util: add rename_noreplace

[elogind.git] / src / shared / util.c

diff --git a/src/shared/util.c b/src/shared/util.c
index a13819e79ac8acb5e21d71a9474412cee2b222a8..55de83023d53c1e6c34226e532df505418473561 100644 (file)
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -2592,7 +2592,7 @@ char* dirname_malloc(const char *path) {
 int dev_urandom(void *p, size_t n) {
         static int have_syscall = -1;
 
-        _cleanup_close_ fd = -1;
+        _cleanup_close_ int fd = -1;
         int r;
 
         /* Gathers some randomness from the kernel. This call will
@@ -8122,3 +8122,44 @@ void cmsg_close_all(struct msghdr *mh) {
                 if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS)
                         close_many((int*) CMSG_DATA(cmsg), (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int));
 }
+
+int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
+        struct stat buf;
+        int ret;
+
+        ret = renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE);
+        if (ret >= 0)
+                return 0;
+
+        /* Even though renameat2() exists since Linux 3.15, btrfs added
+         * support for it later. If it is not implemented, fallback to another
+         * method. */
+        if (errno != EINVAL)
+                return -errno;
+
+        /* The link()/unlink() fallback does not work on directories. But
+         * renameat() without RENAME_NOREPLACE gives the same semantics on
+         * directories, except when newpath is an *empty* directory. This is
+         * good enough. */
+        ret = fstatat(olddirfd, oldpath, &buf, AT_SYMLINK_NOFOLLOW);
+        if (ret >= 0 && S_ISDIR(buf.st_mode)) {
+                ret = renameat(olddirfd, oldpath, newdirfd, newpath);
+                return ret >= 0 ? 0 : -errno;
+        }
+
+        /* If it is not a directory, use the link()/unlink() fallback. */
+        ret = linkat(olddirfd, oldpath, newdirfd, newpath, 0);
+        if (ret < 0)
+                return -errno;
+
+        ret = unlinkat(olddirfd, oldpath, 0);
+        if (ret < 0) {
+                /* backup errno before the following unlinkat() alters it */
+                ret = errno;
+                (void) unlinkat(newdirfd, newpath, 0);
+                errno = ret;
+                return -errno;
+        }
+
+        return 0;
+}