Added sticky-bit for preventing file syncs after write errors

Short story, files are no longer committed to directories during
file sync/close if the last write did not complete successfully.
This avoids a set of interesting user-experience issues related
to the end-of-life behaviour of the filesystem.

As a filesystem approaches end-of-life, the chances of running into
LFS_ERR_NOSPC grows rather quickly. Since this condition occurs after
at the end of a devices life, it's likely that operating in these
conditions hasn't been tested thoroughly.

In the specific case of file-writes, you can hit an LFS_ERR_NOSPC after
parts of the file have been written out. If the program simply continues
and closes the file, the file is written out half completed. Since
littlefs has a strong garuntee the prevents half-writes, it's unlikely
this state of the file would be expected.

To make things worse, since close is also responsible for memory
cleanup, it's actually _impossible_ to continue working as it was
without leaking memory.

By prevent the file commits, end-of-life behaviour should at least retain
a previous copy of the filesystem without any surprises.

1 files changed, 8 insertions, 1 deletions

diff --git a/lfs.c b/lfs.c
index eea7ae3..6088b4e 100644
--- a/lfs.c
+++ b/lfs.c
@@ -1403,7 +1403,9 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
         return err;
     }
 
-    if ((file->flags & LFS_F_DIRTY) && !lfs_pairisnull(file->pair)) {
+    if ((file->flags & LFS_F_DIRTY) &&
+            !(file->flags & LFS_F_ERRED) &&
+            !lfs_pairisnull(file->pair)) {
         // update dir entry
         lfs_dir_t cwd;
         int err = lfs_dir_fetch(lfs, &cwd, file->pair);
@@ -1537,6 +1539,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
                         file->head, file->size,
                         file->pos-1, &file->block, &file->off);
                 if (err) {
+                    file->flags |= LFS_F_ERRED;
                     return err;
                 }
 
@@ -1550,6 +1553,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
                     file->block, file->pos,
                     &file->block, &file->off);
             if (err) {
+                file->flags |= LFS_F_ERRED;
                 return err;
             }
 
@@ -1565,6 +1569,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
                 if (err == LFS_ERR_CORRUPT) {
                     goto relocate;
                 }
+                file->flags |= LFS_F_ERRED;
                 return err;
             }
 
@@ -1572,6 +1577,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
 relocate:
             err = lfs_file_relocate(lfs, file);
             if (err) {
+                file->flags |= LFS_F_ERRED;
                 return err;
             }
         }
@@ -1584,6 +1590,7 @@ relocate:
         lfs_alloc_ack(lfs);
     }
 
+    file->flags &= ~LFS_F_ERRED;
     return size;
 }