A ring-buffer writer is an entity outside of the kernel (most likely a
firmware or a hypervisor) capable of writing events in a ring-buffer
following the same format as the tracefs ring-buffer.
To setup the ring-buffer on the kernel side, a description of the pages
(struct trace_page_desc) is necessary. A callback (get_reader_page) must
also be provided. It is called whenever it is done reading the previous
reader page.
It is expected from the writer to keep the meta-page updated.
Signed-off-by: Vincent Donnefort <vdonnef...@google.com>
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index fd35d4ec12e1..d78a33b3c96e 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -83,21 +83,24 @@ u64 ring_buffer_event_time_stamp(struct trace_buffer
*buffer,
void ring_buffer_discard_commit(struct trace_buffer *buffer,
struct ring_buffer_event *event);
+struct ring_buffer_writer;
+
/*
* size is in bytes for each per CPU buffer.
*/
struct trace_buffer *
-__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key
*key);
+__ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key
*key,
+ struct ring_buffer_writer *writer);
/*
* Because the ring buffer is generic, if other users of the ring buffer get
* traced by ftrace, it can produce lockdep warnings. We need to keep each
* ring buffer's lock class separate.
*/
-#define ring_buffer_alloc(size, flags) \
-({ \
- static struct lock_class_key __key; \
- __ring_buffer_alloc((size), (flags), &__key); \
+#define ring_buffer_alloc(size, flags) \
+({ \
+ static struct lock_class_key __key; \
+ __ring_buffer_alloc((size), (flags), &__key, NULL); \
})
typedef bool (*ring_buffer_cond_fn)(void *data);
@@ -228,4 +231,54 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
struct vm_area_struct *vma);
int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
+
+#define meta_pages_lost(__meta) \
+ ((__meta)->Reserved1)
+#define meta_pages_touched(__meta) \
+ ((__meta)->Reserved2)
+
+struct rb_page_desc {
+ int cpu;
+ int nr_page_va; /* exclude the meta page */
+ unsigned long meta_va;
+ unsigned long page_va[];
+};
+
+struct trace_page_desc {
+ int nr_cpus;
+ char __data[]; /* list of rb_page_desc */
+};
+
+static inline
+struct rb_page_desc *__next_rb_page_desc(struct rb_page_desc *pdesc)
+{
+ size_t len = struct_size(pdesc, page_va, pdesc->nr_page_va);
+
+ return (struct rb_page_desc *)((void *)pdesc + len);
+}
+
+static inline
+struct rb_page_desc *__first_rb_page_desc(struct trace_page_desc *trace_pdesc)
+{
+ return (struct rb_page_desc *)(&trace_pdesc->__data[0]);
+}
+
+#define for_each_rb_page_desc(__pdesc, __cpu, __trace_pdesc) \
+ for (__pdesc = __first_rb_page_desc(__trace_pdesc), __cpu = 0; \
+ __cpu < (__trace_pdesc)->nr_cpus; \
+ __cpu++, __pdesc = __next_rb_page_desc(__pdesc))
+
+struct ring_buffer_writer {
+ struct trace_page_desc *pdesc;
+ int (*get_reader_page)(int cpu);
+ int (*reset)(int cpu);
+};
+
+int ring_buffer_poll_writer(struct trace_buffer *buffer, int cpu);
+
+#define ring_buffer_reader(writer) \
+({ \
+ static struct lock_class_key __key; \
+ __ring_buffer_alloc(0, RB_FL_OVERWRITE, &__key, writer);\
+})
#endif /* _LINUX_RING_BUFFER_H */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7abe671effbf..b05b7a95e3f1 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -495,6 +495,8 @@ struct ring_buffer_per_cpu {
unsigned long *subbuf_ids; /* ID to subbuf VA */
struct trace_buffer_meta *meta_page;
+ struct ring_buffer_writer *writer;
+
/* ring buffer pages to update, > 0 to add, < 0 to remove */
long nr_pages_to_update;
struct list_head new_pages; /* new pages to add */
@@ -517,6 +519,8 @@ struct trace_buffer {
struct ring_buffer_per_cpu **buffers;
+ struct ring_buffer_writer *writer;
+
struct hlist_node node;
u64 (*clock)(void);
@@ -1555,6 +1559,42 @@ static int __rb_allocate_pages(struct
ring_buffer_per_cpu *cpu_buffer,
return -ENOMEM;
}
+static struct rb_page_desc *rb_page_desc(struct trace_page_desc *trace_pdesc,
+ int cpu)
+{
+ struct rb_page_desc *pdesc;
+ size_t len;
+ int i;
+
+ if (!trace_pdesc)
+ return NULL;
+
+ if (cpu >= trace_pdesc->nr_cpus)
+ return NULL;
+
+ pdesc = __first_rb_page_desc(trace_pdesc);
+ len = struct_size(pdesc, page_va, pdesc->nr_page_va);
+ pdesc += len * cpu;
+
+ if (pdesc->cpu == cpu)
+ return pdesc;
+
+ /* Missing CPUs, need to linear search */
+
+ for_each_rb_page_desc(pdesc, i, trace_pdesc) {
+ if (pdesc->cpu == cpu)
+ return pdesc;
+ }
+
+ return NULL;
+}
+
+static void *rb_page_desc_page(struct rb_page_desc *pdesc, int page_id)
+{
+ return page_id > pdesc->nr_page_va ? NULL : (void
*)pdesc->page_va[page_id];
+}
+
+
static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long nr_pages)
{
@@ -1614,6 +1654,31 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long
nr_pages, int cpu)
cpu_buffer->reader_page = bpage;
+ if (buffer->writer) {
+ struct rb_page_desc *pdesc =
rb_page_desc(buffer->writer->pdesc, cpu);
+
+ if (!pdesc)
+ goto fail_free_reader;
+
+ cpu_buffer->writer = buffer->writer;
+ cpu_buffer->meta_page = (struct trace_buffer_meta *)(void
*)pdesc->meta_va;
+ cpu_buffer->subbuf_ids = pdesc->page_va;
+ cpu_buffer->nr_pages = pdesc->nr_page_va - 1;
+ atomic_inc(&cpu_buffer->record_disabled);
+ atomic_inc(&cpu_buffer->resize_disabled);
+
+ bpage->page = rb_page_desc_page(pdesc,
+
cpu_buffer->meta_page->reader.id);
+ if (!bpage->page)
+ goto fail_free_reader;
+ /*
+ * The meta-page can only describe which of the ring-buffer page
+ * is the reader. There is no need to init the rest of the
+ * ring-buffer.
+ */
+ return cpu_buffer;
+ }
+
page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_COMP |
__GFP_ZERO,
cpu_buffer->buffer->subbuf_order);
if (!page)
@@ -1651,6 +1716,10 @@ static void rb_free_cpu_buffer(struct
ring_buffer_per_cpu *cpu_buffer)
irq_work_sync(&cpu_buffer->irq_work.work);
+ /* ring_buffers with writer set do not own the data pages */
+ if (cpu_buffer->writer)
+ cpu_buffer->reader_page->page = NULL;
+
free_buffer_page(cpu_buffer->reader_page);
if (head) {
@@ -1681,7 +1750,8 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu
*cpu_buffer)
* drop data when the tail hits the head.
*/
struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
- struct lock_class_key *key)
+ struct lock_class_key *key,
+ struct ring_buffer_writer *writer)
{
struct trace_buffer *buffer;
long nr_pages;
@@ -1709,6 +1779,11 @@ struct trace_buffer *__ring_buffer_alloc(unsigned long
size, unsigned flags,
buffer->flags = flags;
buffer->clock = trace_clock_local;
buffer->reader_lock_key = key;
+ if (writer) {
+ buffer->writer = writer;
+ /* The writer is external and never done by the kernel */
+ atomic_inc(&buffer->record_disabled);
+ }
init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
init_waitqueue_head(&buffer->irq_work.waiters);
@@ -4456,8 +4531,54 @@ rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
}
}
+static bool rb_read_writer_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ local_set(&cpu_buffer->entries,
READ_ONCE(cpu_buffer->meta_page->entries));
+ local_set(&cpu_buffer->overrun,
READ_ONCE(cpu_buffer->meta_page->overrun));
+ local_set(&cpu_buffer->pages_touched,
READ_ONCE(meta_pages_touched(cpu_buffer->meta_page)));
+ local_set(&cpu_buffer->pages_lost,
READ_ONCE(meta_pages_lost(cpu_buffer->meta_page)));
+ /*
+ * No need to get the "read" field, it can be tracked here as any
+ * reader will have to go through a rign_buffer_per_cpu.
+ */
+
+ return rb_num_of_entries(cpu_buffer);
+}
+
static struct buffer_page *
-rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
+__rb_get_reader_page_from_writer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ u32 prev_reader;
+
+ if (!rb_read_writer_meta_page(cpu_buffer))
+ return NULL;
+
+ /* More to read on the reader page */
+ if (cpu_buffer->reader_page->read <
rb_page_size(cpu_buffer->reader_page))
+ return cpu_buffer->reader_page;
+
+ prev_reader = cpu_buffer->meta_page->reader.id;
+
+ WARN_ON(cpu_buffer->writer->get_reader_page(cpu_buffer->cpu));
+ /* nr_pages doesn't include the reader page */
+ if (cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages) {
+ WARN_ON(1);
+ return NULL;
+ }
+
+ cpu_buffer->reader_page->page =
+ (void
*)cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id];
+ cpu_buffer->reader_page->read = 0;
+ cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
+ cpu_buffer->lost_events = cpu_buffer->meta_page->reader.lost_events;
+
+ WARN_ON(prev_reader == cpu_buffer->meta_page->reader.id);
+
+ return cpu_buffer->reader_page;
+}
+
+static struct buffer_page *
+__rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *reader = NULL;
unsigned long bsize = READ_ONCE(cpu_buffer->buffer->subbuf_size);
@@ -4624,6 +4745,13 @@ rb_get_reader_page(struct ring_buffer_per_cpu
*cpu_buffer)
return reader;
}
+static struct buffer_page *
+rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+ return cpu_buffer->writer ?
__rb_get_reader_page_from_writer(cpu_buffer) :
+ __rb_get_reader_page(cpu_buffer);
+}
+
static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_event *event;
@@ -5028,7 +5156,7 @@ ring_buffer_read_prepare(struct trace_buffer *buffer, int
cpu, gfp_t flags)
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_iter *iter;
- if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->writer)
return NULL;
iter = kzalloc(sizeof(*iter), flags);
@@ -5198,6 +5326,22 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *page;
+ if (cpu_buffer->writer) {
+ if (!cpu_buffer->writer->reset)
+ return;
+
+ cpu_buffer->writer->reset(cpu_buffer->cpu);
+ rb_read_writer_meta_page(cpu_buffer);
+
+ /* Read related values, not covered by the meta-page */
+ local_set(&cpu_buffer->pages_read, 0);
+ cpu_buffer->read = 0;
+ cpu_buffer->read_bytes = 0;
+ cpu_buffer->last_overrun = 0;
+
+ return;
+ }
+
rb_head_page_deactivate(cpu_buffer);
cpu_buffer->head_page
@@ -5428,6 +5572,49 @@ bool ring_buffer_empty_cpu(struct trace_buffer *buffer,
int cpu)
}
EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
+int ring_buffer_poll_writer(struct trace_buffer *buffer, int cpu)
+{
+ struct ring_buffer_per_cpu *cpu_buffer;
+ unsigned long flags;
+
+ if (cpu != RING_BUFFER_ALL_CPUS) {
+ if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ return -EINVAL;
+
+ cpu_buffer = buffer->buffers[cpu];
+
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+ if (rb_read_writer_meta_page(cpu_buffer))
+ rb_wakeups(buffer, cpu_buffer);
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+ return 0;
+ }
+
+ /*
+ * Make sure all the ring buffers are up to date before we start reading
+ * them.
+ */
+ for_each_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
+
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+ rb_read_writer_meta_page(buffer->buffers[cpu]);
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ }
+
+ for_each_buffer_cpu(buffer, cpu) {
+ cpu_buffer = buffer->buffers[cpu];
+
+ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+ if (rb_num_of_entries(cpu_buffer))
+ rb_wakeups(buffer, buffer->buffers[cpu]);
+ raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+ }
+
+ return 0;
+}
+
#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
/**
* ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
@@ -5679,6 +5866,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
unsigned int commit;
unsigned int read;
u64 save_timestamp;
+ bool force_memcpy;
int ret = -1;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
@@ -5716,6 +5904,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
/* Check if any events were dropped */
missed_events = cpu_buffer->lost_events;
+ force_memcpy = cpu_buffer->mapped || cpu_buffer->writer;
+
/*
* If this page has been partially read or
* if len is not big enough to read the rest of the page or
@@ -5725,7 +5915,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
*/
if (read || (len < (commit - read)) ||
cpu_buffer->reader_page == cpu_buffer->commit_page ||
- cpu_buffer->mapped) {
+ force_memcpy) {
struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
unsigned int rpos = read;
unsigned int pos = 0;
@@ -6278,7 +6468,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
unsigned long flags, *subbuf_ids;
int err = 0;
- if (!cpumask_test_cpu(cpu, buffer->cpumask))
+ if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->writer)
return -EINVAL;
cpu_buffer = buffer->buffers[cpu];
--
2.46.0.598.g6f2099f65c-goog
