dissect: split read-only flag into two

Let's have one flag to request that when dissecting an image the
loopback device is made read-only, and another one to request that when
it is mounted to make it read-only. Previously both concepts were always
done read-only together.

(Of course, making the loopback device read-only but mounting it
read-write doesn't make too much sense, but the kernel should catch that
for us, no need to make restrictions from our side there)

Use-case for this: in systemd-repart we'd like to operate on images for
adding partitions. Thus we'd like to have the loopback device writable,
but if we read repart.d/ snippets from it, we want to do that read-only.

src/core/namespace.c

@@ -1853,7 +1853,7 @@ int setup_namespace(
 
                 r = loop_device_make_by_path(
                                 root_image,
-                                FLAGS_SET(dissect_image_flags, DISSECT_IMAGE_READ_ONLY) ? O_RDONLY : -1 /* < 0 means writable if possible, read-only as fallback */,
+                                FLAGS_SET(dissect_image_flags, DISSECT_IMAGE_DEVICE_READ_ONLY) ? O_RDONLY : -1 /* < 0 means writable if possible, read-only as fallback */,
                                 FLAGS_SET(dissect_image_flags, DISSECT_IMAGE_NO_PARTITION_TABLE) ? 0 : LO_FLAGS_PARTSCAN,
                                 &loop_device);
                 if (r < 0)

src/dissect/dissect.c

@@ -770,7 +770,7 @@ static int run(int argc, char *argv[]) {
 
         r = loop_device_make_by_path(
                         arg_image,
-                        FLAGS_SET(arg_flags, DISSECT_IMAGE_READ_ONLY) ? O_RDONLY : O_RDWR,
+                        FLAGS_SET(arg_flags, DISSECT_IMAGE_DEVICE_READ_ONLY) ? O_RDONLY : O_RDWR,
                         FLAGS_SET(arg_flags, DISSECT_IMAGE_NO_PARTITION_TABLE) ? 0 : LO_FLAGS_PARTSCAN,
                         &d);
         if (r < 0)

src/shared/dissect-image.c

@@ -1408,7 +1408,7 @@ static int mount_partition(
         if (streq(fstype, "crypto_LUKS"))
                 return -EUNATCH;
 
-        rw = m->rw && !(flags & DISSECT_IMAGE_READ_ONLY);
+        rw = m->rw && !(flags & DISSECT_IMAGE_MOUNT_READ_ONLY);
 
         if (FLAGS_SET(flags, DISSECT_IMAGE_FSCK) && rw) {
                 r = run_fsck(node, fstype);
@@ -1756,7 +1756,7 @@ static int decrypt_partition(
                 return log_debug_errno(r, "Failed to load LUKS metadata: %m");
 
         r = sym_crypt_activate_by_passphrase(cd, name, CRYPT_ANY_SLOT, passphrase, strlen(passphrase),
-                                             ((flags & DISSECT_IMAGE_READ_ONLY) ? CRYPT_ACTIVATE_READONLY : 0) |
+                                             ((flags & DISSECT_IMAGE_DEVICE_READ_ONLY) ? CRYPT_ACTIVATE_READONLY : 0) |
                                              ((flags & DISSECT_IMAGE_DISCARD_ON_CRYPTO) ? CRYPT_ACTIVATE_ALLOW_DISCARDS : 0));
         if (r < 0) {
                 log_debug_errno(r, "Failed to activate LUKS device: %m");
@@ -2674,7 +2674,7 @@ int mount_image_privately_interactively(
 
         r = loop_device_make_by_path(
                         image,
-                        FLAGS_SET(flags, DISSECT_IMAGE_READ_ONLY) ? O_RDONLY : O_RDWR,
+                        FLAGS_SET(flags, DISSECT_IMAGE_DEVICE_READ_ONLY) ? O_RDONLY : O_RDWR,
                         FLAGS_SET(flags, DISSECT_IMAGE_NO_PARTITION_TABLE) ? 0 : LO_FLAGS_PARTSCAN,
                         &d);
         if (r < 0)

src/shared/dissect-image.h

@@ -87,13 +87,13 @@ static inline PartitionDesignator PARTITION_VERITY_OF(PartitionDesignator p) {
 }
 
 typedef enum DissectImageFlags {
-        DISSECT_IMAGE_READ_ONLY           = 1 << 0,
+        DISSECT_IMAGE_DEVICE_READ_ONLY    = 1 << 0,  /* Make device read-only */
         DISSECT_IMAGE_DISCARD_ON_LOOP     = 1 << 1,  /* Turn on "discard" if on a loop device and file system supports it */
         DISSECT_IMAGE_DISCARD             = 1 << 2,  /* Turn on "discard" if file system supports it, on all block devices */
         DISSECT_IMAGE_DISCARD_ON_CRYPTO   = 1 << 3,  /* Turn on "discard" also on crypto devices */
-        DISSECT_IMAGE_DISCARD_ANY = DISSECT_IMAGE_DISCARD_ON_LOOP |
-                                    DISSECT_IMAGE_DISCARD |
-                                    DISSECT_IMAGE_DISCARD_ON_CRYPTO,
+        DISSECT_IMAGE_DISCARD_ANY         = DISSECT_IMAGE_DISCARD_ON_LOOP |
+                                            DISSECT_IMAGE_DISCARD |
+                                            DISSECT_IMAGE_DISCARD_ON_CRYPTO,
         DISSECT_IMAGE_GPT_ONLY            = 1 << 4,  /* Only recognize images with GPT partition tables */
         DISSECT_IMAGE_GENERIC_ROOT        = 1 << 5,  /* If no partition table or only single generic partition, assume it's the root fs */
         DISSECT_IMAGE_MOUNT_ROOT_ONLY     = 1 << 6,  /* Mount only the root and /usr partitions */
@@ -107,6 +107,9 @@ typedef enum DissectImageFlags {
         DISSECT_IMAGE_MKDIR               = 1 << 14, /* Make top-level directory to mount right before mounting, if missing */
         DISSECT_IMAGE_USR_NO_ROOT         = 1 << 15, /* If no root fs is in the image, but /usr is, then allow this (so that we can mount the rootfs as tmpfs or so */
         DISSECT_IMAGE_REQUIRE_ROOT        = 1 << 16, /* Don't accept disks without root partition (or at least /usr partition if DISSECT_IMAGE_USR_NO_ROOT is set) */
+        DISSECT_IMAGE_MOUNT_READ_ONLY     = 1 << 17, /* Make mounts read-only */
+        DISSECT_IMAGE_READ_ONLY           = DISSECT_IMAGE_DEVICE_READ_ONLY |
+                                            DISSECT_IMAGE_MOUNT_READ_ONLY,
 } DissectImageFlags;
 
 struct DissectedImage {