[lttng-dev] UST check pointer/de-reference order

[Mathieu Desnoyers]

* Oestman, Fredrik (Fredrik_Oestman at mentor.com) wrote:
> I stumbled across some code where pointers are de-referenced and then checked for NULL.
> 
> Cheers,

merged into master and stable-2.0, thanks!

Mathieu

> 
> Fredrik Östman
> 
> 
> diff --git a/liblttng-ust-ctl/ustctl.c b/liblttng-ust-ctl/ustctl.c
> index 9789413..80aed04 100644
> --- a/liblttng-ust-ctl/ustctl.c
> +++ b/liblttng-ust-ctl/ustctl.c
> @@ -732,7 +732,7 @@ void ustctl_unmap_channel(struct lttng_ust_shm_handle *handle)
>  struct lttng_ust_lib_ring_buffer *ustctl_open_stream_read(struct lttng_ust_shm_handle *handle,
>  	int cpu)
>  {
> -	struct channel *chan = handle->shadow_chan;
> +	struct channel *chan;
>  	int *shm_fd, *wait_fd;
>  	uint64_t *memory_map_size;
>  	struct lttng_ust_lib_ring_buffer *buf;
> @@ -741,6 +741,7 @@ struct lttng_ust_lib_ring_buffer *ustctl_open_stream_read(struct lttng_ust_shm_h
>  	if (!handle)
>  		return NULL;
>  
> +	chan = handle->shadow_chan;
>  	buf = channel_get_ring_buffer(&chan->backend.config,
>  		chan, cpu, handle, &shm_fd, &wait_fd, &memory_map_size);
>  	if (!buf)
> @@ -784,11 +785,12 @@ int ustctl_get_mmap_len(struct lttng_ust_shm_handle *handle,
>  		unsigned long *len)
>  {
>  	unsigned long mmap_buf_len;
> -	struct channel *chan = handle->shadow_chan;
> +	struct channel *chan;
>  
>  	if (!handle || !buf || !len)
>  		return -EINVAL;
>  
> +	chan = handle->shadow_chan;
>  	if (chan->backend.config.output != RING_BUFFER_MMAP)
>  		return -EINVAL;
>  	mmap_buf_len = chan->backend.buf_size;
> @@ -805,11 +807,12 @@ int ustctl_get_max_subbuf_size(struct lttng_ust_shm_handle *handle,
>  		struct lttng_ust_lib_ring_buffer *buf,
>  		unsigned long *len)
>  {
> -	struct channel *chan = handle->shadow_chan;
> +	struct channel *chan;
>  
>  	if (!handle || !buf || !len)
>  		return -EINVAL;
>  
> +	chan = handle->shadow_chan;
>  	*len = chan->backend.subbuf_size;
>  	return 0;
>  }
> @@ -823,12 +826,13 @@ int ustctl_get_max_subbuf_size(struct lttng_ust_shm_handle *handle,
>  int ustctl_get_mmap_read_offset(struct lttng_ust_shm_handle *handle,
>  		struct lttng_ust_lib_ring_buffer *buf, unsigned long *off)
>  {
> -	struct channel *chan = handle->shadow_chan;
> +	struct channel *chan;
>  	unsigned long sb_bindex;
>  
>  	if (!handle || !buf || !off)
>  		return -EINVAL;
>  
> +	chan = handle->shadow_chan;
>  	if (chan->backend.config.output != RING_BUFFER_MMAP)
>  		return -EINVAL;
>  	sb_bindex = subbuffer_id_get_index(&chan->backend.config,
> @@ -841,11 +845,12 @@ int ustctl_get_mmap_read_offset(struct lttng_ust_shm_handle *handle,
>  int ustctl_get_subbuf_size(struct lttng_ust_shm_handle *handle,
>  		struct lttng_ust_lib_ring_buffer *buf, unsigned long *len)
>  {
> -	struct channel *chan = handle->shadow_chan;
> +	struct channel *chan;
>  
>  	if (!handle || !buf || !len)
>  		return -EINVAL;
>  
> +	chan = handle->shadow_chan;
>  	*len = lib_ring_buffer_get_read_data_size(&chan->backend.config, buf,
>  		handle);
>  	return 0;
> @@ -855,11 +860,12 @@ int ustctl_get_subbuf_size(struct lttng_ust_shm_handle *handle,
>  int ustctl_get_padded_subbuf_size(struct lttng_ust_shm_handle *handle,
>  		struct lttng_ust_lib_ring_buffer *buf, unsigned long *len)
>  {
> -	struct channel *chan = handle->shadow_chan;
> +	struct channel *chan;
>  
>  	if (!handle || !buf || !len)
>  		return -EINVAL;
>  
> +	chan = handle->shadow_chan;
>  	*len = lib_ring_buffer_get_read_data_size(&chan->backend.config, buf,
>  		handle);
>  	*len = PAGE_ALIGN(*len);
> 
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> lttng-dev at lists.lttng.org
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com