repart: Allow configuring sector size

Let's allow users to configure the (logical) sector size of their
image. This is required when building images for a 4k sector size
disk on a 512b sector size host or vice-versa.

src/basic/parse-util.c

@@ -256,6 +256,26 @@ int parse_size(const char *t, uint64_t base, uint64_t *size) {
         return 0;
 }
 
+int parse_sector_size(const char *t, uint64_t *ret) {
+        int r;
+
+        assert(t);
+        assert(ret);
+
+        uint64_t ss;
+
+        r = safe_atou64(t, &ss);
+        if (r < 0)
+                return log_error_errno(r, "Failed to parse sector size parameter %s", t);
+        if (ss < 512 || ss > 4096) /* Allow up to 4K due to dm-crypt support and 4K alignment by the homed LUKS backend */
+                return log_error_errno(SYNTHETIC_ERRNO(ERANGE), "Sector size not between 512 and 4096: %s", t);
+        if (!ISPOWEROF2(ss))
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Sector size not power of 2: %s", t);
+
+        *ret = ss;
+        return 0;
+}
+
 int parse_range(const char *t, unsigned *lower, unsigned *upper) {
         _cleanup_free_ char *word = NULL;
         unsigned l, u;

src/basic/parse-util.h

@@ -18,6 +18,7 @@ int parse_ifindex(const char *s);
 int parse_mtu(int family, const char *s, uint32_t *ret);
 
 int parse_size(const char *t, uint64_t base, uint64_t *size);
+int parse_sector_size(const char *t, uint64_t *ret);
 int parse_range(const char *t, unsigned *lower, unsigned *upper);
 int parse_errno(const char *t);