dissect: make using a generic partition as root partition optional

In preparation for reusing the image dissector in the GPT auto-discovery
logic, only optionally fail the dissection when we can't identify a root
partition.

In the GPT auto-discovery we are completely fine with any kind of root,
given that we run when it is already mounted and all we do is find some
additional auxiliary partitions on the same disk.

1 files changed, 17 insertions, 8 deletions

diff --git a/src/shared/dissect-image.c b/src/shared/dissect-image.c
index 5b6e78dd3d..878cb008aa 100644
--- a/src/shared/dissect-image.c
+++ b/src/shared/dissect-image.c
@@ -174,7 +174,8 @@ int dissect_image(int fd, const void *root_hash, size_t root_hash_size, DissectI
         if (!m)
                 return -ENOMEM;
 
-        if ((flags & DISSECT_IMAGE_GPT_ONLY) == 0) {
+        if (!(flags & DISSECT_IMAGE_GPT_ONLY) &&
+            (flags & DISSECT_IMAGE_REQUIRE_ROOT)) {
                 const char *usage = NULL;
 
                 (void) blkid_probe_lookup_value(b, "USAGE", &usage, NULL);
@@ -490,7 +491,7 @@ int dissect_image(int fd, const void *root_hash, size_t root_hash_size, DissectI
                  * either, then check if there's a single generic one, and use that. */
 
                 if (m->partitions[PARTITION_ROOT_VERITY].found)
-                        return -ENXIO;
+                        return -EADDRNOTAVAIL;
 
                 if (m->partitions[PARTITION_ROOT_SECONDARY].found) {
                         m->partitions[PARTITION_ROOT] = m->partitions[PARTITION_ROOT_SECONDARY];
@@ -499,8 +500,19 @@ int dissect_image(int fd, const void *root_hash, size_t root_hash_size, DissectI
                         m->partitions[PARTITION_ROOT_VERITY] = m->partitions[PARTITION_ROOT_SECONDARY_VERITY];
                         zero(m->partitions[PARTITION_ROOT_SECONDARY_VERITY]);
 
-                } else if (generic_node && !root_hash) {
+                } else if (flags & DISSECT_IMAGE_REQUIRE_ROOT) {
+
+                        /* If the root has was set, then we won't fallback to a generic node, because the root hash
+                         * decides */
+                        if (root_hash)
+                                return -EADDRNOTAVAIL;
 
+                        /* If we didn't find a generic node, then we can't fix this up either */
+                        if (!generic_node)
+                                return -ENXIO;
+
+                        /* If we didn't find a properly marked root partition, but we did find a single suitable
+                         * generic Linux partition, then use this as root partition, if the caller asked for it. */
                         if (multiple_generic)
                                 return -ENOTUNIQ;
 
@@ -514,14 +526,11 @@ int dissect_image(int fd, const void *root_hash, size_t root_hash_size, DissectI
                         };
 
                         generic_node = NULL;
-                } else
-                        return -ENXIO;
+                }
         }
 
-        assert(m->partitions[PARTITION_ROOT].found);
-
         if (root_hash) {
-                if (!m->partitions[PARTITION_ROOT_VERITY].found)
+                if (!m->partitions[PARTITION_ROOT_VERITY].found || !m->partitions[PARTITION_ROOT].found)
                         return -EADDRNOTAVAIL;
 
                 /* If we found the primary root with the hash, then we definitely want to suppress any secondary root