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Fixed lfs_file_truncate issue where internal state may not be flushed

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This was caused by the new lfs_file_rawseek optimization that can skip
flushing when calculated file->pos is unchanged combined with an
implicit expectation in lfs_file_truncate that lfs_file_rawseek
unconditionally sets file->pos.

Because of this assumption, lfs_file_truncate could leave file->pos in
an outdated state while changing the internal file metadata. Humorously,
this was always gauranteed to trigger the skip in lfs_file_rawseek when
we try to restore the file->pos, leaving the file->cache used to do the
CTZ skip-list lookup in a potentially bad state.

The easiest fix is to just update file->pos correctly. Note we don't
want to explicitly flush since we can leverage the same noop
optimization if we truncate to the file position. Which I've added a
test for.
This commit is contained in:
Christopher Haster 2021-01-11 00:01:05 -06:00
parent 3216b07c3b
commit 745d98cde0
2 changed files with 48 additions and 0 deletions
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3
lfs.c
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@ -3106,6 +3106,9 @@ static int lfs_file_rawtruncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size) {
return err;
}
// need to set pos/block/off consistently so seeking back to
// the old position does not get confused
file->pos = size;
file->ctz.head = file->block;
file->ctz.size = size;
file->flags |= LFS_F_DIRTY | LFS_F_READING;

45
tests/test_truncate.toml
View File

@ -392,3 +392,48 @@ code = '''
lfs_unmount(&lfs) => 0;
'''
[[case]] # noop truncate
define.MEDIUMSIZE = [32, 2048]
code = '''
lfs_format(&lfs, &cfg) => 0;
lfs_mount(&lfs, &cfg) => 0;
lfs_file_open(&lfs, &file, "baldynoop",
LFS_O_RDWR | LFS_O_CREAT) => 0;
strcpy((char*)buffer, "hair");
size = strlen((char*)buffer);
for (lfs_off_t j = 0; j < MEDIUMSIZE; j += size) {
lfs_file_write(&lfs, &file, buffer, size) => size;
// this truncate should do nothing
lfs_file_truncate(&lfs, &file, j+size) => 0;
}
lfs_file_size(&lfs, &file) => MEDIUMSIZE;
lfs_file_seek(&lfs, &file, 0, LFS_SEEK_SET) => 0;
// should do nothing again
lfs_file_truncate(&lfs, &file, MEDIUMSIZE) => 0;
lfs_file_size(&lfs, &file) => MEDIUMSIZE;
for (lfs_off_t j = 0; j < MEDIUMSIZE; j += size) {
lfs_file_read(&lfs, &file, buffer, size) => size;
memcmp(buffer, "hair", size) => 0;
}
lfs_file_read(&lfs, &file, buffer, size) => 0;
lfs_file_close(&lfs, &file) => 0;
lfs_unmount(&lfs) => 0;
// still there after reboot?
lfs_mount(&lfs, &cfg) => 0;
lfs_file_open(&lfs, &file, "baldynoop", LFS_O_RDWR) => 0;
lfs_file_size(&lfs, &file) => MEDIUMSIZE;
for (lfs_off_t j = 0; j < MEDIUMSIZE; j += size) {
lfs_file_read(&lfs, &file, buffer, size) => size;
memcmp(buffer, "hair", size) => 0;
}
lfs_file_read(&lfs, &file, buffer, size) => 0;
lfs_file_close(&lfs, &file) => 0;
lfs_unmount(&lfs) => 0;
'''