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Tweaked lfsr_file_open to only sync when unsynced

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Do'h! I almost forgot about LFS_O_TRUNC. If LFS_O_CREAT + LFS_O_SYNC
implies lfsr_file_sync, clearly LFS_O_TRUNC + LFS_O_SYNC should as well.

This changes lfsr_file_open to only imply lfsr_file_sync if any open
operation sets the unsync flag, which is the only case where
lfsr_file_sync would do anything anyways.

This does have a subtle change in behavior when LFS_O_CREAT + LFS_O_SYNC
+ LFS_O_DESYNC, in that the desync flag is only cleared if the file did
not exist before. But I think this is more expected than unconditionally
syncing.

Note this matches the behavior of lfsr_file_write, which does _not_
imply lfsr_file_sync if the write is size=0.

---

Also added better tests over lfsr_file_open + LFS_O_TRUNC, this flag
isn't very well tested...

Which found a bug!

We were incorrectly setting LFS_o_UNFLUSH when opening with LFS_O_TRUNC,
when we should have set LFS_o_UNSYNC. This caused littlefs to never
bother updating the file's metadata unless some other write comes along
(which is what usually follows LFS_O_TRUNC).

To help catch bugs like this, I added an assert to lfsr_file_flush that
unflushed files are always marked unsynced. A synced + unflushed file is
weird and should never happen.

---

Code changes minimal:

           code          stack          ctx
  before: 35820           2480          640
  after:  35824 (+0.0%)   2480 (+0.0%)  640 (+0.0%)
This commit is contained in:
Christopher Haster
2025-04-26 01:28:00 -05:00
parent 4b87499605
commit 7b81f01db4
2 changed files with 129 additions and 22 deletions
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tests/test_fsync.toml
+114 -14
View File
@@ -160,8 +160,27 @@ code = '''
assert(memcmp(rbuf, "hello!", strlen("hello!")) == 0);
lfsr_file_close(&lfs, &c) => 0;
// lets rewrite a
lfsr_file_rewind(&lfs, &a) => 0;
// reopen with LFS_O_TRUNC
lfsr_file_close(&lfs, &a) => 0;
lfsr_file_open(&lfs, &a, "jello",
LFS_O_WRONLY
| LFS_O_TRUNC
| ((FLUSH == 2) ? LFS_O_FLUSH : 0)
| ((SYNC == 2) ? LFS_O_SYNC : 0)) => 0;
// should immediately show up in b
lfsr_file_read(&lfs, &b, rbuf, sizeof(rbuf)) => 0;
// and on disk
lfsr_file_open(&lfs, &c, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => 0;
lfsr_file_close(&lfs, &c) => 0;
// reopen LFS_O_WRONLY and rewrite a
lfsr_file_close(&lfs, &a) => 0;
lfsr_file_open(&lfs, &a, "jello",
LFS_O_WRONLY
| ((FLUSH == 2) ? LFS_O_FLUSH : 0)
| ((SYNC == 2) ? LFS_O_SYNC : 0)) => 0;
lfsr_file_write(&lfs, &a, "bonjour!", strlen("bonjour!"))
=> strlen("bonjour!");
@@ -405,19 +424,77 @@ code = '''
assert(memcmp(rbuf, "bonjour!", strlen("bonjour!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// lets rewrite a one last time
lfsr_file_rewind(&lfs, &a) => 0;
lfsr_file_write(&lfs, &a, "ohayo!", strlen("ohayo!"))
// reopen b with LFS_O_TRUNC
lfsr_file_close(&lfs, &b) => 0;
lfsr_file_open(&lfs, &b, "jello",
LFS_O_WRONLY
| LFS_O_TRUNC
| ((FLUSH == 2) ? LFS_O_FLUSH : 0)
| ((SYNC == 2) ? LFS_O_SYNC : 0)) => 0;
// should immediately show up in c
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => 0;
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => 0;
lfsr_file_close(&lfs, &d) => 0;
// sync a
lfsr_file_sync(&lfs, &a) => 0;
// a's contents were clobbered, so we should see b
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => 0;
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => 0;
lfsr_file_close(&lfs, &d) => 0;
// reopen LFS_O_WRONLY and rewrite b
lfsr_file_close(&lfs, &b) => 0;
lfsr_file_open(&lfs, &b, "jello",
LFS_O_WRONLY
| ((FLUSH == 2) ? LFS_O_FLUSH : 0)
| ((SYNC == 2) ? LFS_O_SYNC : 0)) => 0;
lfsr_file_write(&lfs, &b, "ohayo!", strlen("ohayo!"))
=> strlen("ohayo!");
// should immediately show up in c
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("ohayo!r!");
assert(memcmp(rbuf, "ohayo!r!", strlen("ohayo!r!")) == 0);
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("ohayo!");
assert(memcmp(rbuf, "ohayo!", strlen("ohayo!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("ohayo!r!");
assert(memcmp(rbuf, "ohayo!r!", strlen("ohayo!r!")) == 0);
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("ohayo!");
assert(memcmp(rbuf, "ohayo!", strlen("ohayo!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// sync a
lfsr_file_sync(&lfs, &a) => 0;
// a's contents were clobbered, so we should see b
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("ohayo!");
assert(memcmp(rbuf, "ohayo!", strlen("ohayo!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("ohayo!");
assert(memcmp(rbuf, "ohayo!", strlen("ohayo!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// lets rewrite a one last time
lfsr_file_rewind(&lfs, &a) => 0;
lfsr_file_write(&lfs, &a, "zdrasti!", strlen("zdrasti!"))
=> strlen("zdrasti!");
// should immediately show up in c
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("zdrasti!");
assert(memcmp(rbuf, "zdrasti!", strlen("zdrasti!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("zdrasti!");
assert(memcmp(rbuf, "zdrasti!", strlen("zdrasti!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// close a and b
@@ -426,12 +503,12 @@ code = '''
// should still have a
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("ohayo!r!");
assert(memcmp(rbuf, "ohayo!r!", strlen("ohayo!r!")) == 0);
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("zdrasti!");
assert(memcmp(rbuf, "zdrasti!", strlen("zdrasti!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("ohayo!r!");
assert(memcmp(rbuf, "ohayo!r!", strlen("ohayo!r!")) == 0);
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("zdrasti!");
assert(memcmp(rbuf, "zdrasti!", strlen("zdrasti!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
lfsr_file_close(&lfs, &c) => 0;
@@ -2474,7 +2551,30 @@ code = '''
assert(memcmp(rbuf, "hello!", strlen("hello!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// write to a
// reopen with LFS_O_TRUNC
lfsr_file_close(&lfs, &a) => 0;
lfsr_file_open(&lfs, &a, "jello",
LFS_O_WRONLY
| LFS_O_TRUNC
| ((FLUSH == 2) ? LFS_O_FLUSH : 0)
| ((SYNC == 2) ? LFS_O_SYNC : 0)
| LFS_O_DESYNC) => 0;
// should immediately show up in c
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => 0;
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => 0;
lfsr_file_close(&lfs, &d) => 0;
// reopen LFS_O_WRONLY and rewrite a
lfsr_file_close(&lfs, &a) => 0;
lfsr_file_open(&lfs, &a, "jello",
LFS_O_WRONLY
| ((FLUSH == 2) ? LFS_O_FLUSH : 0)
| ((SYNC == 2) ? LFS_O_SYNC : 0)
| LFS_O_DESYNC) => 0;
lfsr_file_write(&lfs, &a, "bonjour!", strlen("bonjour!"))
=> strlen("bonjour!");