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Fixed lookahead overflow and removed unbounded lookahead pointers

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As pointed out by davidefer, the lookahead pointer modular arithmetic
does not work around integer overflow when the pointer size is not a
multiple of the block count.

To avoid overflow problems, the easy solution is to stop trying to
work around integer overflows and keep the lookahead offset inside the
block device. To make this work, the ack was modified into a resetable
counter that is decremented every block allocation.

As a plus, quite a bit of the allocation logic ended up simplified.
This commit is contained in:
Christopher Haster
2018-04-10 15:14:27 -05:00
parent 6a89ecba39
commit f935fc0be6
3 changed files with 29 additions and 28 deletions
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9
tests/test_alloc.sh
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@@ -120,17 +120,16 @@ do
tests/test.py << TEST
lfs_mount(&lfs, &cfg) => 0;
// setup lookahead to almost overflow
lfs.free.begin = ((lfs_size_t)-1) - $SIZE/(2*cfg.block_size);
lfs.free.size = 0;
lfs.free.off = 0;
// // setup lookahead to almost overflow
// lfs.free.begin = ((lfs_size_t)-1) - 2*$SIZE;
// lfs.free.size = 0;
// lfs.free.off = 0;
lfs_file_open(&lfs, &file[0], "overflow/$name",
LFS_O_WRONLY | LFS_O_CREAT | LFS_O_APPEND) => 0;
size = strlen("$name");
memcpy(buffer, "$name", size);
for (int i = 0; i < $SIZE; i++) {
printf("%d\n", lfs.free.begin);
lfs_file_write(&lfs, &file[0], buffer, size) => size;
}
lfs_file_close(&lfs, &file[0]) => 0;