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.

6 files changed, 27 insertions, 13 deletions

diff --git a/src/dissect/dissect.c b/src/dissect/dissect.c
index 78ec88fa35..fd9db5ba87 100644
--- a/src/dissect/dissect.c
+++ b/src/dissect/dissect.c
@@ -35,7 +35,7 @@ static enum {
 } arg_action = ACTION_DISSECT;
 static const char *arg_image = NULL;
 static const char *arg_path = NULL;
-static DissectImageFlags arg_flags = DISSECT_IMAGE_DISCARD_ON_LOOP;
+static DissectImageFlags arg_flags = DISSECT_IMAGE_REQUIRE_ROOT|DISSECT_IMAGE_DISCARD_ON_LOOP;
 static void *arg_root_hash = NULL;
 static size_t arg_root_hash_size = 0;
 
@@ -191,7 +191,7 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
-        r = dissect_image(d->fd, arg_root_hash, arg_root_hash_size, 0, &m);
+        r = dissect_image(d->fd, arg_root_hash, arg_root_hash_size, arg_flags, &m);
         if (r == -ENOPKG) {
                 log_error_errno(r, "Couldn't identify a suitable partition table or file system in %s.", arg_image);
                 goto finish;
diff --git a/src/machine/image-dbus.c b/src/machine/image-dbus.c
index 2b168b267b..1891f07586 100644
--- a/src/machine/image-dbus.c
+++ b/src/machine/image-dbus.c
@@ -336,7 +336,7 @@ static int raw_image_get_os_release(Image *image, char ***ret, sd_bus_error *err
         if (r < 0)
                 return sd_bus_error_set_errnof(error, r, "Failed to set up loop block device for %s: %m", image->path);
 
-        r = dissect_image(d->fd, NULL, 0, 0, &m);
+        r = dissect_image(d->fd, NULL, 0, DISSECT_IMAGE_REQUIRE_ROOT, &m);
         if (r == -ENOPKG)
                 return sd_bus_error_set_errnof(error, r, "Disk image %s not understood: %m", image->path);
         if (r < 0)
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 01d89df1a4..224d30fca6 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -3743,7 +3743,11 @@ int main(int argc, char *argv[]) {
                         goto finish;
                 }
 
-                r = dissect_image(loop->fd, arg_root_hash, arg_root_hash_size, 0, &dissected_image);
+                r = dissect_image(
+                                loop->fd,
+                                arg_root_hash, arg_root_hash_size,
+                                DISSECT_IMAGE_REQUIRE_ROOT,
+                                &dissected_image);
                 if (r == -ENOPKG) {
                         log_error_errno(r, "Could not find a suitable file system or partition table in image: %s", arg_image);
 
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
diff --git a/src/shared/dissect-image.h b/src/shared/dissect-image.h
index 76104e5780..26319bd8e7 100644
--- a/src/shared/dissect-image.h
+++ b/src/shared/dissect-image.h
@@ -69,6 +69,7 @@ typedef enum DissectImageFlags {
                                     DISSECT_IMAGE_DISCARD |
                                     DISSECT_IMAGE_DISCARD_ON_CRYPTO,
         DISSECT_IMAGE_GPT_ONLY = 16,         /* Only recognize images with GPT partition tables */
+        DISSECT_IMAGE_REQUIRE_ROOT = 32,     /* Don't accept disks without root partition */
 } DissectImageFlags;
 
 struct DissectedImage {
diff --git a/src/test/test-dissect-image.c b/src/test/test-dissect-image.c
index ddaf3a0d8b..2bb68be0db 100644
--- a/src/test/test-dissect-image.c
+++ b/src/test/test-dissect-image.c
@@ -43,7 +43,7 @@ int main(int argc, char *argv[]) {
                 return EXIT_FAILURE;
         }
 
-        r = dissect_image(d->fd, NULL, 0, 0, &m);
+        r = dissect_image(d->fd, NULL, 0, DISSECT_IMAGE_REQUIRE_ROOT, &m);
         if (r < 0) {
                 log_error_errno(r, "Failed to dissect image: %m");
                 return EXIT_FAILURE;