Messages in this thread | | | Date | Fri, 28 Jul 2023 17:47:52 +0100 | Subject | [PATCH v5 0/2] Introducing trace buffer mapping by user-space | From | Vincent Donnefort <> |
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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
v4 -> v5: * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3)
v3 -> v4: * Add to the meta-page: - pages_lost / pages_read (allow to compute how full is the ring-buffer) - read (allow to compute how many entries can be read) - A reader_page struct. * Rename ring_buffer_meta_header -> ring_buffer_meta * Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page * Properly consume events on ring_buffer_map_get_reader_page() with rb_advance_reader().
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 | 28 +++ kernel/trace/ring_buffer.c | 321 +++++++++++++++++++++++++++++++- kernel/trace/trace.c | 72 ++++++- 4 files changed, 422 insertions(+), 6 deletions(-) create mode 100644 include/uapi/linux/trace_mmap.h
-- 2.41.0.487.g6d72f3e995-goog
#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)
/* 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); };
struct ring_buffer_meta { unsigned long entries; unsigned long overrun; unsigned long read;
unsigned long pages_touched; unsigned long pages_lost; unsigned long pages_read;
__u32 meta_page_size; __u32 nr_data_pages; /* Number of pages in the ring-buffer */
struct reader_page { __u32 id; /* Reader page ID from 0 to nr_data_pages - 1 */ __u32 read; /* Number of bytes read on the reader page */ unsigned long lost_events; /* Events lost at the time of the reader swap */ } reader_page; };
static char *argv0; static bool exit_requested;
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); }
#define READ_ONCE(x) (*(volatile typeof(x) *)&(x))
static unsigned long number_entries(struct ring_buffer_meta *meta) { return READ_ONCE(meta->entries) - (READ_ONCE(meta->overrun) + READ_ONCE(meta->read)); }
static void read_page(struct tep_handle *tep, struct kbuffer *kbuf) { 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 *meta, unsigned long *read) { __u32 prev_reader, new_reader; unsigned long prev_read;
prev_read = READ_ONCE(meta->reader_page.read); prev_reader = READ_ONCE(meta->reader_page.id); if (ioctl(fd, TRACE_MMAP_IOCTL_GET_READER_PAGE) < 0) pdie("ioctl"); new_reader = READ_ONCE(meta->reader_page.id);
if (prev_reader != new_reader) *read = 0; else *read = prev_read;
return new_reader; }
static void signal_handler(int unused) { printf("Exit!\n"); exit_requested = true; }
int main(int argc, char **argv) { int page_size, meta_len, data_len, page, fd; struct ring_buffer_meta *map; struct tep_handle *tep; struct kbuffer *kbuf; unsigned long read; void *meta, *data; char 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 *)meta; meta_len = map->meta_page_size;
printf("entries: %lu\n", map->entries); printf("overrun: %lu\n", map->overrun); printf("read: %lu\n", map->read); printf("pages_touched: %lu\n", map->pages_touched); printf("pages_lost: %lu\n", map->pages_lost); printf("pages_read: %lu\n", map->pages_read);
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);
while (!exit_requested) { if (!number_entries(map)) { usleep(100000); continue; }
page = next_reader_page(fd, map, &read); kbuffer_load_subbuffer(kbuf, data + page_size * page); while (kbuf->curr < read) kbuffer_next_event(kbuf, NULL);
read_page(tep, kbuf); }
munmap(data, data_len); munmap(meta, page_size); close(fd);
return 0; }
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