Re: [PATCH v2 1/4] ida: Add ida_get_lowest()

[Yi Liu <yi.l.liu@intel.com>]

On 2024/4/19 00:23, Alex Williamson wrote:
> On Thu, 18 Apr 2024 15:02:46 +0800
> Yi Liu <yi.l.liu@intel.com> wrote:
> 
>> On 2024/4/17 00:03, Alex Williamson wrote:
>>> On Fri, 12 Apr 2024 01:21:18 -0700
>>> Yi Liu <yi.l.liu@intel.com> wrote:
>>>    
>>>> There is no helpers for user to check if a given ID is allocated or not,
>>>> neither a helper to loop all the allocated IDs in an IDA and do something
>>>> for cleanup. With the two needs, a helper to get the lowest allocated ID
>>>> of a range can help to achieve it.
>>>>
>>>> Caller can check if a given ID is allocated or not by:
>>>> 	int id = 200, rc;
>>>>
>>>> 	rc = ida_get_lowest(&ida, id, id);
>>>> 	if (rc == id)
>>>> 		//id 200 is used
>>>> 	else
>>>> 		//id 200 is not used
>>>>
>>>> Caller can iterate all allocated IDs by:
>>>> 	int id = 0;
>>>>
>>>> 	while (!ida_is_empty(&pasid_ida)) {
>>>> 		id = ida_get_lowest(pasid_ida, id, INT_MAX);
>>>> 		if (id < 0)
>>>> 			break;
>>>> 		//anything to do with the allocated ID
>>>> 		ida_free(pasid_ida, pasid);
>>>> 	}
>>>>
>>>> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
>>>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
>>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>>> ---
>>>>    include/linux/idr.h |  1 +
>>>>    lib/idr.c           | 67 +++++++++++++++++++++++++++++++++++++++++++++
>>>>    2 files changed, 68 insertions(+)
>>>>
>>>> diff --git a/include/linux/idr.h b/include/linux/idr.h
>>>> index da5f5fa4a3a6..1dae71d4a75d 100644
>>>> --- a/include/linux/idr.h
>>>> +++ b/include/linux/idr.h
>>>> @@ -257,6 +257,7 @@ struct ida {
>>>>    int ida_alloc_range(struct ida *, unsigned int min, unsigned int max, gfp_t);
>>>>    void ida_free(struct ida *, unsigned int id);
>>>>    void ida_destroy(struct ida *ida);
>>>> +int ida_get_lowest(struct ida *ida, unsigned int min, unsigned int max);
>>>>    
>>>>    /**
>>>>     * ida_alloc() - Allocate an unused ID.
>>>> diff --git a/lib/idr.c b/lib/idr.c
>>>> index da36054c3ca0..03e461242fe2 100644
>>>> --- a/lib/idr.c
>>>> +++ b/lib/idr.c
>>>> @@ -476,6 +476,73 @@ int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
>>>>    }
>>>>    EXPORT_SYMBOL(ida_alloc_range);
>>>>    
>>>> +/**
>>>> + * ida_get_lowest - Get the lowest used ID.
>>>> + * @ida: IDA handle.
>>>> + * @min: Lowest ID to get.
>>>> + * @max: Highest ID to get.
>>>> + *
>>>> + * Get the lowest used ID between @min and @max, inclusive.  The returned
>>>> + * ID will not exceed %INT_MAX, even if @max is larger.
>>>> + *
>>>> + * Context: Any context. Takes and releases the xa_lock.
>>>> + * Return: The lowest used ID, or errno if no used ID is found.
>>>> + */
>>>> +int ida_get_lowest(struct ida *ida, unsigned int min, unsigned int max)
>>>> +{
>>>> +	unsigned long index = min / IDA_BITMAP_BITS;
>>>> +	unsigned int offset = min % IDA_BITMAP_BITS;
>>>> +	unsigned long *addr, size, bit;
>>>> +	unsigned long flags;
>>>> +	void *entry;
>>>> +	int ret;
>>>> +
>>>> +	if (min >= INT_MAX)
>>>> +		return -EINVAL;
>>>> +	if (max >= INT_MAX)
>>>> +		max = INT_MAX;
>>>> +
>>>
>>> Could these be made consistent with the test in ida_alloc_range(), ie:
>>>
>>> 	if ((int)min < 0)
>>> 		return -EINVAL;
>>> 	if ((int)max < 0)
>>> 		max = INT_MAX;
>>>    
>>
>> sure.
>>
>>>> +	xa_lock_irqsave(&ida->xa, flags);
>>>> +
>>>> +	entry = xa_find(&ida->xa, &index, max / IDA_BITMAP_BITS, XA_PRESENT);
>>>> +	if (!entry) {
>>>> +		ret = -ENOTTY;
>>>
>>> -ENOENT?  Same for all below too.
>>
>> I see.
>>
>>>> +		goto err_unlock;
>>>> +	}
>>>> +
>>>> +	if (index > min / IDA_BITMAP_BITS)
>>>> +		offset = 0;
>>>> +	if (index * IDA_BITMAP_BITS + offset > max) {
>>>> +		ret = -ENOTTY;
>>>> +		goto err_unlock;
>>>> +	}
>>>> +
>>>> +	if (xa_is_value(entry)) {
>>>> +		unsigned long tmp = xa_to_value(entry);
>>>> +
>>>> +		addr = &tmp;
>>>> +		size = BITS_PER_XA_VALUE;
>>>> +	} else {
>>>> +		addr = ((struct ida_bitmap *)entry)->bitmap;
>>>> +		size = IDA_BITMAP_BITS;
>>>> +	}
>>>> +
>>>> +	bit = find_next_bit(addr, size, offset);
>>>> +
>>>> +	xa_unlock_irqrestore(&ida->xa, flags);
>>>> +
>>>> +	if (bit == size ||
>>>> +	    index * IDA_BITMAP_BITS + bit > max)
>>>> +		return -ENOTTY;
>>>> +
>>>> +	return index * IDA_BITMAP_BITS + bit;
>>>> +
>>>> +err_unlock:
>>>> +	xa_unlock_irqrestore(&ida->xa, flags);
>>>> +	return ret;
>>>> +}
>>>> +EXPORT_SYMBOL(ida_get_lowest);
>>>
>>> The API is a bit awkward to me, I wonder if it might be helped with
>>> some renaming and wrappers...
>>>
>>> int ida_find_first_range(struct ida *ida, unsigned int min, unsigned int max);
>>
>> ok.
>>
>>> bool ida_exists(struct ida *ida, unsigned int id)
>>> {
>>> 	return ida_find_first_range(ida, id, id) == id;
>>> }
>>
>> this does helps in next patch.
>>
>>>
>>> int ida_find_first(struct ida *ida)
>>> {
>>> 	return ida_find_first_range(ida, 0, ~0);
>>> }
>>>   
>>
>> perhaps it can be added in future. This series has two usages. One is to
>> check if a given ID is allocated. This can be covered by your ida_exists().
>> Another usage is to loop each IDs, do detach and free. This can still use
>> the ida_find_first_range() like the example in the commit message. The
>> first loop starts from 0, and next would start from the last found ID.
>> This may be more efficient than starts from 0 in every loop.
>>
>>
>>> _min and _max variations of the latter would align with existing
>>> ida_alloc variants, but maybe no need to add them preemptively.
>>
>> yes.
>>
>>> Possibly an ida_for_each() could be useful in the use case of
>>> disassociating each id, but not required for the brute force iterative
>>> method.  Thanks,
>>
>> yep. maybe we can start with the below code, no need for ida_for_each()
>> today.
>>
>>
>>    	int id = 0;
>>
>>    	while (!ida_is_empty(&pasid_ida)) {
>>    		id = ida_find_first_range(pasid_ida, id, INT_MAX);
> 
> You've actually already justified the _min function here:
> 
> static inline int ida_find_first_min(struct ida *ida, unsigned int min)
> {
> 	return ida_find_first_range(ida, min, ~0);
> }

aha, I see. :)

> 
>>    		if (unlikely(WARN_ON(id < 0))
>> 			break;
>>    		iommufd_device_pasid_detach();
>>    		ida_free(pasid_ida, pasid);
>>    	}
>>
>>>    
>>>> +
>>>>    /**
>>>>     * ida_free() - Release an allocated ID.
>>>>     * @ida: IDA handle.
>>>    
>>
> 
> 

-- 
Regards,
Yi Liu