1 files changed, 123 insertions, 17 deletions

diff --git a/src/shared/util.c b/src/shared/util.c
index 857bb1b726..884e782c4f 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -62,6 +62,7 @@
 #include <sys/xattr.h>
 #include <libgen.h>
 #include <sys/statvfs.h>
+#include <sys/file.h>
 #include <linux/fs.h>
 #undef basename
 
@@ -4303,23 +4304,6 @@ bool machine_name_is_valid(const char *s) {
         return true;
 }
 
-bool image_name_is_valid(const char *s) {
-        if (!filename_is_valid(s))
-                return false;
-
-        if (string_has_cc(s, NULL))
-                return false;
-
-        if (!utf8_is_valid(s))
-                return false;
-
-        /* Temporary files for atomically creating new files */
-        if (startswith(s, ".#"))
-                return false;
-
-        return true;
-}
-
 int pipe_eof(int fd) {
         struct pollfd pollfd = {
                 .fd = fd,
@@ -7819,3 +7803,125 @@ int read_attr_path(const char *p, unsigned *ret) {
 
         return read_attr_fd(fd, ret);
 }
+
+int make_lock_file(const char *p, int operation, LockFile *ret) {
+        _cleanup_close_ int fd = -1;
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        /*
+         * We use UNPOSIX locks if they are available. They have nice
+         * semantics, and are mostly compatible with NFS. However,
+         * they are only available on new kernels. When we detect we
+         * are running on an older kernel, then we fall back to good
+         * old BSD locks. They also have nice semantics, but are
+         * slightly problematic on NFS, where they are upgraded to
+         * POSIX locks, even though locally they are orthogonal to
+         * POSIX locks.
+         */
+
+        t = strdup(p);
+        if (!t)
+                return -ENOMEM;
+
+        for (;;) {
+                struct flock fl = {
+                        .l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK,
+                        .l_whence = SEEK_SET,
+                };
+                struct stat st;
+
+                fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600);
+                if (fd < 0)
+                        return -errno;
+
+                r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl);
+                if (r < 0) {
+
+                        /* If the kernel is too old, use good old BSD locks */
+                        if (errno == EINVAL)
+                                r = flock(fd, operation);
+
+                        if (r < 0)
+                                return errno == EAGAIN ? -EBUSY : -errno;
+                }
+
+                /* If we acquired the lock, let's check if the file
+                 * still exists in the file system. If not, then the
+                 * previous exclusive owner removed it and then closed
+                 * it. In such a case our acquired lock is worthless,
+                 * hence try again. */
+
+                r = fstat(fd, &st);
+                if (r < 0)
+                        return -errno;
+                if (st.st_nlink > 0)
+                        break;
+
+                fd = safe_close(fd);
+        }
+
+        ret->path = t;
+        ret->fd = fd;
+        ret->operation = operation;
+
+        fd = -1;
+        t = NULL;
+
+        return r;
+}
+
+int make_lock_file_for(const char *p, int operation, LockFile *ret) {
+        const char *fn;
+        char *t;
+
+        assert(p);
+        assert(ret);
+
+        fn = basename(p);
+        if (!filename_is_valid(fn))
+                return -EINVAL;
+
+        t = newa(char, strlen(p) + 2 + 4 + 1);
+        stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck");
+
+        return make_lock_file(t, operation, ret);
+}
+
+void release_lock_file(LockFile *f) {
+        int r;
+
+        if (!f)
+                return;
+
+        if (f->path) {
+
+                /* If we are the exclusive owner we can safely delete
+                 * the lock file itself. If we are not the exclusive
+                 * owner, we can try becoming it. */
+
+                if (f->fd >= 0 &&
+                    (f->operation & ~LOCK_NB) == LOCK_SH) {
+                        static const struct flock fl = {
+                                .l_type = F_WRLCK,
+                                .l_whence = SEEK_SET,
+                        };
+
+                        r = fcntl(f->fd, F_OFD_SETLK, &fl);
+                        if (r < 0 && errno == EINVAL)
+                                r = flock(f->fd, LOCK_EX|LOCK_NB);
+
+                        if (r >= 0)
+                                f->operation = LOCK_EX|LOCK_NB;
+                }
+
+                if ((f->operation & ~LOCK_NB) == LOCK_EX)
+                        unlink_noerrno(f->path);
+
+                free(f->path);
+                f->path = NULL;
+        }
+
+        f->fd = safe_close(f->fd);
+        f->operation = 0;
+}