2 files changed, 87 insertions, 0 deletions

diff --git a/src/shared/mount-util.c b/src/shared/mount-util.c
index 8acbadcaf9..8ba054471f 100644
--- a/src/shared/mount-util.c
+++ b/src/shared/mount-util.c
@@ -1574,3 +1574,88 @@ int mount_credentials_fs(const char *path, size_t size, bool ro) {
                         credentials_fs_mount_flags(ro),
                         opts);
 }
+
+int make_fsmount(
+                int error_log_level,
+                const char *what,
+                const char *type,
+                unsigned long flags,
+                const char *options,
+                int userns_fd) {
+
+        _cleanup_close_ int fs_fd = -EBADF, mnt_fd = -EBADF;
+        _cleanup_free_ char *o = NULL;
+        unsigned long f;
+        int r;
+
+        assert(type);
+        assert(what);
+
+        r = mount_option_mangle(options, flags, &f, &o);
+        if (r < 0)
+                return log_full_errno(
+                                error_log_level, r, "Failed to mangle mount options %s: %m",
+                                strempty(options));
+
+        if (DEBUG_LOGGING) {
+                _cleanup_free_ char *fl = NULL;
+                (void) mount_flags_to_string(f, &fl);
+
+                log_debug("Creating mount fd for %s (%s) (%s \"%s\")...",
+                        strna(what), strna(type), strnull(fl), strempty(o));
+        }
+
+        fs_fd = fsopen(type, FSOPEN_CLOEXEC);
+        if (fs_fd < 0)
+                return log_full_errno(error_log_level, errno, "Failed to open superblock for \"%s\": %m", type);
+
+        if (fsconfig(fs_fd, FSCONFIG_SET_STRING, "source", what, 0) < 0)
+                return log_full_errno(error_log_level, errno, "Failed to set mount source for \"%s\" to \"%s\": %m", type, what);
+
+        if (FLAGS_SET(f, MS_RDONLY))
+                if (fsconfig(fs_fd, FSCONFIG_SET_FLAG, "ro", NULL, 0) < 0)
+                        return log_full_errno(error_log_level, errno, "Failed to set read only mount flag for \"%s\": %m", type);
+
+        for (const char *p = o;;) {
+                _cleanup_free_ char *word = NULL;
+                char *eq;
+
+                r = extract_first_word(&p, &word, ",", EXTRACT_KEEP_QUOTE);
+                if (r < 0)
+                        return log_full_errno(error_log_level, r, "Failed to parse mount option string \"%s\": %m", o);
+                if (r == 0)
+                        break;
+
+                eq = strchr(word, '=');
+                if (eq) {
+                        *eq = 0;
+                        eq++;
+
+                        if (fsconfig(fs_fd, FSCONFIG_SET_STRING, word, eq, 0) < 0)
+                                return log_full_errno(error_log_level, errno, "Failed to set mount option \"%s=%s\" for \"%s\": %m", word, eq, type);
+                } else {
+                        if (fsconfig(fs_fd, FSCONFIG_SET_FLAG, word, NULL, 0) < 0)
+                                return log_full_errno(error_log_level, errno, "Failed to set mount flag \"%s\" for \"%s\": %m", word, type);
+                }
+        }
+
+        if (fsconfig(fs_fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) < 0)
+                return log_full_errno(error_log_level, errno, "Failed to realize fs fd for \"%s\" (\"%s\"): %m", what, type);
+
+        mnt_fd = fsmount(fs_fd, FSMOUNT_CLOEXEC, 0);
+        if (mnt_fd < 0)
+                return log_full_errno(error_log_level, errno, "Failed to create mount fd for \"%s\" (\"%s\"): %m", what, type);
+
+        if (mount_setattr(mnt_fd, "", AT_EMPTY_PATH|AT_RECURSIVE,
+                          &(struct mount_attr) {
+                                  .attr_set = ms_flags_to_mount_attr(f) | (userns_fd >= 0 ? MOUNT_ATTR_IDMAP : 0),
+                                  .userns_fd = userns_fd,
+                          }, MOUNT_ATTR_SIZE_VER0) < 0)
+                return log_full_errno(error_log_level,
+                                      errno,
+                                      "Failed to set mount flags for \"%s\" (\"%s\"): %m",
+                                      what,
+                                      type);
+
+        return TAKE_FD(mnt_fd);
+}
diff --git a/src/shared/mount-util.h b/src/shared/mount-util.h
index fb496e156b..a56530c42e 100644
--- a/src/shared/mount-util.h
+++ b/src/shared/mount-util.h
@@ -136,3 +136,5 @@ int trigger_automount_at(int dir_fd, const char *path);
 
 unsigned long credentials_fs_mount_flags(bool ro);
 int mount_credentials_fs(const char *path, size_t size, bool ro);
+
+int make_fsmount(int error_log_level, const char *what, const char *type, unsigned long flags, const char *options, int userns_fd);