Add symlink syscall

Makefile

@@ -188,6 +188,7 @@ UPROGS=\
 	$U/_grind\
 	$U/_wc\
 	$U/_zombie\
+	$U/_symlinktest
 
 
 

kernel/fcntl.h

@@ -1,5 +1,6 @@
-#define O_RDONLY  0x000
-#define O_WRONLY  0x001
-#define O_RDWR    0x002
-#define O_CREATE  0x200
-#define O_TRUNC   0x400
+#define O_RDONLY   0x000
+#define O_WRONLY   0x001
+#define O_RDWR     0x002
+#define O_CREATE   0x200
+#define O_TRUNC    0x400
+#define O_NOFOLLOW 0x008

kernel/file.h

@@ -27,6 +27,7 @@ struct inode {
   short nlink;
   uint size;
   uint addrs[NDIRECT+2];
+  char path[128]; // MAXPATH = 128
 };
 
 // map major device number to device functions.

kernel/stat.h

@@ -1,6 +1,7 @@
 #define T_DIR     1   // Directory
 #define T_FILE    2   // File
 #define T_DEVICE  3   // Device
+#define T_SYMLINK 4   // Symbolic Link
 
 struct stat {
   int dev;     // File system's disk device

kernel/syscall.c

@@ -104,6 +104,7 @@ extern uint64 sys_unlink(void);
 extern uint64 sys_wait(void);
 extern uint64 sys_write(void);
 extern uint64 sys_uptime(void);
+extern uint64 sys_symlink(void);
 
 static uint64 (*syscalls[])(void) = {
 [SYS_fork]    sys_fork,
@@ -127,6 +128,7 @@ static uint64 (*syscalls[])(void) = {
 [SYS_link]    sys_link,
 [SYS_mkdir]   sys_mkdir,
 [SYS_close]   sys_close,
+[SYS_symlink] sys_symlink,
 };
 
 void

kernel/syscall.h

@@ -1,22 +1,23 @@
 // System call numbers
-#define SYS_fork    1
-#define SYS_exit    2
-#define SYS_wait    3
-#define SYS_pipe    4
-#define SYS_read    5
-#define SYS_kill    6
-#define SYS_exec    7
-#define SYS_fstat   8
-#define SYS_chdir   9
-#define SYS_dup    10
-#define SYS_getpid 11
-#define SYS_sbrk   12
-#define SYS_sleep  13
-#define SYS_uptime 14
-#define SYS_open   15
-#define SYS_write  16
-#define SYS_mknod  17
-#define SYS_unlink 18
-#define SYS_link   19
-#define SYS_mkdir  20
-#define SYS_close  21
+#define SYS_fork     1
+#define SYS_exit     2
+#define SYS_wait     3
+#define SYS_pipe     4
+#define SYS_read     5
+#define SYS_kill     6
+#define SYS_exec     7
+#define SYS_fstat    8
+#define SYS_chdir    9
+#define SYS_dup     10
+#define SYS_getpid  11
+#define SYS_sbrk    12
+#define SYS_sleep   13
+#define SYS_uptime  14
+#define SYS_open    15
+#define SYS_write   16
+#define SYS_mknod   17
+#define SYS_unlink  18
+#define SYS_link    19
+#define SYS_mkdir   20
+#define SYS_close   21
+#define SYS_symlink 22

kernel/sysfile.c

@@ -286,7 +286,7 @@ create(char *path, short type, short major, short minor)
 uint64
 sys_open(void)
 {
-  char path[MAXPATH];
+  char path[MAXPATH], symlink_path[MAXPATH];
   int fd, omode;
   struct file *f;
   struct inode *ip;
@@ -322,6 +322,21 @@ sys_open(void)
     return -1;
   }
 
+  // Follow the symlinks 
+  if((ip->type == T_SYMLINK) && ((omode & O_NOFOLLOW) == 0)) {
+    safestrcpy(symlink_path, ip->path, sizeof(ip->path));
+    while(ip->type == T_SYMLINK) {
+      iunlock(ip);
+      // If symlinks form a cycle, return -1
+      if(((ip = namei(symlink_path)) == 0) || (!strncmp(symlink_path, path, MAXPATH))) { 
+        end_op();
+        return -1;
+      }
+      ilock(ip);
+      safestrcpy(symlink_path, ip->path, sizeof(ip->path));
+    }    
+  }
+
   if((f = filealloc()) == 0 || (fd = fdalloc(f)) < 0){
     if(f)
       fileclose(f);
@@ -484,3 +499,27 @@ sys_pipe(void)
   }
   return 0;
 }
+
+//int symlink(char *target, char *path);
+uint64 sys_symlink(void) {
+  char target[MAXPATH], path[MAXPATH];
+  struct inode *ip;
+
+  if(argstr(0, target, MAXPATH) < 0 || argstr(1, path, MAXPATH) < 0) 
+    return -1;
+  begin_op();
+
+  // Create new symlink file
+  if((ip = create(path, T_SYMLINK, 0, 0)) == 0) {
+    end_op();
+    return -1;
+  }
+
+  safestrcpy(ip->path, target, MAXPATH);
+
+  iupdate(ip);
+  iunlockput(ip);
+
+  end_op();
+  return 0;
+}

user/init.c

@@ -5,9 +5,9 @@
 #include "kernel/spinlock.h"
 #include "kernel/sleeplock.h"
 #include "kernel/fs.h"
-#include "kernel/file.h"
 #include "user/user.h"
 #include "kernel/fcntl.h"
+#include "kernel/file.h"
 
 char *argv[] = { "sh", 0 };
 

user/user.h

@@ -23,6 +23,7 @@ int getpid(void);
 char* sbrk(int);
 int sleep(int);
 int uptime(void);
+int symlink(char *target, char *path);
 
 // ulib.c
 int stat(const char*, struct stat*);

user/usys.pl

@@ -36,3 +36,4 @@ sub entry {
 entry("sbrk");
 entry("sleep");
 entry("uptime");
+entry("symlink");