Re: Bug in the design of the tree search ioctl API ? [was Re: [PATCH 1/3] Btrfs: Really return keys within specified range]

[Li Zefan <lizf@cn.fujitsu.com>]

Goffredo Baroncelli wrote:
> On Wednesday, 15 December, 2010, Li Zefan wrote:
>> h4) objectid asis, type asis, offset++ -> we should get the correct result.
> 
> This fix the problem of the "missing subvolume". But for the other case 
> (searching for more than one type) the problem still here.
> 

I don't think so. And the above "h4" has showed how we search for more
than one type.

The generic userland code for next search is:

/* this is in essence the same as how we advance key in kernel code */
if (sk->min_offset < (u64)-1 && sk->min_offset < sk->max_offset)
	sk->min_offset++;
else if (sk->min_type < (u8)-1 && sk->min_type < sk->max_type) {
	sk->min_offset = 0;
	sk->min_type++;
} else if (sk->min_objectid < (u64)-1 && sk->min_objectid < sk->max_objectid){
	sk->min_offset = 0;
	sk->min_type = 0;
	sk->min_objectid++;
} else
	break;

ioctl(...);

for (i = 0; i < nr_items; i++) {
	if (!filter(items[i]))
		continue;
	/* process this item */
	...
}

>> because the current ioctl uses min_{x,y,z} and max_{x,y,z} as start_key and
>> end_key, and it returns all keys that falls in [start_key, end_key].
>>
>> So this btrfs-progs patch should fix missing subvolumes in the output of
>> "subvolume list":
>>
>> diff --git a/btrfs-list.c b/btrfs-list.c
>> index 93766a8..1b9ea45 100644
>> --- a/btrfs-list.c
>> +++ b/btrfs-list.c
>> @@ -620,7 +620,10 @@ int list_subvols(int fd)
>>                 /* this iteration is done, step forward one root for the 
> next
>>                  * ioctl
>>                  */
>> -               if (sk->min_objectid < (u64)-1) {
>> +               if (sk->min_type < BTRFS_ROOT_BACKREF_KEY) {
>> +                       sk->min_type = BTRFS_ROOT_BACKREF_KEY;
>> +                       sk->min_offset = 0;
>> +               } else  if (sk->min_objectid < (u64)-1) {
>>                         sk->min_objectid++;
>>                         sk->min_type = BTRFS_ROOT_BACKREF_KEY;
>>                         sk->min_offset = 0;
>>
> 
>