Messages in this thread | | | Date | Wed, 22 Mar 2023 10:22:42 +0000 | Subject | [PATCH v2 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
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 <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_page_header { __u64 entries; __u64 overrun; __u32 pages_touched; __u32 meta_page_size; __u32 reader_page; /* ID of the current reader page */ __u32 nr_data_pages; /* doesn't take into account the reader_page */ __u32 data_page_head; /* ring-buffer head as an offset from data_start */ __u32 data_start; /* offset within the meta 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_page_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; struct ring_buffer_meta_page_header *map; struct kbuffer *kbuf, prev_kbuf; struct tep_handle *tep; __u64 prev_entries; void *meta, *data; char *buf, path[32]; int cpu;
argv0 = argv[0]; cpu = atoi(argv[1]); snprintf(path, 32, "per_cpu/cpu%d/trace_pipe_raw", cpu);
signal(SIGINT, signal_handler); 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 = meta; meta_len = map->meta_page_size;
if (meta_len > page_size) { munmap(meta, page_size); meta = mmap(NULL, meta_len, PROT_READ, MAP_SHARED, fd, 0); if (meta == MAP_FAILED) pdie("mmap"); map = meta; }
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 + 1);
data = mmap(NULL, data_len, PROT_READ, MAP_SHARED, fd, meta_len); if (data == MAP_FAILED) pdie("mmap data");
page = ((struct ring_buffer_meta_page_header *)meta)->reader_page; again: do { kbuffer_load_subbuffer(kbuf, data + page_size * page);
if (page != start) { printf("READER PAGE: %d\n", map->reader_page); } else { kbuf->curr = prev_kbuf.curr; kbuf->index = prev_kbuf.index; kbuf->next = prev_kbuf.next; kbuf->timestamp = prev_kbuf.timestamp; kbuffer_next_event(kbuf, NULL); }
prev_entries = map->entries; start = page;
read_page(tep, kbuf, data, page); } while ((page = next_reader_page(fd, meta, kbuf)) != start);
prev_kbuf.curr = kbuf->curr; prev_kbuf.index = kbuf->index; prev_kbuf.next = kbuf->next; prev_kbuf.timestamp = kbuf->timestamp;
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; }
include/linux/ring_buffer.h | 8 + include/uapi/linux/trace_mmap.h | 28 +++ kernel/trace/ring_buffer.c | 384 +++++++++++++++++++++++++++++++- kernel/trace/trace.c | 76 ++++++- 4 files changed, 490 insertions(+), 6 deletions(-) create mode 100644 include/uapi/linux/trace_mmap.h
-- 2.40.0.rc1.284.g88254d51c5-goog
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