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

[Alex Williamson <alex.williamson@redhat.com>]

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);
}

Thanks,
Alex

>   		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.  
> >   
>