[nrf fromlist] fs: nvs: Improve nvs_calc_free_space() result precision

The nvs_calc_free_space() function does not return 0 when the NVS
is considered full, because some special ATEs are not taken into account.

This commit takes into account the ATE that is reserved for deletion in
each sector, in addition of the 'GC done' ATE when present.

Upstream PR: zephyrproject-rtos/zephyr#74900

Signed-off-by: Adrien Ricciardi <[email protected]>

Author: RICCIARDI-Adrien

subsys/fs/nvs/nvs.c

@@ -1355,7 +1355,11 @@ ssize_t nvs_calc_free_space(struct nvs_fs *fs)
 
 	free_space = 0;
 	for (uint16_t i = 1; i < fs->sector_count; i++) {
-		free_space += (fs->sector_size - ate_size);
+		/*
+		 * There is always a closing ATE and a reserved ATE for
+		 * deletion in each sector
+		 */
+		free_space += (fs->sector_size - (2 * ate_size));
 	}
 
 	step_addr = fs->ate_wra;
@@ -1379,11 +1383,17 @@ ssize_t nvs_calc_free_space(struct nvs_fs *fs)
 			}
 		}
 
-		if ((wlk_addr == step_addr) && step_ate.len &&
-		    (nvs_ate_valid(fs, &step_ate))) {
-			/* count needed */
-			free_space -= nvs_al_size(fs, step_ate.len);
-			free_space -= ate_size;
+		if (nvs_ate_valid(fs, &step_ate)) {
+			/* Take into account the GC done ATE if it is present */
+			if (step_ate.len == 0) {
+				if (step_ate.id == 0xFFFF) {
+					free_space -= ate_size;
+				}
+			} else if (wlk_addr == step_addr) {
+				/* count needed */
+				free_space -= nvs_al_size(fs, step_ate.len);
+				free_space -= ate_size;
+			}
 		}
 
 		if (step_addr == fs->ate_wra) {