[Xenomai] [PATCH] analogy: fix __a4l_get_sbsize() if device has only one subdevice

[Jan Leupold]

Am 12.12.2016 um 16:55 schrieb Jorge Ramirez:
> On 12/07/2016 01:39 PM, Jan Leupold wrote:
>> All a4l_sbinfo_t are handled in __a4l_fill_desc() as a contiguous array
>> and is stored as data in a4l_root_t. The old code allocated enough
>> memory when the device had at least two subdevices, but missed 8 bytes
>> (on ARM32), which is the difference between sizeof(a4l_root_t) and
>> sizeof(a4l_leaf_t).
> 
> sorry I dont understand this patch. could you expand on the scenario you
> are testing?

Scenario: one a4l device with exactly one a4l subdevice with one channel
and one range. A call to a4l_fill_desc() then returns -ENOMEM, which is
caused by a check at the beginning of a4l_leaf_add().

> a4l_root_setup already takes into consideration the size of the a4l_root_t
> (check the offset initialization)

My interpretation of what should be constructed in sbdata memory is this:

+---------------------------------
|r|s|s|s|s|...|s|l|c|c|c|...
+---------------------------------
                ^
r = a4l_root_t
s = a4l_sbinfo_t
l = a4l_leaf_t
c = a4l_chinfo_t

What I mean is: the root stores the whole array of all subdevice info and
its size must be "root + n * sbinfo" (this is where the ^ points to).
But __a4l_get_sbsize() is implemented as "n * (leaf + sbinfo)". root and
leaf differ in size.

As soon as the a4l device has more than one subdevice (n > 1) always enough
memory is allocated. But for n == 1 the size difference between a4l_root_t
and a4l_leaf_t is not taken into account. a4l_root_setup() sets the offset
correctly according to sizeof(a4l_root_t), but __a4l_get_sbsize() used
sizeof(a4l_leaf_t) to calculate it.

Memory size for channel and range info is also calculated as
"n * (leaf + info)" and could be reduced to "leaf + n * info", but
out-of-memory is not an issue here.

> 
> 
> 
>> ---
>>  lib/analogy/descriptor.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/analogy/descriptor.c b/lib/analogy/descriptor.c
>> index bc4d7bd..fa8cf93 100644
>> --- a/lib/analogy/descriptor.c
>> +++ b/lib/analogy/descriptor.c
>> @@ -100,8 +100,9 @@ static inline a4l_leaf_t *a4l_leaf_get(a4l_leaf_t * lf,
>>  static int __a4l_get_sbsize(int fd, a4l_desc_t * dsc)
>>  {
>>  	unsigned int i, j, nb_chan, nb_rng;
>> +	/* all subdevice a4l_sbinfo_t are within one special leaf: the root */
>>  	int ret, res =
>> -		dsc->nb_subd * (sizeof(a4l_sbinfo_t) + sizeof(a4l_leaf_t));
>> +		sizeof(a4l_root_t) + dsc->nb_subd * (sizeof(a4l_sbinfo_t));
>>  
>>  	for (i = 0; i < dsc->nb_subd; i++) {
>>  
>>
>>
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> 


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