Merge pull request #875 from littlefs-project/fs-gc

Add lfs_fs_gc to enable proactive finding of free blocks

lfs.c

@@ -622,6 +622,26 @@ static void lfs_alloc_drop(lfs_t *lfs) {
     lfs_alloc_ack(lfs);
 }
 
+#ifndef LFS_READONLY
+static int lfs_fs_rawgc(lfs_t *lfs) {
+    // Move free offset at the first unused block (lfs->free.i)
+    // lfs->free.i is equal lfs->free.size when all blocks are used
+    lfs->free.off = (lfs->free.off + lfs->free.i) % lfs->block_count;
+    lfs->free.size = lfs_min(8*lfs->cfg->lookahead_size, lfs->free.ack);
+    lfs->free.i = 0;
+
+    // find mask of free blocks from tree
+    memset(lfs->free.buffer, 0, lfs->cfg->lookahead_size);
+    int err = lfs_fs_rawtraverse(lfs, lfs_alloc_lookahead, lfs, true);
+    if (err) {
+        lfs_alloc_drop(lfs);
+        return err;
+    }
+
+    return 0;
+}
+#endif
+
 #ifndef LFS_READONLY
 static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
     while (true) {
@@ -654,16 +674,8 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
             return LFS_ERR_NOSPC;
         }
 
-        lfs->free.off = (lfs->free.off + lfs->free.size)
-                % lfs->block_count;
-        lfs->free.size = lfs_min(8*lfs->cfg->lookahead_size, lfs->free.ack);
-        lfs->free.i = 0;
-
-        // find mask of free blocks from tree
-        memset(lfs->free.buffer, 0, lfs->cfg->lookahead_size);
-        int err = lfs_fs_rawtraverse(lfs, lfs_alloc_lookahead, lfs, true);
-        if (err) {
-            lfs_alloc_drop(lfs);
+        int err = lfs_fs_rawgc(lfs);
+        if(err) {
             return err;
         }
     }
@@ -6238,6 +6250,22 @@ int lfs_fs_traverse(lfs_t *lfs, int (*cb)(void *, lfs_block_t), void *data) {
     return err;
 }
 
+#ifndef LFS_READONLY
+int lfs_fs_gc(lfs_t *lfs) {
+    int err = LFS_LOCK(lfs->cfg);
+    if (err) {
+        return err;
+    }
+    LFS_TRACE("lfs_fs_gc(%p)", (void*)lfs);
+
+    err = lfs_fs_rawgc(lfs);
+
+    LFS_TRACE("lfs_fs_gc -> %d", err);
+    LFS_UNLOCK(lfs->cfg);
+    return err;
+}
+#endif
+
 #ifndef LFS_READONLY
 int lfs_fs_mkconsistent(lfs_t *lfs) {
     int err = LFS_LOCK(lfs->cfg);

lfs.h

@@ -712,6 +712,18 @@ lfs_ssize_t lfs_fs_size(lfs_t *lfs);
 // Returns a negative error code on failure.
 int lfs_fs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
 
+// Attempt to proactively find free blocks
+//
+// Calling this function is not required, but may allowing the offloading of
+// the expensive block allocation scan to a less time-critical code path.
+//
+// Note: littlefs currently does not persist any found free blocks to disk.
+// This may change in the future.
+//
+// Returns a negative error code on failure. Finding no free blocks is
+// not an error.
+int lfs_fs_gc(lfs_t *lfs);
+
 #ifndef LFS_READONLY
 // Attempt to make the filesystem consistent and ready for writing
 //

tests/test_alloc.toml

@@ -6,6 +6,7 @@ if = 'BLOCK_CYCLES == -1'
 [cases.test_alloc_parallel]
 defines.FILES = 3
 defines.SIZE = '(((BLOCK_SIZE-8)*(BLOCK_COUNT-6)) / FILES)'
+defines.GC = [false, true]
 code = '''
     const char *names[] = {"bacon", "eggs", "pancakes"};
     lfs_file_t files[FILES];
@@ -24,6 +25,9 @@ code = '''
                 LFS_O_WRONLY | LFS_O_CREAT | LFS_O_APPEND) => 0;
     }
     for (int n = 0; n < FILES; n++) {
+        if (GC) {
+            lfs_fs_gc(&lfs) => 0;
+        }
         size_t size = strlen(names[n]);
         for (lfs_size_t i = 0; i < SIZE; i += size) {
             lfs_file_write(&lfs, &files[n], names[n], size) => size;
@@ -55,6 +59,7 @@ code = '''
 [cases.test_alloc_serial]
 defines.FILES = 3
 defines.SIZE = '(((BLOCK_SIZE-8)*(BLOCK_COUNT-6)) / FILES)'
+defines.GC = [false, true]
 code = '''
     const char *names[] = {"bacon", "eggs", "pancakes"};
 
@@ -75,6 +80,9 @@ code = '''
         uint8_t buffer[1024];
         memcpy(buffer, names[n], size);
         for (int i = 0; i < SIZE; i += size) {
+            if (GC) {
+                lfs_fs_gc(&lfs) => 0;
+            }
             lfs_file_write(&lfs, &file, buffer, size) => size;
         }
         lfs_file_close(&lfs, &file) => 0;
@@ -247,6 +255,9 @@ code = '''
     }
     res => LFS_ERR_NOSPC;
 
+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
+
     lfs_file_close(&lfs, &file) => 0;
     lfs_unmount(&lfs) => 0;
 
@@ -298,6 +309,9 @@ code = '''
     }
     res => LFS_ERR_NOSPC;
 
+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
+
     lfs_file_close(&lfs, &file) => 0;
     lfs_unmount(&lfs) => 0;
 
@@ -337,6 +351,8 @@ code = '''
         count += 1;
     }
     err => LFS_ERR_NOSPC;
+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
     lfs_file_close(&lfs, &file) => 0;
 
     lfs_remove(&lfs, "exhaustion") => 0;
@@ -435,6 +451,8 @@ code = '''
             break;
         }
     }
+    // note that lfs_fs_gc should not error here
+    lfs_fs_gc(&lfs) => 0;
     lfs_file_close(&lfs, &file) => 0;
 
     lfs_unmount(&lfs) => 0;