Commit 8789a9e7 authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar

ring-buffer: read page interface

Impact: new API to ring buffer

This patch adds a new interface into the ring buffer that allows a
page to be read from the ring buffer on a given CPU. For every page
read, one must also be given to allow for a "swap" of the pages.

 rpage = ring_buffer_alloc_read_page(buffer);
 if (!rpage)
	goto err;
 ret = ring_buffer_read_page(buffer, &rpage, cpu, full);
 if (!ret)
	goto empty;
 process_page(rpage);
 ring_buffer_free_read_page(rpage);

The caller of these functions must handle any waits that are
needed to wait for new data. The ring_buffer_read_page will simply
return 0 if there is no data, or if "full" is set and the writer
is still on the current page.
Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent abc9b56d
......@@ -124,6 +124,11 @@ void tracing_on(void);
void tracing_off(void);
void tracing_off_permanent(void);
void *ring_buffer_alloc_read_page(struct ring_buffer *buffer);
void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data);
int ring_buffer_read_page(struct ring_buffer *buffer,
void **data_page, int cpu, int full);
enum ring_buffer_flags {
RB_FL_OVERWRITE = 1 << 0,
};
......
......@@ -687,6 +687,12 @@ static inline int rb_null_event(struct ring_buffer_event *event)
return event->type == RINGBUF_TYPE_PADDING;
}
static inline void *
__rb_data_page_index(struct buffer_data_page *page, unsigned index)
{
return page->data + index;
}
static inline void *__rb_page_index(struct buffer_page *page, unsigned index)
{
return page->page->data + index;
......@@ -2232,6 +2238,166 @@ int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
return 0;
}
static void rb_remove_entries(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_data_page *page)
{
struct ring_buffer_event *event;
unsigned long head;
__raw_spin_lock(&cpu_buffer->lock);
for (head = 0; head < local_read(&page->commit);
head += rb_event_length(event)) {
event = __rb_data_page_index(page, head);
if (RB_WARN_ON(cpu_buffer, rb_null_event(event)))
return;
/* Only count data entries */
if (event->type != RINGBUF_TYPE_DATA)
continue;
cpu_buffer->entries--;
}
__raw_spin_unlock(&cpu_buffer->lock);
}
/**
* ring_buffer_alloc_read_page - allocate a page to read from buffer
* @buffer: the buffer to allocate for.
*
* This function is used in conjunction with ring_buffer_read_page.
* When reading a full page from the ring buffer, these functions
* can be used to speed up the process. The calling function should
* allocate a few pages first with this function. Then when it
* needs to get pages from the ring buffer, it passes the result
* of this function into ring_buffer_read_page, which will swap
* the page that was allocated, with the read page of the buffer.
*
* Returns:
* The page allocated, or NULL on error.
*/
void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
{
unsigned long addr;
struct buffer_data_page *page;
addr = __get_free_page(GFP_KERNEL);
if (!addr)
return NULL;
page = (void *)addr;
return page;
}
/**
* ring_buffer_free_read_page - free an allocated read page
* @buffer: the buffer the page was allocate for
* @data: the page to free
*
* Free a page allocated from ring_buffer_alloc_read_page.
*/
void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
{
free_page((unsigned long)data);
}
/**
* ring_buffer_read_page - extract a page from the ring buffer
* @buffer: buffer to extract from
* @data_page: the page to use allocated from ring_buffer_alloc_read_page
* @cpu: the cpu of the buffer to extract
* @full: should the extraction only happen when the page is full.
*
* This function will pull out a page from the ring buffer and consume it.
* @data_page must be the address of the variable that was returned
* from ring_buffer_alloc_read_page. This is because the page might be used
* to swap with a page in the ring buffer.
*
* for example:
* rpage = ring_buffer_alloc_page(buffer);
* if (!rpage)
* return error;
* ret = ring_buffer_read_page(buffer, &rpage, cpu, 0);
* if (ret)
* process_page(rpage);
*
* When @full is set, the function will not return true unless
* the writer is off the reader page.
*
* Note: it is up to the calling functions to handle sleeps and wakeups.
* The ring buffer can be used anywhere in the kernel and can not
* blindly call wake_up. The layer that uses the ring buffer must be
* responsible for that.
*
* Returns:
* 1 if data has been transferred
* 0 if no data has been transferred.
*/
int ring_buffer_read_page(struct ring_buffer *buffer,
void **data_page, int cpu, int full)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
struct buffer_data_page *page;
unsigned long flags;
int ret = 0;
if (!data_page)
return 0;
page = *data_page;
if (!page)
return 0;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
/*
* rb_buffer_peek will get the next ring buffer if
* the current reader page is empty.
*/
event = rb_buffer_peek(buffer, cpu, NULL);
if (!event)
goto out;
/* check for data */
if (!local_read(&cpu_buffer->reader_page->page->commit))
goto out;
/*
* If the writer is already off of the read page, then simply
* switch the read page with the given page. Otherwise
* we need to copy the data from the reader to the writer.
*/
if (cpu_buffer->reader_page == cpu_buffer->commit_page) {
unsigned int read = cpu_buffer->reader_page->read;
if (full)
goto out;
/* The writer is still on the reader page, we must copy */
page = cpu_buffer->reader_page->page;
memcpy(page->data,
cpu_buffer->reader_page->page->data + read,
local_read(&page->commit) - read);
/* consume what was read */
cpu_buffer->reader_page += read;
} else {
/* swap the pages */
rb_init_page(page);
page = cpu_buffer->reader_page->page;
cpu_buffer->reader_page->page = *data_page;
cpu_buffer->reader_page->read = 0;
*data_page = page;
}
ret = 1;
/* update the entry counter */
rb_remove_entries(cpu_buffer, page);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return ret;
}
static ssize_t
rb_simple_read(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
......
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