lab fs/symlink: finishfs

8 files changed, 80 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index fd6e82e..8e50dfe 100644
--- a/Makefile
+++ b/Makefile
@@ -189,6 +189,7 @@ UPROGS=\
 	$U/_xargs\
 	$U/_trace\
 	$U/_sysinfotest\
+	$U/_symlinktest\
 
 
 
diff --git a/kernel/fcntl.h b/kernel/fcntl.h
index 44861b9..d7bb43b 100644
--- a/kernel/fcntl.h
+++ b/kernel/fcntl.h
@@ -1,5 +1,6 @@
 #define O_RDONLY  0x000
 #define O_WRONLY  0x001
 #define O_RDWR    0x002
+#define O_NOFOLLOW 0x010
 #define O_CREATE  0x200
 #define O_TRUNC   0x400
diff --git a/kernel/file.h b/kernel/file.h
index b993cc3..05d9377 100644
--- a/kernel/file.h
+++ b/kernel/file.h
@@ -46,3 +46,4 @@ extern struct devsw devsw[];
 
 #define CONSOLE 1
 #define STATS   2
+
diff --git a/kernel/stat.h b/kernel/stat.h
index 19543af..9554d30 100644
--- a/kernel/stat.h
+++ b/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
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 172c5ea..c39ebd8 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -119,6 +119,7 @@ extern uint64 sys_connect(void);
 #ifdef LAB_PGTBL
 extern uint64 sys_pgaccess(void);
 #endif
+extern uint64 sys_symlink(void);
 
 // An array mapping syscall numbers from syscall.h
 // to the function that handles the system call.
@@ -154,6 +155,7 @@ static uint64 (*syscalls[])(void) = {
 [SYS_sysinfo] sys_sysinfo,
 [SYS_sigalarm] sys_sigalarm,
 [SYS_sigreturn] sys_sigreturn,
+[SYS_symlink] sys_symlink,
 };
 
 // syscall name maps for SYS_trace:
@@ -189,6 +191,7 @@ static char *syscall_names[] = {
 [SYS_sysinfo] "sysinfo",
 [SYS_sigalarm]  "sigalarm",
 [SYS_sigreturn] "sigreturn",
+[SYS_symlink]  "symlink",
 };
 
 
diff --git a/kernel/sysfile.c b/kernel/sysfile.c
index 4b2189a..9c12d44 100644
--- a/kernel/sysfile.c
+++ b/kernel/sysfile.c
@@ -16,6 +16,15 @@
 #include "file.h"
 #include "fcntl.h"
 
+// symlink
+#define SYMLINK_MAXFOLLOW 254
+
+struct symlink {
+  uint len;
+  char target[MAXPATH];
+};
+
+
 // Fetch the nth word-sized system call argument as a file descriptor
 // and return both the descriptor and the corresponding struct file.
 static int
@@ -258,6 +267,8 @@ create(char *path, short type, short major, short minor)
     ilock(ip);
     if(type == T_FILE && (ip->type == T_FILE || ip->type == T_DEVICE))
       return ip;
+    if(type == T_SYMLINK)
+      return ip;
     iunlockput(ip);
     return 0;
   }
@@ -301,6 +312,37 @@ create(char *path, short type, short major, short minor)
   return 0;
 }
 
+// create a symbolic link to path
+uint64
+sys_symlink(void)
+{
+  char path[MAXPATH];
+  struct inode *ip;
+  struct symlink sl = {0};
+
+  if(argstr(0, sl.target, MAXPATH) < 0 || argstr(1, path, MAXPATH) < 0)
+    return -1;
+
+  sl.len = strlen(sl.target);
+
+  begin_op();
+  if((ip = create(path, T_SYMLINK, 0, 0)) == 0){
+    end_op();
+    return -1;
+  }
+
+  if(writei(ip, 0, (uint64)&sl.len, 0, sizeof(sl.len)) != sizeof(sl.len) || writei(ip, 0, (uint64)sl.target, sizeof(sl.len), sl.len+1) != sl.len+1){
+    iunlockput(ip);
+    end_op();
+    return -1;
+  }
+
+  iupdate(ip);
+  iunlockput(ip);
+  end_op();
+  return 0;
+}
+
 uint64
 sys_open(void)
 {
@@ -341,6 +383,35 @@ sys_open(void)
     return -1;
   }
 
+  if(ip->type == T_SYMLINK && !(omode & O_NOFOLLOW)){
+    int len = 0;
+    uchar i;
+    for(i = 0; i < SYMLINK_MAXFOLLOW; i++){
+      if(readi(ip, 0, (uint64)&len, 0, sizeof(len)) != sizeof(len) ||
+          readi(ip, 0, (uint64)path, sizeof(len), len+1) != len+1) {
+        iunlockput(ip);
+        end_op();
+        return -1;
+      }
+      iunlockput(ip);
+
+      if((ip = namei(path)) == 0) {
+        end_op();
+        return -1;
+      }
+
+      ilock(ip);
+      if(ip->type != T_SYMLINK)
+        break;
+    }
+
+    if (i >= SYMLINK_MAXFOLLOW) {
+      iunlockput(ip);
+      end_op();
+      return -1;
+    }
+  }
+
   if((f = filealloc()) == 0 || (fd = fdalloc(f)) < 0){
     if(f)
       fileclose(f);
diff --git a/user/user.h b/user/user.h
index 3544ac4..c1bccdd 100644
--- a/user/user.h
+++ b/user/user.h
@@ -39,6 +39,7 @@ int trace(int);
 int sysinfo(struct sysinfo*);
 int sigalarm(int ticks, void (*handler)());
 int sigreturn(void);
+int symlink(char *, char *);
 
 // ulib.c
 int stat(const char*, struct stat*);
diff --git a/user/usys.pl b/user/usys.pl
index 33af0ad..7f07795 100755
--- a/user/usys.pl
+++ b/user/usys.pl
@@ -42,3 +42,4 @@ entry("connect");
 entry("pgaccess");
 entry("sigalarm");
 entry("sigreturn");
+entry("symlink");