Create non-transferred files in a more atomic manner:

[rsync/rsync.git] / receiver.c

diff --git a/receiver.c b/receiver.c
index 9d839fa..965bb39 100644 (file)
--- a/receiver.c
+++ b/receiver.c
@@ -64,31 +64,36 @@ static flist_ndx_list batch_redo_list;
 /* We're either updating the basis file or an identical copy: */
 static int updating_basis_or_equiv;
 
-/*
- * get_tmpname() - create a tmp filename for a given filename
+#define TMPNAME_SUFFIX ".XXXXXX"
+#define TMPNAME_SUFFIX_LEN ((int)sizeof TMPNAME_SUFFIX - 1)
+#define MAX_UNIQUE_NUMBER 999999
+#define MAX_UNIQUE_LOOP 100
+
+/* get_tmpname() - create a tmp filename for a given filename
  *
- *   If a tmpdir is defined, use that as the directory to
- *   put it in.  Otherwise, the tmp filename is in the same
- *   directory as the given name.  Note that there may be no
- *   directory at all in the given name!
+ * If a tmpdir is defined, use that as the directory to put it in.  Otherwise,
+ * the tmp filename is in the same directory as the given name.  Note that
+ * there may be no directory at all in the given name!
  *
- *   The tmp filename is basically the given filename with a
- *   dot prepended, and .XXXXXX appended (for mkstemp() to
- *   put its unique gunk in).  Take care to not exceed
- *   either the MAXPATHLEN or NAME_MAX, esp. the last, as
- *   the basename basically becomes 8 chars longer. In that
- *   case, the original name is shortened sufficiently to
- *   make it all fit.
+ * The tmp filename is basically the given filename with a dot prepended, and
+ * .XXXXXX appended (for mkstemp() to put its unique gunk in).  We take care
+ * to not exceed either the MAXPATHLEN or NAME_MAX, especially the last, as
+ * the basename basically becomes 8 characters longer.  In such a case, the
+ * original name is shortened sufficiently to make it all fit.
  *
- *   Of course, there's no real reason for the tmp name to
- *   look like the original, except to satisfy us humans.
- *   As long as it's unique, rsync will work.
- */
-
-int get_tmpname(char *fnametmp, const char *fname)
+ * If the make_unique arg is True, the XXXXXX string is replaced with a unique
+ * string that doesn't exist at the time of the check.  This is intended to be
+ * used for creating hard links, symlinks, devices, and special files, since
+ * normal files should be handled by mkstemp() for safety.
+ *
+ * Of course, the only reason the file is based on the original name is to
+ * make it easier to figure out what purpose a temp file is serving when a
+ * transfer is in progress. */
+int get_tmpname(char *fnametmp, const char *fname, BOOL make_unique)
 {
        int maxname, added, length = 0;
        const char *f;
+       char *suf;
 
        if (tmpdir) {
                /* Note: this can't overflow, so the return value is safe */
@@ -108,8 +113,9 @@ int get_tmpname(char *fnametmp, const char *fname)
        fnametmp[length++] = '.';
 
        /* The maxname value is bufsize, and includes space for the '\0'.
-        * (Note that NAME_MAX get -8 for the leading '.' above.) */
-       maxname = MIN(MAXPATHLEN - 7 - length, NAME_MAX - 8);
+        * NAME_MAX needs an extra -1 for the name's leading dot. */
+       maxname = MIN(MAXPATHLEN - length - TMPNAME_SUFFIX_LEN,
+                     NAME_MAX - 1 - TMPNAME_SUFFIX_LEN);
 
        if (maxname < 1) {
                rprintf(FERROR_XFER, "temporary filename too long: %s\n", fname);
@@ -120,7 +126,33 @@ int get_tmpname(char *fnametmp, const char *fname)
        added = strlcpy(fnametmp + length, f, maxname);
        if (added >= maxname)
                added = maxname - 1;
-       memcpy(fnametmp + length + added, ".XXXXXX", 8);
+       suf = fnametmp + length + added;
+
+       if (make_unique) {
+               static unsigned counter_limit;
+               unsigned counter;
+
+               if (!counter_limit) {
+                       counter_limit = (unsigned)getpid() + MAX_UNIQUE_LOOP;
+                       if (counter_limit > MAX_UNIQUE_NUMBER || counter_limit < MAX_UNIQUE_LOOP)
+                               counter_limit = MAX_UNIQUE_LOOP;
+               }
+               counter = counter_limit - MAX_UNIQUE_LOOP;
+
+               /* This doesn't have to be very good because we don't need
+                * to worry about someone trying to guess the values:  all
+                * a conflict will do is cause a device, special file, hard
+                * link, or symlink to fail to be created.  Also: avoid
+                * using mktemp() due to gcc's annoying warning. */
+               while (1) {
+                       snprintf(suf, TMPNAME_SUFFIX_LEN+1, ".%d", counter);
+                       if (access(fnametmp, 0) < 0)
+                               break;
+                       if (++counter >= counter_limit)
+                               return 0;
+               }
+       } else
+               memcpy(suf, TMPNAME_SUFFIX, TMPNAME_SUFFIX_LEN+1);
 
        return 1;
 }
@@ -133,7 +165,7 @@ int open_tmpfile(char *fnametmp, const char *fname, struct file_struct *file)
 {
        int fd;
 
-       if (!get_tmpname(fnametmp, fname))
+       if (!get_tmpname(fnametmp, fname, False))
                return -1;
 
        /* We initially set the perms without the setuid/setgid bits or group
@@ -149,7 +181,7 @@ int open_tmpfile(char *fnametmp, const char *fname, struct file_struct *file)
        if (fd == -1 && relative_paths && errno == ENOENT
         && make_path(fnametmp, MKP_SKIP_SLASH | MKP_DROP_NAME) == 0) {
                /* Get back to name with XXXXXX in it. */
-               get_tmpname(fnametmp, fname);
+               get_tmpname(fnametmp, fname, False);
                fd = do_mkstemp(fnametmp, file->mode & INITACCESSPERMS);
        }
 #endif