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Added sticky-bit for preventing file syncs after write errors

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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.
This commit is contained in:
Christopher Haster
2017-11-16 17:25:41 -06:00
parent 2612e1b3fa
commit 843e3c6c75
3 changed files with 28 additions and 10 deletions
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lfs.c
+8 -1
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@@ -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;
}