fstab-generator: properly deal with discard as non-last option

Previous code would only return correct results when discard
was the last option.

While at it, avoid incorrect behaviour for (invalid) 'pri' option
not followed by '=...', and also do not return -1 as the error code.

src/core/swap.c

@@ -610,7 +610,7 @@ static void swap_dump(Unit *u, FILE *f, const char *prefix) {
                         prefix, p->priority,
                         prefix, yes_no(p->noauto),
                         prefix, yes_no(p->nofail),
-                        prefix, p->discard);
+                        prefix, p->discard ?: "none");
 
         if (s->control_pid > 0)
                 fprintf(f,

src/fstab-generator/fstab-generator.c

@@ -46,34 +46,70 @@ static int arg_root_rw = -1;
 
 
 static int mount_find_pri(struct mntent *me, int *ret) {
-        char *end, *pri;
+        char *end, *opt;
         unsigned long r;
 
         assert(me);
         assert(ret);
 
-        pri = hasmntopt(me, "pri");
-        if (!pri)
+        opt = hasmntopt(me, "pri");
+        if (!opt)
                 return 0;
 
-        pri += 4;
+        opt += strlen("pri");
+
+        if (*opt != '=')
+                return -EINVAL;
 
         errno = 0;
-        r = strtoul(pri, &end, 10);
+        r = strtoul(opt + 1, &end, 10);
         if (errno > 0)
                 return -errno;
 
-        if (end == pri || (*end != ',' && *end != 0))
+        if (end == opt + 1 || (*end != ',' && *end != 0))
                 return -EINVAL;
 
         *ret = (int) r;
         return 1;
 }
 
+static int mount_find_discard(struct mntent *me, char **ret) {
+        char *opt, *ans;
+        size_t len;
+
+        assert(me);
+        assert(ret);
+
+        opt = hasmntopt(me, "discard");
+        if (!opt)
+                return 0;
+
+        opt += strlen("discard");
+
+        if (*opt == ',' || *opt == '\0')
+                ans = strdup("all");
+        else {
+                if (*opt != '=')
+                        return -EINVAL;
+
+                len = strcspn(opt + 1, ",");
+                if (len == 0)
+                        return -EINVAL;
+
+                ans = strndup(opt + 1, len);
+        }
+
+        if (!ans)
+                return -ENOMEM;
+
+        *ret = ans;
+        return 1;
+}
+
 static int add_swap(const char *what, struct mntent *me) {
         _cleanup_free_ char *name = NULL, *unit = NULL, *lnk = NULL;
         _cleanup_fclose_ FILE *f = NULL;
-        char *discard = NULL;
+        _cleanup_free_ char *discard = NULL;
 
         bool noauto;
         int r, pri = -1;
@@ -89,7 +125,13 @@ static int add_swap(const char *what, struct mntent *me) {
         r = mount_find_pri(me, &pri);
         if (r < 0) {
                 log_error("Failed to parse priority");
-                return pri;
+                return r;
+        }
+
+        r = mount_find_discard(me, &discard);
+        if (r < 0) {
+                log_error("Failed to parse discard");
+                return r;
         }
 
         noauto = !!hasmntopt(me, "noauto");
@@ -120,18 +162,11 @@ static int add_swap(const char *what, struct mntent *me) {
                 "What=%s\n",
                 what);
 
-        discard = mount_test_option(me->mnt_opts, "discard");
-        if (discard) {
-                discard = strpbrk(discard, "=");
-                fprintf(f,
-                        "Discard=%s\n",
-                        discard ? discard+1 : "all");
-        }
-
         if (pri >= 0)
-                fprintf(f,
-                        "Priority=%i\n",
-                        pri);
+                fprintf(f, "Priority=%i\n", pri);
+
+        if (discard)
+                fprintf(f, "Discard=%s\n", discard);
 
         fflush(f);
         if (ferror(f)) {