Symbolic link implementation (in symlinks branch).

9e698c58 · rsc · f8ac6396 · 9e698c58 · 9e698c58 · 9e698c58
--- a/Makefile
+++ b/Makefile
@@ -98,11 +98,15 @@ _rm : rm.o $(ULIB)
 	$(LD) -N -e main -Ttext 0 -o _rm rm.o $(ULIB)
 	$(OBJDUMP) -S _rm > rm.asm
+_ln : ln.o $(ULIB)
+	$(LD) -N -e main -Ttext 0 -o _ln ln.o $(ULIB)
+	$(OBJDUMP) -S _ln > ln.asm
 mkfs : mkfs.c fs.h
 	cc -o mkfs mkfs.c
-fs.img : mkfs usertests _echo _cat README _init _sh _ls _mkdir _rm 
+fs.img : mkfs usertests _echo _cat README _init _sh _ls _mkdir _rm _ln
-	./mkfs fs.img usertests _echo _cat README _init _sh _ls _mkdir _rm
+	./mkfs fs.img usertests _echo _cat README _init _sh _ls _mkdir _rm _ln
 -include *.d

--- a/defs.h
+++ b/defs.h
@@ -135,6 +135,7 @@ int readi(struct inode*, char*, uint, uint);
 int writei(struct inode*, char*, uint, uint);
 struct inode* mknod(char*, short, short, short);
 struct inode* mknod1(struct inode*, char*, short, short, short);
+int symlink(char*, char*);
 int unlink(char*);
 void iupdate(struct inode*);
 int link(char*, char*);
--- a/fs.c
+++ b/fs.c
@@ -442,7 +442,7 @@ writei(struct inode *ip, char *addr, uint off, uint n)
    if(ip->major < 0 || ip->major >= NDEV || !devsw[ip->major].write)
      return -1;
    return devsw[ip->major].write(ip->minor, addr, n);
-  } else if(ip->type == T_FILE || ip->type == T_DIR) {
+  } else if(ip->type == T_FILE || ip->type == T_DIR || ip->type == T_SYMLINK) {
    struct buf *bp;
    int r = 0;
    int m;
@@ -493,14 +493,16 @@ namei(char *path, int mode, uint *ret_off,
      char **ret_last, struct inode **ret_ip)
 {
  struct inode *dp;
+  char link[64];
  struct proc *p = curproc[cpu()];
-  char *cp = path, *cp1;
+  char *cp, *cp1;
  uint off, dev;
  struct buf *bp;
  struct dirent *ep;
-  int i, l, atend;
+  int i, l, atend, n, nlink;
  uint ninum;
+again:
  if(ret_off)
    *ret_off = 0xffffffff;
  if(ret_last)
@@ -508,6 +510,7 @@ namei(char *path, int mode, uint *ret_off,
  if(ret_ip)
    *ret_ip = 0;
+  cp = path;
  if(*cp == '/')
    dp = iget(rootdev, 1);
  else {
@@ -516,13 +519,29 @@ namei(char *path, int mode, uint *ret_off,
    ilock(dp);
  }
+  nlink = 0;
  for(;;){
    while(*cp == '/')
      cp++;
    if(*cp == '\0'){
-      if(mode == NAMEI_LOOKUP)
+      if(mode == NAMEI_LOOKUP){
+        if(dp->type == T_SYMLINK){
+          if((n=readi(dp, link, 0, sizeof link - 1)) <= 0){
+            iput(dp);
+            return 0;
+          }
+          link[n] = 0;
+          path = link;
+          iput(dp);
+          if(++nlink > 10){
+            cprintf("symlink max depth: %s\n", path);
+            return 0;
+          }
+          goto again;
+        }
        return dp;
+      }
      if(mode == NAMEI_CREATE && ret_ip){
        *ret_ip = dp;
        return 0;
@@ -698,12 +717,12 @@ unlink(char *cp)
 // Create the path new as a link to the same inode as old.
 int
-link(char *name1, char *name2)
+link(char *old, char *new)
 {
  struct inode *ip, *dp;
  char *last;
-  if((ip = namei(name1, NAMEI_LOOKUP, 0, 0, 0)) == 0)
+  if((ip = namei(old, NAMEI_LOOKUP, 0, 0, 0)) == 0)
    return -1;
  if(ip->type == T_DIR){
    iput(ip);
@@ -712,7 +731,7 @@ link(char *name1, char *name2)
  iunlock(ip);
-  if((dp = namei(name2, NAMEI_CREATE, 0, &last, 0)) == 0) {
+  if((dp = namei(new, NAMEI_CREATE, 0, &last, 0)) == 0) {
    idecref(ip);
    return -1;
  }
@@ -732,3 +751,30 @@ link(char *name1, char *name2)
  return 0;
 }
+int
+strlen(char *s)
+{
+  int n = 0;
+  while(*s++ != 0)
+    n++;
+  return n;
+}
+// Create the path new as a symlink to old.
+int
+symlink(char *old, char *new)
+{
+  struct inode *ip, *dp;
+  char *last;
+  if((dp = namei(new, NAMEI_CREATE, 0, &last, 0)) == 0)
+    return -1;
+  ip = mknod1(dp, last, T_SYMLINK, 0, 0);
+  iput(dp);
+  if(ip == 0)
+    return -1;
+  writei(ip, old, 0, strlen(old));
+  iput(ip);
+  return 0;
+}
--- a/fs.h
+++ b/fs.h
@@ -33,6 +33,7 @@ struct dinode {
 #define T_DIR  1   // Directory
 #define T_FILE 2   // File
 #define T_DEV  3   // Special device
+#define T_SYMLINK 4   // Symbolic link
 // Inodes per block.
 #define IPB           (BSIZE / sizeof(struct dinode))

--- a/ln.c
+++ b/ln.c
+#include "types.h"
+#include "user.h"
+int
+main(int argc, char *argv[])
+{
+  int (*ln)(char*, char*);
+  ln = link;
+  if(argc > 1 && strcmp(argv[1], "-s") == 0){
+    ln = symlink;
+    argc--;
+    argv++;
+  }
+  if(argc != 3){
+    printf(2, "usage: ln [-s] old new (%d)\n", argc);
+    exit();
+  }
+  if(ln(argv[1], argv[2]) < 0){
+    printf(2, "%s failed\n", ln == symlink ? "symlink" : "link");
+    exit();
+  }
+  exit();
+}
--- a/rm.c
+++ b/rm.c
@@ -2,6 +2,7 @@
 #include "stat.h"
 #include "user.h"
+int
 main(int argc, char *argv[])
 {
  int i;

--- a/syscall.c
+++ b/syscall.c
@@ -104,6 +104,7 @@ extern int sys_open(void);
 extern int sys_pipe(void);
 extern int sys_read(void);
 extern int sys_sbrk(void);
+extern int sys_symlink(void);
 extern int sys_unlink(void);
 extern int sys_wait(void);
 extern int sys_write(void);
@@ -158,6 +159,9 @@ syscall(void)
  case SYS_link:
    ret = sys_link();
    break;
+  case SYS_symlink:
+    ret = sys_symlink();
+    break;
  case SYS_mkdir:
    ret = sys_mkdir();
    break;

--- a/syscall.h
+++ b/syscall.h
@@ -18,3 +18,4 @@
 #define SYS_dup    17
 #define SYS_getpid 18
 #define SYS_sbrk   19
+#define SYS_symlink 20
--- a/sysfile.c
+++ b/sysfile.c
@@ -313,6 +313,16 @@ sys_link(void)
 }
 int
+sys_symlink(void)
+{
+  char *old, *new;
+  if(argstr(0, &old) < 0 || argstr(1, &new) < 0)
+    return -1;
+  return symlink(old, new);
+}
+int
 sys_exec(void)
 {
  struct proc *cp = curproc[cpu()];

--- a/user.h
+++ b/user.h
@@ -11,8 +11,10 @@ int exec(char*, char**);
 int open(char*, int);
 int mknod(char*, short, short, short);
 int unlink(char*);
+struct stat;
 int fstat(int fd, struct stat*);
 int link(char*, char*);
+int symlink(char*, char*);
 int mkdir(char*);
 int chdir(char*);
 int dup(int);

--- a/usys.S
+++ b/usys.S
@@ -27,3 +27,4 @@ STUB(chdir)
 STUB(dup)
 STUB(getpid)
 STUB(sbrk)
+STUB(symlink)