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Reverted LFS_O_SYNC implicit noop sync broadcasting

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Reading more into POSIX, it seems that most of the write functions do
have special behavior built into what would implicitly be a noop.

It's difficult to find, since it usually doesn't matter, but consider
the m_time field. The following operations do _not_ update m_time:

- write when size=0
- truncate when size does not change
- fruncate when size does not change

I think it's safe to extend these to sync broadcasts in littlefs, and
only guarantee sync broadcasts when the file state has changed (even
though that may mean other file handles may remain out-of-date!).

In this interpretation, the "write operations" described in POSIX more
mean the implicit write operations effected by write/truncate/fruncate.

That being said, it's not clear what the best approach is, desync files
make this all a bit more muddled... This may also be reverted.
This commit is contained in:
Christopher Haster
2024-01-10 20:12:06 -06:00
parent 4e7a68ff08
commit 122864f4b6
2 changed files with 4 additions and 125 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lfs.c
+4 -7
View File
@@ -10520,9 +10520,8 @@ lfs_ssize_t lfsr_file_write(lfs_t *lfs, lfsr_file_t *file,
// underlying file, this means no updating file pos or file size
//
// since we need to test for this, just return early
lfs_size_t written = 0;
if (size == 0) {
goto noop;
return 0;
}
// checkpoint the allocator
@@ -10549,6 +10548,7 @@ lfs_ssize_t lfsr_file_write(lfs_t *lfs, lfsr_file_t *file,
}
const uint8_t *buffer_ = buffer;
lfs_size_t written = 0;
while (size > 0) {
// bypass buffer?
//
@@ -10631,7 +10631,6 @@ lfs_ssize_t lfsr_file_write(lfs_t *lfs, lfsr_file_t *file,
// update our pos
file->pos = pos;
noop:;
// flush if requested
//
// this seems unreachable, but it's possible if we transition from
@@ -10874,7 +10873,7 @@ int lfsr_file_truncate(lfs_t *lfs, lfsr_file_t *file, lfs_off_t size_) {
// do nothing if our size does not change
lfs_off_t size = lfsr_file_size_(file);
if (lfsr_file_size_(file) == size_) {
goto noop;
return 0;
}
// checkpoint the allocator
@@ -10943,7 +10942,6 @@ int lfsr_file_truncate(lfs_t *lfs, lfsr_file_t *file, lfs_off_t size_) {
// mark as unsynced
file->flags |= LFS_F_UNSYNCED;
noop:;
// flush if requested
//
// this seems unreachable, but it's possible if we transition from
@@ -10980,7 +10978,7 @@ int lfsr_file_fruncate(lfs_t *lfs, lfsr_file_t *file, lfs_off_t size_) {
// do nothing if our size does not change
lfs_off_t size = lfsr_file_size_(file);
if (size == size_) {
goto noop;
return 0;
}
// checkpoint the allocator
@@ -11077,7 +11075,6 @@ int lfsr_file_fruncate(lfs_t *lfs, lfsr_file_t *file, lfs_off_t size_) {
// mark as unsynced
file->flags |= LFS_F_UNSYNCED;
noop:;
// flush if requested
//
// this seems unreachable, but it's possible if we transition from
tests/test_fsync.toml
-118
View File
@@ -2085,124 +2085,6 @@ code = '''
lfsr_unmount(&lfs) => 0;
'''
[cases.test_fsync_desync_wdwdrr_noop_creative]
# there's several clever ways we can noop...
# TODO flush()?
# 0 => sync()
# 1 => write(0)
# 2 => truncate(size)
# 3 => fruncate(size)
defines.NOOP = [0, 1, 2, 3]
code = '''
lfs_t lfs;
lfsr_format(&lfs, CFG) => 0;
lfsr_mount(&lfs, CFG) => 0;
// a - writer
// b - syncing writer
// c - reader kept open, recvs updates from a
// d - reader kept closed, checks disk state
lfsr_file_t a;
lfsr_file_t b;
lfsr_file_t c;
lfsr_file_t d;
uint8_t rbuf[256];
lfsr_file_open(&lfs, &a, "jello",
LFS_O_WRONLY | LFS_O_CREAT | LFS_O_EXCL) => 0;
lfsr_file_open(&lfs, &b, "jello", LFS_O_WRONLY | LFS_O_SYNC) => 0;
lfsr_file_open(&lfs, &c, "jello", LFS_O_RDONLY) => 0;
// write to a and sync
lfsr_file_write(&lfs, &a, "hello!", strlen("hello!"))
=> strlen("hello!");
lfsr_file_sync(&lfs, &a) => 0;
// our write should show up in c
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("hello!");
assert(memcmp(rbuf, "hello!", strlen("hello!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("hello!");
assert(memcmp(rbuf, "hello!", strlen("hello!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// mark b as desync, this should freeze its contents
lfsr_file_desync(&lfs, &b) => 0;
// rewrite a, sync
lfsr_file_rewind(&lfs, &a) => 0;
lfsr_file_write(&lfs, &a, "bonjour!", strlen("bonjour!"))
=> strlen("bonjour!");
lfsr_file_sync(&lfs, &a) => 0;
// a should show up in c
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("bonjour!");
assert(memcmp(rbuf, "bonjour!", strlen("bonjour!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("bonjour!");
assert(memcmp(rbuf, "bonjour!", strlen("bonjour!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// sync b, _creatively_, dragons be here
if (NOOP == 0) {
lfsr_file_sync(&lfs, &b) => 0;
} else if (NOOP == 1) {
lfsr_file_write(&lfs, &b, NULL, 0) => 0;
} else if (NOOP == 2) {
lfsr_file_size(&lfs, &b) => strlen("hello!");
lfsr_file_truncate(&lfs, &b, strlen("hello!")) => 0;
} else if (NOOP == 3) {
lfsr_file_size(&lfs, &b) => strlen("hello!");
lfsr_file_fruncate(&lfs, &b, strlen("hello!")) => 0;
}
// b should show up in c, without a's changes
lfsr_file_rewind(&lfs, &c) => 0;
lfsr_file_read(&lfs, &c, rbuf, sizeof(rbuf)) => strlen("hello!");
assert(memcmp(rbuf, "hello!", strlen("hello!")) == 0);
// and on disk
lfsr_file_open(&lfs, &d, "jello", LFS_O_RDONLY) => 0;
lfsr_file_read(&lfs, &d, rbuf, sizeof(rbuf)) => strlen("hello!");
assert(memcmp(rbuf, "hello!", strlen("hello!")) == 0);
lfsr_file_close(&lfs, &d) => 0;
// rewrite b, close, desync flag should have been cleared
lfsr_file_rewind(&lfs, &b) => 0;
lfsr_file_write(&lfs, &b, "ohayo!", strlen("ohayo!"))
=> strlen("ohayo!");
lfsr_file_close(&lfs, &b) => 0;
// our write should show up in c
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;
// rewrite a, close
lfsr_file_rewind(&lfs, &a) => 0;
lfsr_file_write(&lfs, &a, "zdrasti!", strlen("zdrasti!"))
=> strlen("zdrasti!");
lfsr_file_close(&lfs, &a) => 0;
// our write should 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;
lfsr_file_close(&lfs, &c) => 0;
lfsr_unmount(&lfs) => 0;
'''
[cases.test_fsync_desync_wdwdrr_append]
code = '''
lfs_t lfs;