Mention that shrinking is unlikely to work

.github/workflows/test.yml

@@ -374,6 +374,22 @@ jobs:
         run: |
           CFLAGS="$CFLAGS -DLFS_NO_INTRINSICS" make test
 
+  test-shrink:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: install
+        run: |
+          # need a few things
+          sudo apt-get update -qq
+          sudo apt-get install -qq gcc python3 python3-pip
+          pip3 install toml
+          gcc --version
+          python3 --version
+      - name: test-no-intrinsics
+        run: |
+          CFLAGS="$CFLAGS -DLFS_SHRINKIFCHEAP" make test
+
   # run with all trace options enabled to at least make sure these
   # all compile
   test-yes-trace:

lfs.h

@@ -766,11 +766,11 @@ int lfs_fs_gc(lfs_t *lfs);
 // Grows the filesystem to a new size, updating the superblock with the new
 // block count.
 //
-// if LFS_SHRINKIFCHEAP is defined, this function will also accept
+// If LFS_SHRINKIFCHEAP is defined, this function will also accept
 // block_counts smaller than the current configuration, after checking
 // that none of the blocks that are being removed are in use.
-//
-// Note: This is irreversible.
+// Note that littlefs's pseudorandom block allocation means that
+// this is very unlikely to work in the general case.
 //
 // Returns a negative error code on failure.
 int lfs_fs_grow(lfs_t *lfs, lfs_size_t block_count);

tests/test_shrink.toml

@@ -2,8 +2,10 @@
 [cases.test_shrink_simple]
 defines.BLOCK_COUNT = [10, 15, 20]
 defines.AFTER_BLOCK_COUNT = [5, 10, 15, 19]
+   
 if = "AFTER_BLOCK_COUNT <= BLOCK_COUNT"
 code = '''
+#ifdef LFS_SHRINKIFCHEAP
     lfs_t lfs;
     lfs_format(&lfs, cfg) => 0;
     lfs_mount(&lfs, cfg) => 0;
@@ -18,6 +20,7 @@ code = '''
     lfs2.cfg = &cfg2;
     lfs_mount(&lfs2, &cfg2) => 0;
     lfs_unmount(&lfs2) => 0;
+#endif
 '''
 
 # shrinking full
@@ -27,6 +30,7 @@ defines.AFTER_BLOCK_COUNT = [5, 7, 10, 12, 15, 17, 20]
 defines.FILES_COUNT = [7, 8, 9, 10]
 if = "AFTER_BLOCK_COUNT <= BLOCK_COUNT && FILES_COUNT + 2 < BLOCK_COUNT"
 code = '''
+#ifdef LFS_SHRINKIFCHEAP
     lfs_t lfs;
     lfs_format(&lfs, cfg) => 0;
     // create FILES_COUNT files of BLOCK_SIZE - 50 bytes (to avoid inlining)
@@ -101,4 +105,5 @@ code = '''
         }
         lfs_unmount(&lfs2);
     }
+#endif
 '''

tests/test_superblocks.toml

@@ -531,6 +531,7 @@ defines.BLOCK_COUNT = 'ERASE_COUNT'
 defines.BLOCK_COUNT_2 = ['ERASE_COUNT/2', 'ERASE_COUNT/4', '2']
 defines.KNOWN_BLOCK_COUNT = [true, false]
 code = '''
+#ifdef LFS_SHRINKIFCHEAP
     lfs_t lfs;
     lfs_format(&lfs, cfg) => 0;
 
@@ -628,6 +629,7 @@ code = '''
     lfs_file_close(&lfs, &file) => 0;
     assert(memcmp(buffer, "hello!", 6) == 0);
     lfs_unmount(&lfs) => 0;
+#endif
 '''
 
 # test that metadata_max does not cause problems for superblock compaction