[ltt-dev] [PATCH take2 04/13] read C-style string from ltt-relay buffer

[Mathieu Desnoyers]

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> C-style string which is written to ltt-relay buffer is not in
> continuous memory region, we implement ltt_relay_read_cstr()
> read it.
> 
> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> ---
> diff --git a/include/linux/ltt-relay.h b/include/linux/ltt-relay.h
> index 1225a6a..437b2d9 100644
> --- a/include/linux/ltt-relay.h
> +++ b/include/linux/ltt-relay.h
> @@ -146,6 +146,9 @@ extern int ltt_relay_write(struct rchan_buf *buf, size_t offset,
>  extern int ltt_relay_read(struct rchan_buf *buf, size_t offset,
>  	void *dest, size_t len);
>  
> +extern int ltt_relay_read_cstr(struct rchan_buf *buf, size_t offset,
> +	void *dest, size_t len);
> +
>  extern struct buf_page *ltt_relay_read_get_page(struct rchan_buf *buf,
>  	size_t offset);
>  
> diff --git a/ltt/ltt-relay-alloc.c b/ltt/ltt-relay-alloc.c
> index e15f244..4b8e4c3 100644
> --- a/ltt/ltt-relay-alloc.c
> +++ b/ltt/ltt-relay-alloc.c
> @@ -614,6 +614,50 @@ int ltt_relay_read(struct rchan_buf *buf, size_t offset,
>  EXPORT_SYMBOL_GPL(ltt_relay_read);
>  
>  /**
> + * ltt_relay_read_cstr - read a C-style string from ltt_relay_buffer.
> + * @buf : buffer
> + * @offset : offset within the buffer
> + * @dest : destination address
> + * @len : destination's length
> + *
> + * return string's length
> + */
> +int ltt_relay_read_cstr(struct rchan_buf *buf, size_t offset,
> +		void *dest, size_t len)
> +{
> +	struct buf_page *page;
> +	ssize_t pagecpy, pagelen, strpagelen, orig_offset = offset;
> +	char *str;
> +
> +	offset &= buf->chan->alloc_size - 1;

if orig_offset is >= buf->chan->alloc_size, this mask will make
the return offset - orig_offset; return a huge value. It's not expected
isn't it ?

That should be :

offset &= buf->chan->alloc_size - 1;
orig_offset = offset;

instead. This assumes the read will never cross subbuffers, which is
ensured by the WARN_ON below.

Mathieu

> +	page = buf->rpage;
> +	for (;;) {
> +		page = ltt_relay_cache_page(buf, &buf->rpage, page, offset);
> +		str = (char *)page_address(page->page) + (offset & ~PAGE_MASK);
> +		pagelen = PAGE_SIZE - (offset & ~PAGE_MASK);
> +		strpagelen = strnlen(str, pagelen);
> +		if (len) {
> +			pagecpy = min_t(size_t, len, strpagelen);
> +			memcpy(dest, str, pagecpy);
> +			len -= pagecpy;
> +			dest += pagecpy;
> +		}
> +		offset += strpagelen;
> +		if (strpagelen < pagelen)
> +			break;
> +		/*
> +		 * Underlying layer should never ask for reads across
> +		 * subbuffers.
> +		 */
> +		WARN_ON(offset >= buf->chan->alloc_size);
> +	}
> +	if (len)
> +		((char *)dest)[0] = 0;
> +	return offset - orig_offset;
> +}
> +EXPORT_SYMBOL_GPL(ltt_relay_read_cstr);
> +
> +/**
>   * ltt_relay_read_get_page - Get a whole page to read from
>   * @buf : buffer
>   * @offset : offset within the buffer
> 
> 
> 
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> 

-- 
Mathieu Desnoyers
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