits(unsigned char row, unsigned char col,
+			 unsigned char attribute,
+			 sos_ui32_t integer)
+{
+  int i;
+  /* Scan each bit of the integer, MSb first */
+  for (i = 31 ; i >= 0 ; i--)
+    {
+      /* Test if bit i of 'integer' is set */
+      int bit_i = (integer & (1 << i));
+      /* Ascii 219 => dark carret, Ascii 177 => light carret */
+      unsigned char ascii_code = bit_i?219:177;
+      sos_x86_videomem_putchar(row, col++,
+			       attribute,
+			       ascii_code);
+    }
+}
+
+
+/* Clock IRQ handler */
+static void clk_it(int intid)
+{
+  static sos_ui32_t clock_count = 0;
+
+  display_bits(0, 48,
+	       SOS_X86_VIDEO_FG_LTGREEN | SOS_X86_VIDEO_BG_BLUE,
+	       clock_count);
+  clock_count++;
+
+}
+
+/* Page fault exception handler */
+static void pgflt_ex(int exid)
+{
+  sos_bochs_printf("Got page fault\n");
+  sos_x86_videomem_printf(10, 30,
+			  SOS_X86_VIDEO_FG_LTRED | SOS_X86_VIDEO_BG_BLUE,
+			  "Got EXPECTED (?) Page fault ! But where ???");
+  for (;;) ;
+}
+
+static void test_paging(sos_vaddr_t sos_kernel_core_top_vaddr)
+{
+  /* The (linear) address of the page holding the code we are
+     currently executing */
+  sos_vaddr_t vpage_code = SOS_PAGE_ALIGN_INF(test_paging);
+
+  /* The new physical page that will hold the code */
+  sos_paddr_t ppage_new;
+
+  /* Where this page will be mapped temporarily in order to copy the
+     code into it: right after the kernel code/data */
+  sos_vaddr_t vpage_tmp = sos_kernel_core_top_vaddr;
+
+  unsigned i;
+
+  /* Bind the page fault exception to one of our routines */
+  sos_exception_set_routine(SOS_EXCEPT_PAGE_FAULT,
+			    pgflt_ex);
+
+  /*
+   * Test 1: move the page where we execute the code elsewhere in
+   * physical memory
+   */
+  sos_x86_videomem_printf(4, 0,
+			  SOS_X86_VIDEO_FG_LTGREEN | SOS_X86_VIDEO_BG_BLUE,
+			  "Moving current code elsewhere in physical memory:");
+
+
+  /* Allocate a new physical page */
+  ppage_new = sos_physmem_ref_physpage_new(FALSE);
+  if (! ppage_new)
+    {
+      /* STOP ! No memory left */
+      sos_x86_videomem_putstring(20, 0,
+				 SOS_X86_VIDEO_FG_LTRED
+				   | SOS_X86_VIDEO_BG_BLUE,
+				 "test_paging : Cannot allocate page");
+      return;
+    }
+
+  sos_x86_videomem_printf(5, 0,
+			  SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			  "Hello from the address 0x%x in physical memory",
+			  sos_paging_get_paddr(vpage_code));
+
+  sos_x86_videomem_printf(6, 0,
+			  SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			  "Transfer vpage 0x%x: ppage 0x%x -> 0x%x (tmp vpage 0x%x)",
+	                  vpage_code,
+			  sos_paging_get_paddr(vpage_code),
+			  ppage_new,
+			  (unsigned)vpage_tmp);
+
+  /* Map the page somewhere (right after the kernel mapping) in order
+     to copy the code we are currently executing */
+  sos_paging_map(ppage_new, vpage_tmp,
+		 FALSE,
+		 SOS_VM_MAP_ATOMIC
+		 | SOS_VM_MAP_PROT_READ
+		 | SOS_VM_MAP_PROT_WRITE);
+
+  /* Ok, the new page is referenced by the mapping, we can release our
+     reference to it */
+  sos_physmem_unref_physpage(ppage_new);
+
+  /* Copy the contents of the current page of code to this new page
+     mapping */
+  memcpy((void*)vpage_tmp,
+	 (void*)vpage_code,
+	 SOS_PAGE_SIZE);
+
+  /* Transfer the mapping of the current page of code to this new page */
+  sos_paging_map(ppage_new, vpage_code,
+		 FALSE,
+		 SOS_VM_MAP_ATOMIC
+		 | SOS_VM_MAP_PROT_READ
+		 | SOS_VM_MAP_PROT_WRITE);
+  
+  /* Ok, here we are: we have changed the physcal page that holds the
+     code we are executing ;). However, this new page is mapped at 2
+     virtual addresses:
+     - vpage_tmp
+     - vpage_code
+     We can safely unmap it from sos_kernel_core_top_vaddr, while
+     still keeping the vpage_code mapping */
+  sos_paging_unmap(vpage_tmp);
+
+  sos_x86_videomem_printf(7, 0,
+			  SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			  "Hello from the address 0x%x in physical memory",
+			  sos_paging_get_paddr(vpage_code));
+
+  sos_x86_videomem_printf(9, 0,
+			  SOS_X86_VIDEO_FG_LTGREEN | SOS_X86_VIDEO_BG_BLUE,
+			  "Provoking a page fault:");
+
+  /*
+   * Test 2: make sure the #PF handler works
+   */
+
+  /* Scan part of the kernel up to a page fault. This page fault
+     should occur on the first page unmapped after the kernel area,
+     which is exactly the page we temporarily mapped/unmapped
+     (vpage_tmp) above to move the kernel code we are executing */
+  for (i = vpage_code ; /* none */ ; i += SOS_PAGE_SIZE)
+    {
+      unsigned *pint = (unsigned *)SOS_PAGE_ALIGN_INF(i);
+      sos_bochs_printf("Test vaddr 0x%x : val=", (unsigned)pint);
+      sos_x86_videomem_printf(10, 0,
+			      SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			      "Test vaddr 0x%x : val=      ",
+			      (unsigned)pint);
+      sos_bochs_printf("0x%x\n", *pint);
+      sos_x86_videomem_printf(10, 30,
+			      SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			      "0x%x          ", *pint);
+    }
+
+  /* BAD ! Did not get the page fault... */
+  sos_x86_videomem_printf(20, 0,
+			  SOS_X86_VIDEO_FG_LTRED | SOS_X86_VIDEO_BG_BLUE,
+			  "We should have had a #PF at vaddr 0x%x !",
+			  vpage_tmp);
+}
+
+/* The C entry point of our operating system */
+void sos_main(unsigned long magic, unsigned long addr)
+{
+  unsigned i;
+  sos_paddr_t sos_kernel_core_base_paddr, sos_kernel_core_top_paddr;
+
+  /* Grub sends us a structure, called multiboot_info_t with a lot of
+     precious informations about the system, see the multiboot
+     documentation for more information. */
+  multiboot_info_t *mbi;
+  mbi = (multiboot_info_t *) addr;
+
+  /* Setup bochs and console, and clear the console */
+  sos_bochs_setup();
+
+  sos_x86_videomem_setup();
+  sos_x86_videomem_cls(SOS_X86_VIDEO_BG_BLUE);
+
+  /* Greetings from SOS */
+  if (magic == MULTIBOOT_BOOTLOADER_MAGIC)
+    /* Loaded with Grub */
+    sos_x86_videomem_printf(1, 0,
+			    SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			    "Welcome From GRUB to %s%c RAM is %dMB (upper mem = 0x%x kB)",
+			    "SOS", ',',
+			    (unsigned)(mbi->mem_upper >> 10) + 1,
+			    (unsigned)mbi->mem_upper);
+  else
+    /* Not loaded with grub */
+    sos_x86_videomem_printf(1, 0,
+			    SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			    "Welcome to SOS");
+
+  sos_bochs_putstring("Message in a bochs\n");
+
+  /* Setup CPU segmentation and IRQ subsystem */
+  sos_gdt_setup();
+  sos_idt_setup();
+
+  /* Setup SOS IRQs and exceptions subsystem */
+  sos_exceptions_setup();
+  sos_irq_setup();
+
+  /* Configure the timer so as to raise the IRQ0 at a 100Hz rate */
+  sos_i8254_set_frequency(100);
+
+
+  /* We need a multiboot-compliant boot loader to get the size of the RAM */
+  if (magic != MULTIBOOT_BOOTLOADER_MAGIC)
+    {
+      sos_x86_videomem_putstring(20, 0,
+				 SOS_X86_VIDEO_FG_LTRED
+				   | SOS_X86_VIDEO_BG_BLUE
+				   | SOS_X86_VIDEO_FG_BLINKING,
+				 "I'm not loaded with Grub !");
+      /* STOP ! */
+      for (;;)
+	continue;
+    }
+
+  /* Binding some HW interrupts and exceptions to software routines */
+  sos_irq_set_routine(SOS_IRQ_TIMER,
+			    clk_it);
+  /* Enabling the HW interrupts here, this will make the timer HW
+     interrupt call our clk_it handler */
+  asm volatile ("sti\n");
+  /* Multiboot says: "The value returned for upper memory is maximally
+     the address of the first upper memory hole minus 1 megabyte.". It
+     also adds: "It is not guaranteed to be this value." aka "YMMV" ;) */
+  sos_physmem_setup((mbi->mem_upper<<10) + (1<<20),
+		    & sos_kernel_core_base_paddr,
+		    & sos_kernel_core_top_paddr);
+  
+  /*
+   * Switch to paged-memory mode
+   */
+
+  /* Disabling interrupts should seem more correct, but it's not really
+     necessary at this stage */
+  if (sos_paging_setup(sos_kernel_core_base_paddr,
+		       sos_kernel_core_top_paddr))
+    sos_bochs_printf("Could not setup paged memory mode\n");
+  sos_x86_videomem_printf(2, 0,
+			  SOS_X86_VIDEO_FG_YELLOW | SOS_X86_VIDEO_BG_BLUE,
+			  "Paged-memory mode is activated");
+
+  test_paging(sos_kernel_core_top_paddr);
+
+  /* An operatig system never ends */
+  for (;;)
+    continue;
+
+  return;
+}
diff --git a/sos-code-article4/sos/physmem.c b/sos-code-article4/sos/physmem.c
new file mode 100644
index 0000000..99cffb7
--- /dev/null
+++ b/sos-code-article4/sos/physmem.c
@@ -0,0 +1,269 @@
+/* Copyright (C) 2004  David Decotigny
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#include <sos/list.h>
+#include <sos/macros.h>
+#include <sos/assert.h>
+#include <sos/klibc.h>
+
+#include "physmem.h"
+
+/** A descriptor for a physical page in SOS */
+struct physical_page_descr
+{
+  /** The physical base address for the page */
+  sos_paddr_t paddr;
+
+  /** The reference count for this physical page. > 0 means that the
+     page is in the used list. */
+  sos_count_t ref_cnt;
+
+  /** The other pages on the list (used, free) */
+  struct physical_page_descr *prev, *next;
+};
+
+/** These are some markers present in the executable file (see sos.lds) */
+extern char __b_kernel, __e_kernel;
+
+/** The array of ppage descriptors will be located at this address */
+#define PAGE_DESCR_ARRAY_ADDR \
+  SOS_PAGE_ALIGN_SUP((sos_paddr_t) (& __e_kernel))
+static struct physical_page_descr * physical_page_descr_array;
+
+/** The list of physical pages currently available */
+static struct physical_page_descr *free_ppage;
+
+/** The list of physical pages currently in use */
+static struct physical_page_descr *used_ppage;
+
+/** We will store here the interval of valid physical addresses */
+static sos_paddr_t physmem_base, physmem_top;
+
+/** We store the number of pages used/free */
+static sos_count_t physmem_total_pages, physmem_used_pages;
+
+sos_ret_t sos_physmem_setup(sos_size_t ram_size,
+			    /* out */sos_paddr_t *kernel_core_base,
+			    /* out */sos_paddr_t *kernel_core_top)
+{
+  /* The iterator over the page descriptors */
+  struct physical_page_descr *ppage_descr;
+
+  /* The iterator over the physical addresses */
+  sos_paddr_t ppage_addr;
+
+  /* Make sure ram size is aligned on a page boundary */
+  ram_size = SOS_PAGE_ALIGN_INF(ram_size);/* Yes, we may lose at most a page */
+
+  /* Reset the used/free page lists before building them */
+  free_ppage = used_ppage = NULL;
+  physmem_total_pages = physmem_used_pages = 0;
+
+  /* Make sure that there is enough memory to store the array of page
+     descriptors */
+  *kernel_core_base = SOS_PAGE_ALIGN_INF((sos_paddr_t)(& __b_kernel));
+  *kernel_core_top
+    = PAGE_DESCR_ARRAY_ADDR
+      + SOS_PAGE_ALIGN_SUP( (ram_size >> SOS_PAGE_SHIFT)
+			    * sizeof(struct physical_page_descr));
+  if (*kernel_core_top > ram_size)
+    return -SOS_ENOMEM;
+
+  /* Page 0-4kB is not available in order to return address 0 as a
+     means to signal "no page available" */
+  physmem_base = SOS_PAGE_SIZE;
+  physmem_top  = ram_size;
+
+  /* Setup the page descriptor arrray */
+  physical_page_descr_array
+    = (struct physical_page_descr*)PAGE_DESCR_ARRAY_ADDR;
+
+  /* Scan the list of physical pages */
+  for (ppage_addr = 0,
+	 ppage_descr = physical_page_descr_array ;
+       ppage_addr < physmem_top ;
+       ppage_addr += SOS_PAGE_SIZE,
+	 ppage_descr ++)
+    {
+      enum { PPAGE_MARK_RESERVED, PPAGE_MARK_FREE,
+	     PPAGE_MARK_KERNEL, PPAGE_MARK_HWMAP } todo;
+
+      memset(ppage_descr, 0x0, sizeof(struct physical_page_descr));
+
+      /* Init the page descriptor for this page */
+      ppage_descr->paddr = ppage_addr;
+
+      /* Reserved : 0 ... base */
+      if (ppage_addr < physmem_base)
+	todo = PPAGE_MARK_RESERVED;
+
+      /* Free : base ... BIOS */
+      else if ((ppage_addr >= physmem_base)
+	       && (ppage_addr < BIOS_N_VIDEO_START))
+	todo = PPAGE_MARK_FREE;
+
+      /* Used : BIOS */
+      else if ((ppage_addr >= BIOS_N_VIDEO_START)
+	       && (ppage_addr < BIOS_N_VIDEO_END))
+	todo = PPAGE_MARK_HWMAP;
+
+      /* Free : BIOS ... kernel */
+      else if ((ppage_addr >= BIOS_N_VIDEO_END)
+	       && (ppage_addr < (sos_paddr_t) (& __b_kernel)))
+	todo = PPAGE_MARK_FREE;
+
+      /* Used : Kernel code/data/bss + physcal page descr array */
+      else if ((ppage_addr >= *kernel_core_base)
+		&& (ppage_addr < *kernel_core_top))
+	todo = PPAGE_MARK_KERNEL;
+
+      /* Free : first page of descr ... end of RAM */
+      else
+	todo = PPAGE_MARK_FREE;
+
+      /* Actually does the insertion in the used/free page lists */
+      physmem_total_pages ++;
+      switch (todo)
+	{
+	case PPAGE_MARK_FREE:
+	  ppage_descr->ref_cnt = 0;
+	  list_add_head(free_ppage, ppage_descr);
+	  break;
+
+	case PPAGE_MARK_KERNEL:
+	case PPAGE_MARK_HWMAP:
+	  ppage_descr->ref_cnt = 1;
+	  list_add_head(used_ppage, ppage_descr);
+	  physmem_used_pages ++;
+	  break;
+
+	default:
+	  /* Reserved page: nop */
+	  break;
+	}
+    }
+
+  return SOS_OK;
+}
+
+
+sos_paddr_t sos_physmem_ref_physpage_new(sos_bool_t can_block)
+{
+  struct physical_page_descr *ppage_descr;
+
+  if (! free_ppage)
+    return (sos_paddr_t)NULL;
+
+  /* Retrieve a page in the free list */
+  ppage_descr = list_pop_head(free_ppage);
+
+  /* The page is assumed not to be already used */
+  SOS_ASSERT_FATAL(ppage_descr->ref_cnt == 0);
+
+  /* Mark the page as used (this of course sets the ref count to 1) */
+  ppage_descr->ref_cnt ++;
+
+  /* Put the page in the used list */
+  list_add_tail(used_ppage, ppage_descr);
+  physmem_used_pages ++;
+
+  return ppage_descr->paddr;
+}
+
+
+/**
+ * Helper function to get the physical page descriptor for the given
+ * physical page address.
+ *
+ * @return NULL when out-of-bounds or non-page-aligned
+ */
+inline static struct physical_page_descr *
+get_page_descr_at_paddr(sos_paddr_t ppage_paddr)
+{
+  /* Don't handle non-page-aligned addresses */
+  if (ppage_paddr & SOS_PAGE_MASK)
+    return NULL;
+  
+  /* Don't support out-of-bounds requests */
+  if ((ppage_paddr < physmem_base) || (ppage_paddr >= physmem_top))
+    return NULL;
+
+  return physical_page_descr_array + (ppage_paddr >> SOS_PAGE_SHIFT);
+}
+
+
+sos_ret_t sos_physmem_ref_physpage_at(sos_paddr_t ppage_paddr)
+{
+  struct physical_page_descr *ppage_descr
+    = get_page_descr_at_paddr(ppage_paddr);
+
+  if (! ppage_descr)
+    return -SOS_EINVAL;
+
+  /* Increment the reference count for the page */
+  ppage_descr->ref_cnt ++;
+
+  /* If the page is newly referenced (ie we are the only owners of the
+     page => ref cnt == 1), transfer it in the used pages list */
+  if (ppage_descr->ref_cnt == 1)
+    {
+      list_delete(free_ppage, ppage_descr);
+      list_add_tail(used_ppage, ppage_descr);
+      physmem_used_pages ++;
+
+      /* The page is newly referenced */
+      return FALSE;
+    }
+
+  /* The page was already referenced by someone */
+  return TRUE;
+}
+
+
+sos_ret_t
+sos_physmem_unref_physpage(sos_paddr_t ppage_paddr)
+{
+  /* By default the return value indicates that the page is still
+     used */
+  sos_ret_t retval = FALSE;
+
+  struct physical_page_descr *ppage_descr
+    = get_page_descr_at_paddr(ppage_paddr);
+
+  if (! ppage_descr)
+    return -SOS_EINVAL;
+
+  /* Don't do anything if the page is not in the used list */
+  if (ppage_descr->ref_cnt <= 0)
+    return -SOS_EINVAL;
+
+  /* Unreference the page, and, when no mapping is active anymore, put
+     the page in the free list */
+  ppage_descr->ref_cnt--;
+  if (ppage_descr->ref_cnt <= 0)
+    {
+      /* Transfer the page, considered USED, to the free list */
+      list_delete(used_ppage, ppage_descr);
+      physmem_used_pages --;
+      list_add_head(free_ppage, ppage_descr);
+
+      /* Indicate that the page is now unreferenced */
+      retval = TRUE;
+    }
+
+  return retval;
+}
diff --git a/sos-code-article4/sos/physmem.h b/sos-code-article4/sos/physmem.h
new file mode 100644
index 0000000..8b5d997
--- /dev/null
+++ b/sos-code-article4/sos/physmem.h
@@ -0,0 +1,119 @@
+/* Copyright (C) 2004  David Decotigny
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#ifndef _SOS_PHYSMEM_H_
+#define _SOS_PHYSMEM_H_
+
+/**
+ * @file physmem.h
+ *
+ * Physical pages of memory
+ */
+
+#include <sos/errno.h>
+#include <sos/types.h>
+#include <sos/macros.h>
+
+/** The size of a physical page (arch-dependent) */
+#define SOS_PAGE_SIZE  (4*1024)
+
+/** The corresponding shift */
+#define SOS_PAGE_SHIFT 12 /* 4 kB = 2^12 B */
+
+/** The corresponding mask */
+#define SOS_PAGE_MASK  ((1<<12) - 1)
+
+#define SOS_PAGE_ALIGN_INF(val) \
+  SOS_ALIGN_INF((val), SOS_PAGE_SIZE)
+#define SOS_PAGE_ALIGN_SUP(val) \
+  SOS_ALIGN_SUP((val), SOS_PAGE_SIZE)
+
+
+/**
+ * This is the reserved physical interval for the x86 video memory and
+ * BIOS area. In physmem.c, we have to mark this area as "used" in
+ * order to prevent from allocating it. And in paging.c, we'd better
+ * map it in virtual space if we really want to be able to print to
+ * the screen (for debugging purpose, at least): for this, the
+ * simplest is to identity-map this area in virtual space (note
+ * however that this mapping could also be non-identical).
+ */
+#define BIOS_N_VIDEO_START 0xa0000
+#define BIOS_N_VIDEO_END   0x100000
+
+
+/**
+ * Initialize the physical memory subsystem, for the physical area [0,
+ * ram_size). This routine takes into account the BIOS and video
+ * areas, to prevent them from future allocations.
+ *
+ * @param ram_size The size of the RAM that will be managed by this subsystem
+ *
+ * @param kernel_core_base The lowest address for which the kernel
+ * assumes identity mapping (ie virtual address == physical address)
+ * will be stored here
+ *
+ * @param kernel_core_top The top address for which the kernel
+ * assumes identity mapping (ie virtual address == physical address)
+ * will be stored here
+ */
+sos_ret_t sos_physmem_setup(sos_size_t ram_size,
+			    /* out */sos_paddr_t *kernel_core_base,
+			    /* out */sos_paddr_t *kernel_core_top);
+
+/**
+ * Retrieve the total number of pages, and the number of free pages
+ */
+sos_ret_t sos_physmem_get_state(/* out */sos_count_t *total_ppages,
+				/* out */sos_count_t *used_ppages);
+
+
+/**
+ * Get a free page.
+ *
+ * @return The (physical) address of the (physical) page allocated, or
+ * NULL when none currently available.
+ *
+ * @param can_block TRUE if the function is allowed to block
+ * @note The page returned has a reference count equal to 1.
+ */
+sos_paddr_t sos_physmem_ref_physpage_new(sos_bool_t can_block);
+
+
+/**
+ * Increment the reference count of a given physical page. Useful for
+ * VM code which tries to map a precise physical address.
+ *
+ * @return TRUE when the page was previously in use, FALSE when the
+ * page was previously in the free list, <0 when the page address is
+ * invalid.
+ */
+sos_ret_t sos_physmem_ref_physpage_at(sos_paddr_t ppage_paddr);
+
+
+/**
+ * Decrement the reference count of the given physical page. When this
+ * reference count reaches 0, the page is marked free, ie is available
+ * for future sos_physmem_get_physpage()
+ *
+ * @return FALSE when the page is still in use, TRUE when the page is now
+ * unreferenced, <0 when the page address is invalid
+ */
+sos_ret_t sos_physmem_unref_physpage(sos_paddr_t ppage_paddr);
+
+
+#endif /* _SOS_PHYSMEM_H_ */
diff --git a/sos-code-article4/sos/types.h b/sos-code-article4/sos/types.h
new file mode 100644
index 0000000..02d9f6d
--- /dev/null
+++ b/sos-code-article4/sos/types.h
@@ -0,0 +1,50 @@
+/* Copyright (C) 2004  The SOS Team
+   Copyright (C) 1999  Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; either version 2
+   of the License, or (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+   USA. 
+*/
+#ifndef _SOS_TYPES_H_
+#define _SOS_TYPES_H_
+
+/**
+ * @file types.h
+ *
+ * SOS basic types definition
+ */
+
+/** Physical address */
+typedef unsigned int       sos_paddr_t;
+
+/** Generic virtual address (kernel or user) */
+typedef unsigned int       sos_vaddr_t;
+
+/** Memory size of an object (positive) */
+typedef unsigned int       sos_size_t;
+/** Generic count of objects */
+typedef unsigned int       sos_count_t;
+
+/** Low-level sizes */
+typedef unsigned long int  sos_ui32_t; /* 32b unsigned */
+typedef unsigned short int sos_ui16_t; /* 16b unsigned */
+typedef unsigned char      sos_ui8_t;  /* 8b unsigned */
+
+typedef enum { FALSE=0, TRUE } sos_bool_t;
+
+/** Not a proper type, but highly useful with basic type
+    manipulations */
+#define NULL ((void*)0)
+
+#endif /* _SOS_TYPES_H_ */