samples/vfs: add STATMOUNT_MNT_{G,U}IDMAP

Illustrate how to use STATMOUNT_MNT_{G,U}IDMAP.

Link: https://lore.kernel.org/r/20250204-work-mnt_idmap-statmount-v2-4-007720f39f2e@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

samples/vfs/samples-vfs.h

@@ -42,7 +42,11 @@ struct statmount {
 	__u32 opt_array;	/* [str] Array of nul terminated fs options */
 	__u32 opt_sec_num;	/* Number of security options */
 	__u32 opt_sec_array;	/* [str] Array of nul terminated security options */
-	__u64 __spare2[46];
+	__u32 mnt_uidmap_num;	/* Number of uid mappings */
+	__u32 mnt_uidmap;	/* [str] Array of uid mappings */
+	__u32 mnt_gidmap_num;	/* Number of gid mappings */
+	__u32 mnt_gidmap;	/* [str] Array of gid mappings */
+	__u64 __spare2[44];
 	char str[];		/* Variable size part containing strings */
 };
 
@@ -158,6 +162,14 @@ struct mnt_ns_info {
 #define STATX_MNT_ID_UNIQUE 0x00004000U /* Want/got extended stx_mount_id */
 #endif
 
+#ifndef STATMOUNT_MNT_UIDMAP
+#define STATMOUNT_MNT_UIDMAP		0x00002000U	/* Want/got uidmap... */
+#endif
+
+#ifndef STATMOUNT_MNT_GIDMAP
+#define STATMOUNT_MNT_GIDMAP		0x00004000U	/* Want/got gidmap... */
+#endif
+
 #ifndef MOUNT_ATTR_RDONLY
 #define MOUNT_ATTR_RDONLY	0x00000001 /* Mount read-only */
 #endif

samples/vfs/test-list-all-mounts.c

@@ -128,21 +128,43 @@ int main(int argc, char *argv[])
 					      STATMOUNT_MNT_POINT |
 					      STATMOUNT_MNT_NS_ID |
 					      STATMOUNT_MNT_OPTS |
-					      STATMOUNT_FS_TYPE, 0);
+					      STATMOUNT_FS_TYPE |
+					      STATMOUNT_MNT_UIDMAP |
+					      STATMOUNT_MNT_GIDMAP, 0);
 			if (!stmnt) {
 				printf("Failed to statmount(%" PRIu64 ") in mount namespace(%" PRIu64 ")\n",
 				       (uint64_t)last_mnt_id, (uint64_t)info.mnt_ns_id);
 				continue;
 			}
 
-			printf("mnt_id:\t\t%" PRIu64 "\nmnt_parent_id:\t%" PRIu64 "\nfs_type:\t%s\nmnt_root:\t%s\nmnt_point:\t%s\nmnt_opts:\t%s\n\n",
+			printf("mnt_id:\t\t%" PRIu64 "\nmnt_parent_id:\t%" PRIu64 "\nfs_type:\t%s\nmnt_root:\t%s\nmnt_point:\t%s\nmnt_opts:\t%s\n",
 			       (uint64_t)stmnt->mnt_id,
 			       (uint64_t)stmnt->mnt_parent_id,
 			       (stmnt->mask & STATMOUNT_FS_TYPE)   ? stmnt->str + stmnt->fs_type   : "",
 			       (stmnt->mask & STATMOUNT_MNT_ROOT)  ? stmnt->str + stmnt->mnt_root  : "",
 			       (stmnt->mask & STATMOUNT_MNT_POINT) ? stmnt->str + stmnt->mnt_point : "",
 			       (stmnt->mask & STATMOUNT_MNT_OPTS)  ? stmnt->str + stmnt->mnt_opts  : "");
 
+			if (stmnt->mask & STATMOUNT_MNT_UIDMAP) {
+				const char *idmap = stmnt->str + stmnt->mnt_uidmap;
+
+				for (size_t idx = 0; idx < stmnt->mnt_uidmap_num; idx++) {
+					printf("mnt_uidmap[%lu]:\t%s\n", idx, idmap);
+					idmap += strlen(idmap) + 1;
+				}
+			}
+
+			if (stmnt->mask & STATMOUNT_MNT_GIDMAP) {
+				const char *idmap = stmnt->str + stmnt->mnt_gidmap;
+
+				for (size_t idx = 0; idx < stmnt->mnt_gidmap_num; idx++) {
+					printf("mnt_gidmap[%lu]:\t%s\n", idx, idmap);
+					idmap += strlen(idmap) + 1;
+				}
+			}
+
+			printf("\n");
+
 			free(stmnt);
 		}
 	}