Allow moving file handles

lfs.c

@@ -503,7 +503,6 @@ static inline void lfs_superblock_tole32(lfs_superblock_t *superblock) {
 }
 #endif
 
-#ifndef LFS_NO_ASSERT
 static bool lfs_mlist_isopen(struct lfs_mlist *head,
         struct lfs_mlist *node) {
     for (struct lfs_mlist **p = &head; *p; p = &(*p)->next) {
@@ -514,7 +513,6 @@ static bool lfs_mlist_isopen(struct lfs_mlist *head,
 
     return false;
 }
-#endif
 
 static void lfs_mlist_remove(lfs_t *lfs, struct lfs_mlist *mlist) {
     for (struct lfs_mlist **p = &lfs->mlist; *p; p = &(*p)->next) {
@@ -6318,6 +6316,46 @@ lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file) {
     return res;
 }
 
+int lfs_file_movehandle(lfs_t *lfs, lfs_file_t *old_file, 
+        lfs_file_t *new_file) {
+    int err = LFS_LOCK(lfs->cfg);
+    if (err) {
+        return err;
+    }
+    LFS_TRACE("lfs_file_movehandle(%p, %p, %p)",
+            (void*)lfs, (void*)old_file, (void*)new_file);
+    LFS_ASSERT(lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)old_file));
+    LFS_ASSERT(!lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)new_file));
+
+    *new_file = *old_file;
+    lfs_mlist_remove(lfs, (struct lfs_mlist*)old_file);
+    lfs_mlist_append(lfs, (struct lfs_mlist*)new_file);
+
+    err = LFS_ERR_OK;
+
+    LFS_TRACE("lfs_file_movehandle -> %d", err);
+    LFS_UNLOCK(lfs->cfg);
+    return err;
+}
+
+int lfs_file_ishandleopen(lfs_t *lfs, lfs_file_t *file) {
+    int err = LFS_LOCK(lfs->cfg);
+    if (err) {
+        return err;
+    }
+    LFS_TRACE("lfs_file_ishandleopen(%p, %p)", (void*)lfs, (void*)file);
+
+    if (lfs_mlist_isopen(lfs->mlist, (struct lfs_mlist*)file)) {
+        err = LFS_ERR_OK;
+    } else {
+        err = LFS_ERR_BADF;    
+    }
+
+    LFS_TRACE("lfs_file_ishandleopen -> %d", err);
+    LFS_UNLOCK(lfs->cfg);
+    return err;
+}
+
 #ifndef LFS_READONLY
 int lfs_mkdir(lfs_t *lfs, const char *path) {
     int err = LFS_LOCK(lfs->cfg);

lfs.h

@@ -656,6 +656,20 @@ int lfs_file_rewind(lfs_t *lfs, lfs_file_t *file);
 // Returns the size of the file, or a negative error code on failure.
 lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file);
 
+// Move a file handle
+//
+// littlefs's file handles are somewhat expensive to move. Try to avoid
+// needing to move them. This allows moving a file handle from old_file
+// to new_file when needed for abstraction. After this call, old_file is
+// invalid.
+//
+// Returns a negative error code on failure.
+int lfs_file_movehandle(lfs_t *lfs, lfs_file_t *old_file, lfs_file_t *new_file);
+
+// Check if a given file handle is open
+//
+// Returns LFS_ERR_OK if the file handle is open, else LFS_ERR_BADF
+int lfs_file_ishandleopen(lfs_t *lfs, lfs_file_t *file);
 
 /// Directory operations ///
 

tests/test_files.toml

@@ -537,3 +537,61 @@ code = '''
     }
     lfs_unmount(&lfs) => 0;
 '''
+
+[cases.test_files_ishandleopen]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_file_t file;
+
+    lfs_file_ishandleopen(&lfs, &file) => LFS_ERR_BADF;
+
+    lfs_file_open(&lfs, &file, "hello", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+
+    lfs_file_ishandleopen(&lfs, &file) => 0;
+
+    lfs_file_close(&lfs, &file) => 0;
+
+    lfs_file_ishandleopen(&lfs, &file) => LFS_ERR_BADF;
+
+    lfs_unmount(&lfs) => 0;
+'''
+
+[cases.test_files_movehandle]
+defines.idx = [0, 1, 2]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    lfs_file_t file[3];
+    lfs_file_open(&lfs, &file[0], "a", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    lfs_file_open(&lfs, &file[1], "b", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    lfs_file_open(&lfs, &file[2], "c", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+
+    lfs_file_t file_new;
+    lfs_file_movehandle(&lfs, &file[idx], &file_new) => 0;
+
+    for (int i = 0; i < 3; i++) {
+        if (i == idx) {
+            continue;
+        }
+
+        lfs_file_ishandleopen(&lfs, &file[i]) => 0;
+    }
+    lfs_file_ishandleopen(&lfs, &file_new) => 0;
+
+    for (int i = 0; i < 3; i++) {
+        if (i == idx) {
+            continue;
+        }
+
+        lfs_file_close(&lfs, &file[i]) => 0;
+        lfs_file_ishandleopen(&lfs, &file[i]) => LFS_ERR_BADF;
+    }
+
+    lfs_file_close(&lfs, &file_new) => 0;
+    lfs_file_ishandleopen(&lfs, &file_new) => LFS_ERR_BADF;
+
+    lfs_unmount(&lfs) => 0;
+'''