repart: make No-Auto GPT partition flag configurable too

This is useful for provisioning initially empty secondary A/B root file
systems. We don't want those to ever be considered for automatic
mounting, for example in "systemd-nspawn --image=", hence we should
create them with the No-Auto flag turned on. Once a file system image is
dropped into the partition the flag may be turned off by the updater
tool, so that it is considered from then on.

Thew new option for this is called NoAuto. I dislike negated options
like this, but this is taken from the naming in the spec, which in turn
inherited the name from the same flag for Microsoft Data Partitions. To
minimize confusion, let's stick to the name hence.

src/partition/repart.c

@@ -169,6 +169,7 @@ struct Partition {
         EncryptMode encrypt;
 
         uint64_t gpt_flags;
+        int no_auto;
         int read_only;
         int growfs;
 
@@ -243,6 +244,7 @@ static Partition *partition_new(void) {
                 .offset = UINT64_MAX,
                 .copy_blocks_fd = -1,
                 .copy_blocks_size = UINT64_MAX,
+                .no_auto = -1,
                 .read_only = -1,
                 .growfs = -1,
         };
@@ -1312,6 +1314,7 @@ static int partition_read_definition(Partition *p, const char *path) {
                 { "Partition", "Encrypt",         config_parse_encrypt,     0, &p->encrypt          },
                 { "Partition", "Flags",           config_parse_gpt_flags,   0, &p->gpt_flags        },
                 { "Partition", "ReadOnly",        config_parse_tristate,    0, &p->read_only        },
+                { "Partition", "NoAuto",          config_parse_tristate,    0, &p->no_auto          },
                 { "Partition", "GrowFileSystem",  config_parse_tristate,    0, &p->growfs           },
                 {}
         };
@@ -3269,6 +3272,17 @@ static uint64_t partition_merge_flags(Partition *p) {
 
         f = p->gpt_flags;
 
+        if (p->no_auto >= 0) {
+                if (gpt_partition_type_knows_no_auto(p->type_uuid))
+                        SET_FLAG(f, GPT_FLAG_NO_AUTO, p->no_auto);
+                else {
+                        char buffer[ID128_UUID_STRING_MAX];
+                        log_warning("Configured NoAuto=%s for partition type '%s' that doesn't support it, ignoring.",
+                                    yes_no(p->no_auto),
+                                    gpt_partition_type_uuid_to_string_harder(p->type_uuid, buffer));
+                }
+        }
+
         if (p->read_only >= 0) {
                 if (gpt_partition_type_knows_read_only(p->type_uuid))
                         SET_FLAG(f, GPT_FLAG_READ_ONLY, p->read_only);
@@ -3409,7 +3423,7 @@ static int context_mangle_partitions(Context *context) {
                         if (r < 0)
                                 return log_error_errno(r, "Failed to set partition label: %m");
 
-                        /* Merge the read only + growfs setting with the literal flags, and set them for the partition */
+                        /* Merge the no auto + read only + growfs setting with the literal flags, and set them for the partition */
                         r = set_gpt_flags(q, partition_merge_flags(p));
                         if (r < 0)
                                 return log_error_errno(r, "Failed to set GPT partition flags: %m");

src/shared/gpt.c

@@ -174,3 +174,17 @@ bool gpt_partition_type_knows_growfs(sd_id128_t id) {
                                 GPT_TMP,
                                 GPT_XBOOTLDR);
 }
+
+bool gpt_partition_type_knows_no_auto(sd_id128_t id) {
+        return gpt_partition_type_is_root(id) ||
+                gpt_partition_type_is_root_verity(id) ||
+                gpt_partition_type_is_usr(id) ||
+                gpt_partition_type_is_usr_verity(id) ||
+                sd_id128_in_set(id,
+                                GPT_HOME,
+                                GPT_SRV,
+                                GPT_VAR,
+                                GPT_TMP,
+                                GPT_XBOOTLDR,
+                                GPT_SWAP);
+}

src/shared/gpt.h

@@ -140,3 +140,4 @@ bool gpt_partition_type_is_usr_verity(sd_id128_t id);
 
 bool gpt_partition_type_knows_read_only(sd_id128_t id);
 bool gpt_partition_type_knows_growfs(sd_id128_t id);
+bool gpt_partition_type_knows_no_auto(sd_id128_t id);