Re: [PATCH v2 04/17] IB/core: Add umem function to read data from user-space

[Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 10/12/2014 18:22, Yann Droneaud wrote:
> Hi,
> 
> Le mardi 11 novembre 2014 à 18:36 +0200, Haggai Eran a écrit :
>> In some drivers there's a need to read data from a user space area that
>> was pinned using ib_umem, when running from a different process context.
>>
>> The ib_umem_copy_from function allows reading data from the physical pages
>> pinned in the ib_umem struct.
>>
>> Signed-off-by: Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
>> ---
>>  drivers/infiniband/core/umem.c | 26 ++++++++++++++++++++++++++
>>  include/rdma/ib_umem.h         |  2 ++
>>  2 files changed, 28 insertions(+)
>>
>> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
>> index e0f883292374..77bec75963e7 100644
>> --- a/drivers/infiniband/core/umem.c
>> +++ b/drivers/infiniband/core/umem.c
>> @@ -292,3 +292,29 @@ int ib_umem_page_count(struct ib_umem *umem)
>>  	return n;
>>  }
>>  EXPORT_SYMBOL(ib_umem_page_count);
>> +
>> +/*
>> + * Copy from the given ib_umem's pages to the given buffer.
>> + *
>> + * umem - the umem to copy from
>> + * offset - offset to start copying from
>> + * dst - destination buffer
>> + * length - buffer length
>> + *
>> + * Returns the number of copied bytes, or an error code.
>> + */
>> +int ib_umem_copy_from(struct ib_umem *umem, size_t offset, void *dst,
>> +		      size_t length)
> 
> I would prefer the arguments in the same order as ib_copy_from_udata()
> 
> int ib_umem_copy_from(void *dst,
>                       struct ib_umem *umem, size_t umem_offset,
>                       size_t length);

No problem.

>> +{
>> +	size_t end = offset + length;
>> +
>> +	if (offset > umem->length || end > umem->length || end < offset) {
>> +		pr_err("ib_umem_copy_from not in range. offset: %zd umem length: %zd end: %zd\n",
>> +		       offset, umem->length, end);
>> +		return -EINVAL;
>> +	}
>> +
>> +	return sg_pcopy_to_buffer(umem->sg_head.sgl, umem->nmap, dst, length,
>> +			offset + ib_umem_offset(umem));
>> +}
>> +EXPORT_SYMBOL(ib_umem_copy_from);
> 
> As the function return a "int", no more than INT_MAX bytes (likely 2^31
> - 1) can be copied. Perhaps changing the return type to to ssize_t would
> be better (and a check to enfore ssize_t maximum value). Or change the
> function could return 0 in case of success or a error code, just like
> ib_copy_from_udata().
> 

Okay. I'll change it to match ib_copy_from_udata. We're checking the
umem size in the call site of this function anyway, and the only reason
I see sg_pcopy_to_buffer would return less than *length* bytes is when
reaching the end of the scatterlist.

Haggai
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