Add atomic_symlink(), prepare for 2.6.3.0

1 files changed, 41 insertions, 0 deletions

diff --git a/src/libunixonacid/atomic_symlink.c b/src/libunixonacid/atomic_symlink.c
new file mode 100644
index 0000000..660e4d3
--- /dev/null
+++ b/src/libunixonacid/atomic_symlink.c
@@ -0,0 +1,41 @@
+/* ISC license. */
+
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <skalibs/random.h>
+#include <skalibs/unix-transactional.h>
+
+int atomic_symlink (char const *target, char const *name, char const *suffix)
+{
+  {
+    int e = errno ;
+    if (symlink(target, name) == 0) return 1 ;
+    if (errno != EEXIST) return 0 ;
+    errno = e ;
+  }
+  {
+    size_t namelen = strlen(name) ;
+    size_t suffixlen = suffix ? strlen(suffix) : 8 ;
+    char tmp[namelen + suffixlen + 2] ;
+    memcpy(tmp, name, namelen) ;
+    tmp[namelen] = ':' ;
+    if (suffix)
+      memcpy(tmp + namelen + 1, suffix, suffixlen + 1) ;
+    else
+    {
+      random_name(tmp + namelen + 1, 8) ;
+      tmp[namelen + 9] = 0 ;
+    }
+    if (symlink(target, tmp) < 0) return 0 ;
+    if (rename(tmp, name) < 0)
+    {
+      int e = errno ;
+      unlink(tmp) ;
+      errno = e ;
+      return 0 ;
+    }
+  }
+  return 1 ;
+}