Implemented safe writing of config files

HISTORY

@@ -340,3 +340,5 @@ Video Disk Recorder Revision History
 - Changed the value for Diseqc to '0' in the default 'channels.conf'.
 - Fixed displaying channels and recording status in the RCU's LED display when
   a recording is interrupted due to higher priority.
+- Implemented safe writing of config files (first writes into a temporary file
+  and then renames it).

config.c

@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: config.c 1.37 2001/01/13 12:36:32 kls Exp $
+ * $Id: config.c 1.38 2001/01/13 15:36:31 kls Exp $
  */
 
 #include "config.h"
@@ -119,10 +119,9 @@ bool cKeys::Load(const char *FileName)
 
 bool cKeys::Save(void)
 {
-  //TODO make backup copies???
   bool result = true;
-  FILE *f = fopen(fileName, "w");
-  if (f) {
+  cSafeFile f(fileName);
+  if (f.Open()) {
      if (fprintf(f, "Code\t%c\nAddress\t%04X\n", code, address) > 0) {
         for (tKey *k = keys; k->type != kNone; k++) {
             if (fprintf(f, "%s\t%08X\n", k->name, k->code) <= 0) {
@@ -133,7 +132,7 @@ bool cKeys::Save(void)
          }
      else
         result = false;
-     fclose(f);
+     f.Close();
      }
   else
      result = false;
@@ -782,8 +781,8 @@ bool cSetup::Save(const char *FileName)
   if (!FileName)
      FileName = fileName;
   if (FileName) {
-     FILE *f = fopen(FileName, "w");
-     if (f) {
+     cSafeFile f(FileName);
+     if (f.Open()) {
         fprintf(f, "# VDR Setup\n");
         fprintf(f, "OSDLanguage        = %d\n", OSDLanguage);
         fprintf(f, "PrimaryDVB         = %d\n", PrimaryDVB);
@@ -796,7 +795,7 @@ bool cSetup::Save(const char *FileName)
         fprintf(f, "MarginStart        = %d\n", MarginStart);
         fprintf(f, "MarginStop         = %d\n", MarginStop);
         fprintf(f, "EPGScanTimeout     = %d\n", EPGScanTimeout);
-        fclose(f);
+        f.Close();
         isyslog(LOG_INFO, "saved setup to %s", FileName);
         return true;
         }

config.h

@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: config.h 1.36 2000/12/25 14:20:09 kls Exp $
+ * $Id: config.h 1.37 2001/01/13 14:56:29 kls Exp $
  */
 
 #ifndef __CONFIG_H
@@ -202,11 +202,10 @@ public:
   }
   bool Save(void)
   {
-  //TODO make backup copies???
     bool result = true;
     T *l = (T *)First();
-    FILE *f = fopen(fileName, "w");
-    if (f) {
+    cSafeFile f(fileName);
+    if (f.Open()) {
        while (l) {
              if (!l->Save(f)) {
                 result = false;
@@ -214,12 +213,10 @@ public:
                 }
              l = (T *)l->Next();
              }
-       fclose(f);
+       f.Close();
        }
-    else {
-       LOG_ERROR_STR(fileName);
+    else
        result = false;
-       }
     return result;
   }
   };

tools.c

@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: tools.c 1.26 2001/01/13 12:17:30 kls Exp $
+ * $Id: tools.c 1.27 2001/01/13 15:35:02 kls Exp $
  */
 
 #define _GNU_SOURCE
@@ -247,6 +247,27 @@ bool RemoveFileOrDir(const char *FileName, bool FollowSymlinks)
   return true;
 }
 
+char *ReadLink(const char *FileName)
+{
+  char RealName[_POSIX_PATH_MAX];
+  const char *TargetName = NULL;
+  int n = readlink(FileName, RealName, sizeof(RealName) - 1);
+  if (n < 0) {
+     if (errno == ENOENT || errno == EINVAL) // file doesn't exist or is not a symlink
+        TargetName = FileName;
+     else { // some other error occurred
+        LOG_ERROR_STR(FileName);
+        }
+     }
+  else if (n < int(sizeof(RealName))) { // got it!
+     RealName[n] = 0;
+     TargetName = RealName;
+     }
+  else
+     esyslog(LOG_ERR, "ERROR: symlink's target name too long: %s", FileName);
+  return TargetName ? strdup(TargetName) : NULL;
+}
+
 // --- cFile -----------------------------------------------------------------
 
 bool cFile::files[FD_SETSIZE] = { false };
@@ -367,6 +388,45 @@ bool cFile::FileReady(int FileDes, int TimeoutMs)
   return select(FD_SETSIZE, &set, NULL, NULL, &timeout) > 0 && FD_ISSET(FileDes, &set);
 }
 
+// --- cSafeFile -------------------------------------------------------------
+
+cSafeFile::cSafeFile(const char *FileName)
+{
+  f = NULL;
+  fileName = ReadLink(FileName);
+  tempName = fileName ? new char[strlen(fileName) + 5] : NULL;
+  if (tempName)
+     strcat(strcpy(tempName, fileName), ".$$$");
+}
+
+cSafeFile::~cSafeFile()
+{
+  if (f)
+     fclose(f);
+  unlink(tempName);
+  delete fileName;
+  delete tempName;
+}
+
+bool cSafeFile::Open(void)
+{
+  if (!f && fileName && tempName) {
+     f = fopen(tempName, "w");
+     if (!f)
+        LOG_ERROR_STR(tempName);
+     }
+  return f != NULL;
+}
+
+void cSafeFile::Close(void)
+{
+  if (f) {
+     fclose(f);
+     f = NULL;
+     rename(tempName, fileName);
+     }
+}
+
 // --- cListObject -----------------------------------------------------------
 
 cListObject::cListObject(void)

tools.h

@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: tools.h 1.22 2000/12/10 11:49:42 kls Exp $
+ * $Id: tools.h 1.23 2001/01/13 15:36:00 kls Exp $
  */
 
 #ifndef __TOOLS_H
@@ -48,6 +48,7 @@ uint FreeDiskSpaceMB(const char *Directory);
 bool DirectoryOk(const char *DirName, bool LogErrors = false);
 bool MakeDirs(const char *FileName, bool IsDirectory = false);
 bool RemoveFileOrDir(const char *FileName, bool FollowSymlinks = false);
+char *ReadLink(const char *FileName);
 
 class cFile {
 private:
@@ -68,6 +69,19 @@ public:
   static bool FileReady(int FileDes, int TimeoutMs = 1000);
   };
 
+class cSafeFile {
+private:
+  FILE *f;
+  char *fileName;
+  char *tempName;
+public:
+  cSafeFile(const char *FileName);
+  ~cSafeFile();
+  operator FILE* () { return f; }
+  bool Open(void);
+  void Close(void);
+  };
+
 class cListObject {
 private:
   cListObject *prev, *next;