util/disk_cache: Add marker on cache usage.

To be able to delete it later if it isn't used. Checking the mtime
on e.g. the index doesn't work if we always hit the cache so add
something that writes unconditionally.

Only once per day to avoid excessive writes.

(See https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22339)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27173>

src/util/disk_cache.c

@@ -146,6 +146,9 @@ disk_cache_type_create(const char *gpu_name,
          goto path_fail;
    }
 
+   if (!getenv("MESA_SHADER_CACHE_DIR") && !getenv("MESA_GLSL_CACHE_DIR"))
+      disk_cache_touch_cache_user_marker(cache->path);
+
    cache->type = cache_type;
 
    cache->stats.enabled = debug_get_bool_option("MESA_SHADER_CACHE_SHOW_STATS",

src/util/disk_cache_os.c

@@ -96,6 +96,7 @@ disk_cache_get_function_identifier(void *ptr, struct mesa_sha1 *ctx)
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include "utime.h"
 
 #include "util/blob.h"
 #include "util/crc32.h"
@@ -1044,6 +1045,29 @@ disk_cache_load_cache_index_foz(void *mem_ctx, struct disk_cache *cache)
    return foz_prepare(&cache->foz_db, cache->path);
 }
 
+
+void
+disk_cache_touch_cache_user_marker(char *path)
+{
+   char *marker_path = NULL;
+   asprintf(&marker_path, "%s/marker", path);
+   if (!marker_path)
+      return;
+
+   time_t now = time(NULL);
+
+   struct stat attr;
+   if (stat(marker_path, &attr) == -1) {
+      int fd = open(marker_path, O_WRONLY | O_CREAT | O_CLOEXEC, 0644);
+      if (fd != -1) {
+         close(fd);
+      }
+   } else if (now - attr.st_mtime < 60 * 60 * 24 /* One day */) {
+      (void)utime(marker_path, NULL);
+   }
+   free(marker_path);
+}
+
 bool
 disk_cache_mmap_cache_index(void *mem_ctx, struct disk_cache *cache,
                             char *path)

src/util/disk_cache_os.h

@@ -161,6 +161,9 @@ disk_cache_enabled(void);
 bool
 disk_cache_load_cache_index_foz(void *mem_ctx, struct disk_cache *cache);
 
+void
+disk_cache_touch_cache_user_marker(char *path);
+
 bool
 disk_cache_mmap_cache_index(void *mem_ctx, struct disk_cache *cache,
                             char *path);