[PATCH v2 0/7] tracing/user_events: Update user_events ABI from

Beau Belgrave
2022-04-25T18:46:50Z

This series covers the changes that were brought up once user_events went into
5.18. The largest change is moving away from byte index to a bit index, as
first suggested by Mathieu Desnoyers.

The other changes are either fixes that have accumulated or found by Mathieu.

NOTE: The sample and self-tests do not build unless you manually install
user_events.h into usr/include/linux.

Link:
https://lore.kernel.org/all/2059213643.196683.1648499088753.JavaMail.zimbra@efficios.com/

Psuedo code example of typical usage with the new ABI:
struct user_reg reg;

int page_fd = open("user_events_status", O_RDWR);
char *page_data = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, page_fd,
0);
close(page_fd);

int data_fd = open("user_events_data", O_RDWR);

reg.size = sizeof(reg);
reg.name_args = (__u64)"test";

ioctl(data_fd, DIAG_IOCSREG, &reg);
int status_id = reg.status_bit / 8;
int status_mask = 1 << (reg.status_bit % 8);
int write_id = reg.write_index;

struct iovec io[2];
io[0].iov_base = &write_id;
io[0].iov_len = sizeof(write_id);
io[1].iov_base = payload;
io[1].iov_len = sizeof(payload);

if (page_data[status_id] & status_mask)
writev(data_fd, io, 2);

V2 Updates:
Changed from status_index and status_mask on user_reg to just status_bit.
Updated and added byte-wise and long-wise indexing pattern into docs.
Updated tests to use byte-wise index pattern.
Updated sample to show long-wise index pattern.

Beau Belgrave (7):
tracing/user_events: Fix repeated word in comments
tracing/user_events: Use NULL for strstr checks
tracing/user_events: Use WRITE instead of READ for io vector import
tracing/user_events: Ensure user provided strings are safely formatted
tracing/user_events: Use refcount instead of atomic for ref tracking
tracing/user_events: Use bits vs bytes for enabled status page data
tracing/user_events: Update ABI documentation to align to bits vs
bytes

Documentation/trace/user_events.rst | 86 ++++---
include/linux/user_events.h | 15 +-
kernel/trace/trace_events_user.c | 212 ++++++++++++------
samples/user_events/example.c | 25 ++-
.../selftests/user_events/ftrace_test.c | 47 +++-
.../testing/selftests/user_events/perf_test.c | 11 +-
6 files changed, 264 insertions(+), 132 deletions(-)

base-commit: 5cfff569cab8bf544bab62c911c5d6efd5af5e05
--
2.25.1