add reflink support

Add option --reflink to deduplicate identical files via filesystem reflinks.
Reflink is done via the FICLONE ioctl, and allows to share the file
content across multiple inodes. This is similar to hardlink, with two
substantial differences:
- each copy has its own metadata (permissions, timestamps, attributes, etc.)
- on write, the content is copied (CoW) so the changes are not reflected to all other copies

Currently implemented only on Linux, it works with BtrFS and XFS (and ZFS to some extents)

fdupes.1

@@ -95,6 +95,11 @@ Prompt user for files to preserve, deleting all others (see
 .B CAVEATS
 below).
 .TP
+.B -e --reflink
+Linux only, attempt to reflink files to preserve space.
+Files must be on the same filesystem and the filesystem must support reflinking.
+Currently only BtrFS and XFS (and sometimes ZFS) support this feature.
+.TP
 .B -D --deferconfirmation
 In interactive mode, defer byte-for-byte confirmation of
 duplicates until just before file deletion.

fdupes.c

@@ -29,6 +29,16 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <time.h>
+#ifdef __linux__
+# include <linux/fs.h>
+# include <fcntl.h>
+# ifdef FICLONE
+#  define OPT_E "e"
+#  include <sys/ioctl.h>
+# else
+#  define OPT_E
+# endif
+#endif
 #ifdef HAVE_GETOPT_H
 #include <getopt.h>
 #endif
@@ -1191,6 +1201,49 @@ void deletefiles(file_t *files, int prompt, FILE *tty, char *logfile)
   free(preservestr);
 }
 
+void reflinkfile(file_t *existing, file_t *duplicate)
+{
+#ifdef FICLONE
+  int fd1, fd2, ret;
+
+  if (existing->device != duplicate->device)
+  {
+    fprintf(stderr, "error: %s and %s are not on the same device\n", existing->d_name, duplicate->d_name);
+    return;
+  }
+
+  fd1 = open(existing->d_name, O_RDONLY);
+  if (fd1 == -1)
+  {
+    printf("error opening %s\n", existing->d_name);
+    return;
+  }
+
+  fd2 = open(duplicate->d_name, O_WRONLY);
+  if (fd2 == -1)
+  {
+    printf("error opening %s\n", duplicate->d_name);
+    close(fd1);
+    return;
+  }
+
+  ret = ioctl(fd2, FICLONE, fd1);
+  if (ret == -1)
+    fprintf(stderr, "error reflinking %s to %s: %s\n", existing->d_name, duplicate->d_name, strerror(errno));
+
+  close(fd1);
+  close(fd2);
+#endif
+}
+
+void reflinkfiles(file_t *files)
+{
+  file_t *first = files;
+
+  for (files = first; files->next; files = files->next)
+    reflinkfile(first, files->next);
+}
+
 int sort_pairs_by_arrival(file_t *f1, file_t *f2)
 {
   if (f2->duplicates != 0)
@@ -1401,6 +1454,7 @@ void help_text()
   printf("                         with -s or --symlinks, or when specifying a\n");
   printf("                         particular directory more than once; refer to the\n");
   printf("                         fdupes documentation for additional information\n");
+  printf(" -e --relink             reflink files to the first file in each set\n");
   printf(" -D --deferconfirmation  in interactive mode, defer byte-for-byte confirmation\n");
   printf("                         of duplicates until just before file deletion\n");
 #ifndef NO_NCURSES
@@ -1503,6 +1557,9 @@ int main(int argc, char **argv) {
     { "log", 1, 0, 'l' },
     { "deferconfirmation", 0, 0, 'D' },
     { "cache", 0, 0, 'c' },
+#ifdef FICLONE
+    { "reflink", 0, 0, 'e' },
+#endif
     { 0, 0, 0, 0 }
   };
 #define GETOPT getopt_long
@@ -1516,7 +1573,7 @@ int main(int argc, char **argv) {
 
   oldargv = cloneargs(argc, argv);
 
-  while ((opt = GETOPT(argc, argv, "frRq1StsHG:L:nAdPvhNImpo:il:Dcx:"
+  while ((opt = GETOPT(argc, argv, "frRq1StsHG:L:nAdPvhNImpo:il:Dcx:" OPT_E
 #ifdef HAVE_GETOPT_H
           , long_options, NULL
 #endif
@@ -1574,6 +1631,9 @@ int main(int argc, char **argv) {
     case 'd':
       SETFLAG(flags, F_DELETEFILES);
       break;
+    case 'e':
+      SETFLAG(flags, F_REFLINK);
+      break;
     case 'P':
       SETFLAG(flags, F_PLAINPROMPT);
       break;
@@ -1675,8 +1735,8 @@ int main(int argc, char **argv) {
     exit(1);
   }
 
-  if (ISFLAG(flags, F_SUMMARIZEMATCHES) && ISFLAG(flags, F_DELETEFILES)) {
-    errormsg("options --summarize and --delete are not compatible\n");
+  if (ISFLAG(flags, F_SUMMARIZEMATCHES) && (ISFLAG(flags, F_DELETEFILES) || ISFLAG(flags, F_REFLINK))) {
+    errormsg("options --summarize is not compatible with --delete or --reflink\n");
     exit(1);
   }
 
@@ -1686,6 +1746,12 @@ int main(int argc, char **argv) {
     exit(1);
   }
 
+  if (ISFLAG(flags, F_DELETEFILES) && ISFLAG(flags, F_REFLINK))
+  {
+    errormsg("options --delete and --reflink are not compatible\n");
+    exit(1);
+  }
+
   if (!ISFLAG(flags, F_DELETEFILES)) {
     logfile = 0;
     loginfo = 0;
@@ -1842,6 +1908,8 @@ int main(int argc, char **argv) {
               ordertype == ORDER_CTIME ? sort_pairs_by_ctime :
                                          sort_pairs_by_filename, loginfo );
       }
+      else if (ISFLAG(flags, F_REFLINK) && ISFLAG(flags, F_IMMEDIATE))
+          reflinkfile(*match, curfile);
       else if (ISFLAG(flags, F_DEFERCONFIRMATION) || confirmmatch(file1, file2))
         registerpair(match, curfile,
             ordertype == ORDER_MTIME ? sort_pairs_by_mtime :
@@ -1918,6 +1986,12 @@ int main(int argc, char **argv) {
     }
   }
 
+  else if (ISFLAG(flags, F_REFLINK))
+  {
+    if (ISFLAG(flags, F_NOPROMPT) || ISFLAG(flags, F_IMMEDIATE))
+      reflinkfiles(files);
+  }
+
   else 
 
     if (ISFLAG(flags, F_SUMMARIZEMATCHES))

flags.h

@@ -28,6 +28,7 @@
 #define F_PRUNECACHE        0x200000
 #define F_READONLYCACHE     0x400000
 #define F_VACUUMCACHE       0x800000
+#define F_REFLINK           0x1000000
 
 extern unsigned long flags;