dissect: refuse to use diskseq if ID_IGNORE_DISKSEQ=1 is specified

Follow-up for 1a81ddef00.

src/shared/dissect-image.c

@@ -32,6 +32,7 @@
 #include "copy.h"
 #include "cryptsetup-util.h"
 #include "device-nodes.h"
+#include "device-private.h"
 #include "device-util.h"
 #include "devnum-util.h"
 #include "discover-image.h"
@@ -516,6 +517,38 @@ static void dissected_partition_done(DissectedPartition *p) {
 }
 
 #if HAVE_BLKID
+static int diskseq_should_be_used(
+                const char *whole_devname,
+                uint64_t diskseq,
+                DissectImageFlags flags) {
+
+        int r;
+
+        assert(whole_devname);
+
+        /* No diskseq. We cannot use by-diskseq symlink. */
+        if (diskseq == 0)
+                return false;
+
+        /* Do not use by-diskseq link unless DISSECT_IMAGE_DISKSEQ_DEVNODE flag is explicitly set. */
+        if (!FLAGS_SET(flags, DISSECT_IMAGE_DISKSEQ_DEVNODE))
+                return false;
+
+        _cleanup_(sd_device_unrefp) sd_device *dev = NULL;
+        r = sd_device_new_from_devname(&dev, whole_devname);
+        if (r < 0)
+                return r;
+
+        /* When ID_IGNORE_DISKSEQ udev property is set, the by-diskseq symlink will not be created. */
+        r = device_get_property_bool(dev, "ID_IGNORE_DISKSEQ");
+        if (r >= 0)
+                return !r; /* If explicitly specified, use it. */
+        if (r != -ENOENT)
+                return r;
+
+        return true;
+}
+
 static int make_partition_devname(
                 const char *whole_devname,
                 uint64_t diskseq,
@@ -530,8 +563,10 @@ static int make_partition_devname(
         assert(nr != 0); /* zero is not a valid partition nr */
         assert(ret);
 
-        if (!FLAGS_SET(flags, DISSECT_IMAGE_DISKSEQ_DEVNODE) || diskseq == 0) {
-
+        r = diskseq_should_be_used(whole_devname, diskseq, flags);
+        if (r < 0)
+                log_debug_errno(r, "Failed to determine if diskseq should be used for %s, assuming no, ignoring: %m", whole_devname);
+        if (r <= 0) {
                 /* Given a whole block device node name (e.g. /dev/sda or /dev/loop7) generate a partition
                  * device name (e.g. /dev/sda7 or /dev/loop7p5). The rule the kernel uses is simple: if whole
                  * block device node name ends in a digit, then suffix a 'p', followed by the partition