shared/blockdev-list: add flag to gather diskseq stats

Only one caller ever looks at this field. Let's optimize a bit.

src/repart/repart-list-candidate-devices.c

@@ -161,8 +161,9 @@ int vl_method_list_candidate_devices(
                 BLOCKDEV_LIST_SHOW_SYMLINKS|
                 BLOCKDEV_LIST_REQUIRE_PARTITION_SCANNING|
                 BLOCKDEV_LIST_IGNORE_ZRAM|
-                BLOCKDEV_LIST_METADATA|
                 BLOCKDEV_LIST_IGNORE_READ_ONLY|
+                BLOCKDEV_LIST_METADATA|
+                BLOCKDEV_LIST_DISKSEQ|
                 (p.ignore_empty ? BLOCKDEV_LIST_IGNORE_EMPTY : 0)|
                 (p.ignore_root ? BLOCKDEV_LIST_IGNORE_ROOT : 0);
 

src/shared/blockdev-list.c

@@ -279,9 +279,11 @@ int blockdev_list_one(
                 }
 
                 uint64_t diskseq = UINT64_MAX;
-                r = sd_device_get_diskseq(dev, &diskseq);
-                if (r < 0)
-                        log_device_debug_errno(dev, r, "Failed to acquire diskseq of device '%s', ignoring: %m", node);
+                if (FLAGS_SET(flags, BLOCKDEV_LIST_DISKSEQ)) {
+                        r = sd_device_get_diskseq(dev, &diskseq);
+                        if (r < 0)
+                                log_device_debug_errno(dev, r, "Failed to acquire diskseq of device '%s', ignoring: %m", node);
+                }
 
                 _cleanup_free_ char *m = strdup(node);
                 if (!m)

src/shared/blockdev-list.h

@@ -14,6 +14,7 @@ typedef enum BlockDevListFlags {
         BLOCKDEV_LIST_IGNORE_READ_ONLY           = 1 << 7,  /* Ignore read-only block devices */
         BLOCKDEV_LIST_REQUIRE_LUKS               = 1 << 8,  /* Only consider block devices with LUKS superblocks */
         BLOCKDEV_LIST_METADATA                   = 1 << 9,  /* Fill in model, vendor, subsystem, read_only */
+        BLOCKDEV_LIST_DISKSEQ                    = 1 << 10, /* Fill in the diskseq field */
 } BlockDevListFlags;
 
 /* The "dynamic" filters – ones the kernel can flip at runtime via sysattrs on a live device.