On 2019/6/9 2:50 上午, Rolf Fokkens wrote:
> On 6/8/19 12:22 PM, Coly Li wrote:
>> +static inline void preceding_key(struct bkey *k, struct bkey
>> *preceding_key_p)
>> +{
>> + if (KEY_INODE(k) || KEY_OFFSET(k)) {
>> + *preceding_key_p = KEY(KEY_INODE(k), KEY_OFFSET(k), 0);
>> + if (!preceding_key_p->low)
>> + preceding_key_p->high--;
>> + preceding_key_p->low--;
>> + } else {
>> + preceding_key_p = NULL;
>
> If I'm correct, the line above has no net effect, it just changes a
> local variable (parameter) with no effect elsewhere. So the else part
> may be left out, or do you mean this?
>
> *preceding_key_p = ZERO_KEY;
>
Hi Rolf and Pierre,
Setting preceding_key_p to NULL is for the following
bch_btree_iter_init(). See the call chains
bch_btree_insert_key()->bch_btree_iter_init()->
__bch_btree_iter_init()->bch_bset_search()
preceding_key_p is parameter 'search' in bch_bset_search().
If it is NULL, t->data->start returns directly; if it is not NULL,
__bch_bset_search() is called.
Indeed *preceding_key_p = ZERO_KEY is unnecessary, just makes me
comfortable. The problem is PRECEDING_KEY() allocates an on-stack
variable, and this one is overlapped with stackframe of
bch_btree_iter_init(), and overwritten. Because this anonymous on-stack
variable is allocated inside PRECEDING_KEY(), not (and should not be)
protected by compiler.
So I add the new local variable preceding_key (and make preceding_key_p
points to it) explicitly on stack frame of bch_btree_insert_key(), which
will never be overlapped with stackframe of bch_btree_iter_init().
Thanks.
--
Coly Li
