4 files changed, 9 insertions, 7 deletions
diff --git a/kernel/defs.h b/kernel/defs.h
index 9c5f643..f33f1f6 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -52,6 +52,7 @@ struct inode*   nameiparent(char*, char*);
 int             readi(struct inode*, int, uint64, uint, uint);
 void            stati(struct inode*, struct stat*);
 int             writei(struct inode*, int, uint64, uint, uint);
+void            itrunc(struct inode*);
 
 // ramdisk.c
 void            ramdiskinit(void);
diff --git a/kernel/fcntl.h b/kernel/fcntl.h
index d565483..44861b9 100644
--- a/kernel/fcntl.h
+++ b/kernel/fcntl.h
@@ -2,3 +2,4 @@
 #define O_WRONLY  0x001
 #define O_RDWR    0x002
 #define O_CREATE  0x200
+#define O_TRUNC   0x400
diff --git a/kernel/fs.c b/kernel/fs.c
index 53586d5..e33ec30 100644
--- a/kernel/fs.c
+++ b/kernel/fs.c
@@ -22,7 +22,6 @@
 #include "file.h"
 
 #define min(a, b) ((a) < (b) ? (a) : (b))
-static void itrunc(struct inode*);
 // there should be one superblock per disk device, but we run with
 // only one device
 struct superblock sb; 
@@ -406,11 +405,8 @@ bmap(struct inode *ip, uint bn)
 }
 
 // Truncate inode (discard contents).
-// Only called when the inode has no links
-// to it (no directory entries referring to it)
-// and has no in-memory reference to it (is
-// not an open file or current directory).
-static void
+// Caller must hold ip->lock.
+void
 itrunc(struct inode *ip)
 {
   int i, j;
@@ -463,7 +459,7 @@ readi(struct inode *ip, int user_dst, uint64 dst, uint off, uint n)
   struct buf *bp;
 
   if(off > ip->size || off + n < off)
-    return -1;
+    return 0;
   if(off + n > ip->size)
     n = ip->size - off;
 
diff --git a/kernel/sysfile.c b/kernel/sysfile.c
index 7768d20..015c942 100644
--- a/kernel/sysfile.c
+++ b/kernel/sysfile.c
@@ -341,6 +341,10 @@ sys_open(void)
   f->readable = !(omode & O_WRONLY);
   f->writable = (omode & O_WRONLY) || (omode & O_RDWR);
 
+  if((omode & O_TRUNC) && ip->type == T_FILE){
+    itrunc(ip);
+  }
+
   iunlock(ip);
   end_op();