Re: [PATCH V8 15/33] aio: add aio support for iov_iter arguments

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Sorry for the lack of response. Getting back to this.

On 08/21/2013 08:55 AM, Benjamin LaHaise wrote:
> On Thu, Jul 25, 2013 at 12:50:41PM -0500, Dave Kleikamp wrote:
>> This adds iocb cmds which specify that memory is held in iov_iter
>> structures.  This lets kernel callers specify memory that can be
>> expressed in an iov_iter, which includes pages in bio_vec arrays.
>>
>> Only kernel callers can provide an iov_iter so it doesn't make a lot of
>> sense to expose the IOCB_CMD values for this as part of the user space
>> ABI.
> 
> I don't think adding the IOCB_CMD_{READ,WRITE}_ITER operations to 
> include/uapi/linux/aio_abi.h is the right thing to do here -- they're 
> never going to be used by userland, and care certainly not part of the 
> abi we're presenting to userland.  I'd suggest moving these opcodes to 
> include/linux/aio.h.

Agreed.

> Also, if you make the values > 16 bits, userland 
> will never be able to pass them in inadvertently (although things look 
> okay if that does happen at present).

I'd have to change the declaration of ki_opcode to an int. This
shouldn't be a problem since it'll be padded to a long anyway.

> 
> 		-ben
> 
>> But kernel callers should also be able to perform the usual aio
>> operations which suggests using the the existing operation namespace and
>> support code.
>>
>> Signed-off-by: Dave Kleikamp <dave.kleikamp@xxxxxxxxxx>
>> Cc: Zach Brown <zab@xxxxxxxxx>
>> ---
>>  fs/aio.c                     | 67 ++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/aio.h          |  3 ++
>>  include/uapi/linux/aio_abi.h |  2 ++
>>  3 files changed, 72 insertions(+)
>>
>> diff --git a/fs/aio.c b/fs/aio.c
>> index c65ba13..0da82c0 100644
>> --- a/fs/aio.c
>> +++ b/fs/aio.c
>> @@ -991,6 +991,48 @@ static ssize_t aio_setup_single_vector(int rw, struct kiocb *kiocb)
>>  	return 0;
>>  }
>>  
>> +static ssize_t aio_read_iter(struct kiocb *iocb)
>> +{
>> +	struct file *file = iocb->ki_filp;
>> +	ssize_t ret;
>> +
>> +	if (unlikely(!is_kernel_kiocb(iocb)))
>> +		return -EINVAL;
>> +
>> +	if (unlikely(!(file->f_mode & FMODE_READ)))
>> +		return -EBADF;
>> +
>> +	ret = security_file_permission(file, MAY_READ);
>> +	if (unlikely(ret))
>> +		return ret;
>> +
>> +	if (!file->f_op->read_iter)
>> +		return -EINVAL;
>> +
>> +	return file->f_op->read_iter(iocb, iocb->ki_iter, iocb->ki_pos);
>> +}
>> +
>> +static ssize_t aio_write_iter(struct kiocb *iocb)
>> +{
>> +	struct file *file = iocb->ki_filp;
>> +	ssize_t ret;
>> +
>> +	if (unlikely(!is_kernel_kiocb(iocb)))
>> +		return -EINVAL;
>> +
>> +	if (unlikely(!(file->f_mode & FMODE_WRITE)))
>> +		return -EBADF;
>> +
>> +	ret = security_file_permission(file, MAY_WRITE);
>> +	if (unlikely(ret))
>> +		return ret;
>> +
>> +	if (!file->f_op->write_iter)
>> +		return -EINVAL;
>> +
>> +	return file->f_op->write_iter(iocb, iocb->ki_iter, iocb->ki_pos);
>> +}
>> +
>>  /*
>>   * aio_setup_iocb:
>>   *	Performs the initial checks and aio retry method
>> @@ -1042,6 +1084,14 @@ rw_common:
>>  		ret = aio_rw_vect_retry(req, rw, rw_op);
>>  		break;
>>  
>> +	case IOCB_CMD_READ_ITER:
>> +		ret = aio_read_iter(req);
>> +		break;
>> +
>> +	case IOCB_CMD_WRITE_ITER:
>> +		ret = aio_write_iter(req);
>> +		break;
>> +
>>  	case IOCB_CMD_FDSYNC:
>>  		if (!file->f_op->aio_fsync)
>>  			return -EINVAL;
>> @@ -1116,6 +1166,23 @@ void aio_kernel_init_rw(struct kiocb *iocb, struct file *filp,
>>  }
>>  EXPORT_SYMBOL_GPL(aio_kernel_init_rw);
>>  
>> +/*
>> + * The iter count must be set before calling here.  Some filesystems uses
>> + * iocb->ki_left as an indicator of the size of an IO.
>> + */
>> +void aio_kernel_init_iter(struct kiocb *iocb, struct file *filp,
>> +			  unsigned short op, struct iov_iter *iter, loff_t off)
>> +{
>> +	iocb->ki_filp = filp;
>> +	iocb->ki_iter = iter;
>> +	iocb->ki_opcode = op;
>> +	iocb->ki_pos = off;
>> +	iocb->ki_nbytes = iov_iter_count(iter);
>> +	iocb->ki_left = iocb->ki_nbytes;
>> +	iocb->ki_ctx = (void *)-1;
>> +}
>> +EXPORT_SYMBOL_GPL(aio_kernel_init_iter);
>> +
>>  void aio_kernel_init_callback(struct kiocb *iocb,
>>  			      void (*complete)(u64 user_data, long res),
>>  			      u64 user_data)
>> diff --git a/include/linux/aio.h b/include/linux/aio.h
>> index 014a75d..64d059d 100644
>> --- a/include/linux/aio.h
>> +++ b/include/linux/aio.h
>> @@ -66,6 +66,7 @@ struct kiocb {
>>  	 * this is the underlying eventfd context to deliver events to.
>>  	 */
>>  	struct eventfd_ctx	*ki_eventfd;
>> +	struct iov_iter		*ki_iter;
>>  };
>>  
>>  static inline bool is_sync_kiocb(struct kiocb *kiocb)
>> @@ -102,6 +103,8 @@ struct kiocb *aio_kernel_alloc(gfp_t gfp);
>>  void aio_kernel_free(struct kiocb *iocb);
>>  void aio_kernel_init_rw(struct kiocb *iocb, struct file *filp,
>>  			unsigned short op, void *ptr, size_t nr, loff_t off);
>> +void aio_kernel_init_iter(struct kiocb *iocb, struct file *filp,
>> +			  unsigned short op, struct iov_iter *iter, loff_t off);
>>  void aio_kernel_init_callback(struct kiocb *iocb,
>>  			      void (*complete)(u64 user_data, long res),
>>  			      u64 user_data);
>> diff --git a/include/uapi/linux/aio_abi.h b/include/uapi/linux/aio_abi.h
>> index bb2554f..22ce4bd 100644
>> --- a/include/uapi/linux/aio_abi.h
>> +++ b/include/uapi/linux/aio_abi.h
>> @@ -44,6 +44,8 @@ enum {
>>  	IOCB_CMD_NOOP = 6,
>>  	IOCB_CMD_PREADV = 7,
>>  	IOCB_CMD_PWRITEV = 8,
>> +	IOCB_CMD_READ_ITER = 9,
>> +	IOCB_CMD_WRITE_ITER = 10,
>>  };
>>  
>>  /*
>> -- 
>> 1.8.3.4
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