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Message-ID: <20230409173923.1822455-1-vdonnefort@google.com>
Date: Sun, 9 Apr 2023 18:39:21 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: rostedt@...dmis.org, mhiramat@...nel.org,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Cc: kernel-team@...roid.com, Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH v3 0/2] Introducing trace buffer mapping by user-space
The tracing ring-buffers can be stored on disk or sent to network without any
copy via splice. However the later doesn't allow real time processing of the
traces. A solution is to give access to userspace to the ring-buffer pages
directly via a mapping. A piece of software can now become a reader of the
ring-buffer, and drive a consuming or non-consuming read in a similar fashion to
what trace and trace_pipe offer.
Attached to this cover letter an example of consuming read for a ring-buffer,
using libtracefs.
Vincent
v2 -> v3:
* Remove data page list (for non-consuming read)
** Implies removing order > 0 meta-page
* Add a new meta page field ->read
* Rename ring_buffer_meta_page_header into ring_buffer_meta_header
v1 -> v2:
* Hide data_pages from the userspace struct
* Fix META_PAGE_MAX_PAGES
* Support for order > 0 meta-page
* Add missing page->mapping.
Vincent Donnefort (2):
ring-buffer: Introducing ring-buffer mapping functions
tracing: Allow user-space mapping of the ring-buffer
include/linux/ring_buffer.h | 7 +
include/uapi/linux/trace_mmap.h | 26 +++
kernel/trace/ring_buffer.c | 302 +++++++++++++++++++++++++++++++-
kernel/trace/trace.c | 72 +++++++-
4 files changed, 400 insertions(+), 7 deletions(-)
create mode 100644 include/uapi/linux/trace_mmap.h
--
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <signal.h>
#include <errno.h>
#include <unistd.h>
#include <tracefs.h>
#include <kbuffer.h>
#include <event-parse.h>
#include <asm/types.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#define TRACE_MMAP_IOCTL_GET_READER_PAGE _IO('T', 0x1)
struct ring_buffer_meta_header {
__u64 entries;
__u64 overrun;
__u32 pages_touched;
__u32 meta_page_size;
__u32 nr_data_pages; /* Number of pages in the ring-buffer */
__u32 reader_page; /* Reader page ID, from 0 to nr_data_pages - 1 */
__u32 read; /* Number of bytes read on the current reader page */
};
/* Need to access private struct to save counters */
struct kbuffer {
unsigned long long timestamp;
long long lost_events;
unsigned long flags;
void *subbuffer;
void *data;
unsigned int index;
unsigned int curr;
unsigned int next;
unsigned int size;
unsigned int start;
unsigned int first;
unsigned int (*read_4)(void *ptr);
unsigned long long (*read_8)(void *ptr);
unsigned long long (*read_long)(struct kbuffer *kbuf, void *ptr);
int (*next_event)(struct kbuffer *kbuf);
};
static char *argv0;
static bool need_exit;
static char *get_this_name(void)
{
static char *this_name;
char *arg;
char *p;
if (this_name)
return this_name;
arg = argv0;
p = arg+strlen(arg);
while (p >= arg && *p != '/')
p--;
p++;
this_name = p;
return p;
}
static void __vdie(const char *fmt, va_list ap, int err)
{
int ret = errno;
char *p = get_this_name();
if (err && errno)
perror(p);
else
ret = -1;
fprintf(stderr, " ");
vfprintf(stderr, fmt, ap);
fprintf(stderr, "\n");
exit(ret);
}
void pdie(const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
__vdie(fmt, ap, 1);
va_end(ap);
}
static void read_page(struct tep_handle *tep, struct kbuffer *kbuf,
void *data, int page)
{
static struct trace_seq seq;
struct tep_record record;
if (seq.buffer)
trace_seq_reset(&seq);
else
trace_seq_init(&seq);
while ((record.data = kbuffer_read_event(kbuf, &record.ts))) {
kbuffer_next_event(kbuf, NULL);
tep_print_event(tep, &seq, &record,
"%s-%d %9d\t%s\n", TEP_PRINT_COMM,
TEP_PRINT_PID, TEP_PRINT_TIME, TEP_PRINT_NAME);
trace_seq_do_printf(&seq);
trace_seq_reset(&seq);
}
}
static int next_reader_page(int fd, struct ring_buffer_meta_header *meta,
struct kbuffer *kbuf)
{
int prev_reader_page = meta->reader_page;
if (ioctl(fd, TRACE_MMAP_IOCTL_GET_READER_PAGE) < 0)
pdie("ioctl");
return meta->reader_page;
}
static void signal_handler(int unused)
{
printf("Exit!\n");
need_exit = true;
}
int main(int argc, char **argv)
{
int page_size, meta_len, data_len, page, fd, start = -1;
unsigned long prev_read, prev_entries;
struct ring_buffer_meta_header *map;
unsigned long long prev_timestamp;
struct tep_handle *tep;
struct kbuffer *kbuf;
void *meta, *data;
char *buf, path[32];
int cpu;
if (argc != 2)
return -EINVAL;
argv0 = argv[0];
cpu = atoi(argv[1]);
snprintf(path, 32, "per_cpu/cpu%d/trace_pipe_raw", cpu);
tep = tracefs_local_events(NULL);
kbuf = tep_kbuffer(tep);
page_size = getpagesize();
fd = tracefs_instance_file_open(NULL, path, O_RDONLY);
if (fd < 0)
pdie("raw");
meta = mmap(NULL, page_size, PROT_READ, MAP_SHARED, fd, 0);
if (meta == MAP_FAILED)
pdie("mmap");
map = (struct ring_buffer_meta_header *)meta;
meta_len = map->meta_page_size;
printf("entries: %llu\n", map->entries);
printf("overrun: %llu\n", map->overrun);
printf("pages_touched: %u\n", map->pages_touched);
printf("reader_page: %u\n", map->reader_page);
printf("nr_data_pages: %u\n\n", map->nr_data_pages);
data_len = page_size * map->nr_data_pages;
data = mmap(NULL, data_len, PROT_READ, MAP_SHARED, fd, meta_len);
if (data == MAP_FAILED)
pdie("mmap data");
signal(SIGINT, signal_handler);
page = map->reader_page;
again:
prev_read = map->read;
do {
kbuffer_load_subbuffer(kbuf, data + page_size * page);
kbuf->curr = kbuf->index = kbuf->next = prev_read;
kbuffer_next_event(kbuf, NULL);
if (page != start)
printf("READER PAGE: %d\n", map->reader_page);
else
kbuf->timestamp = prev_timestamp;
start = page;
read_page(tep, kbuf, data, page);
} while ((page = next_reader_page(fd, meta, kbuf)) != start);
prev_timestamp = kbuf->timestamp;
prev_entries = map->entries;
while (prev_entries == *(volatile __u64 *)&map->entries && !need_exit)
usleep(100000);
if (!need_exit)
goto again;
munmap(data, data_len);
munmap(meta, page_size);
close(fd);
return 0;
}
--
2.40.0.577.gac1e443424-goog
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