Messages in this thread Patch in this message | | | From | John Keeping <> | Subject | [PATCH RESEND] tracing: make trace_marker{,_raw} stream-like | Date | Tue, 7 Dec 2021 14:25:58 +0000 |
| |
The tracing marker files are write-only streams with no meaningful concept of file position. Using stream_open() to mark them as stream-link indicates this and has the added advantage that a single file descriptor can now be used from multiple threads without contention thanks to clearing FMODE_ATOMIC_POS.
Note that this has the potential to break existing userspace by since both lseek(2) and pwrite(2) will now return ESPIPE when previously lseek would have updated the stored offset and pwrite would have appended to the trace. A survey of libtracefs and several other projects found to use trace_marker(_raw) [1][2][3] suggests that everyone limits themselves to calling write(2) and close(2) on these file descriptors so there is a good chance this will go unnoticed and the benefits of reduced overhead and lock contention seem worth the risk.
[1] https://github.com/google/perfetto [2] https://github.com/intel/media-driver/ [3] https://w1.fi/cgit/hostap/
Signed-off-by: John Keeping <john@metanate.com> --- Resending as requested at [1].
[1] https://lore.kernel.org/all/20211207090347.15822d87@gandalf.local.home/
kernel/trace/trace.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 88de94da596b1..7c91103ac1a04 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4834,6 +4834,12 @@ int tracing_open_generic_tr(struct inode *inode, struct file *filp) return 0; } +static int tracing_mark_open(struct inode *inode, struct file *filp) +{ + stream_open(inode, filp); + return tracing_open_generic_tr(inode, filp); +} + static int tracing_release(struct inode *inode, struct file *file) { struct trace_array *tr = inode->i_private; @@ -7110,9 +7116,6 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, if (tt) event_triggers_post_call(tr->trace_marker_file, tt); - if (written > 0) - *fpos += written; - return written; } @@ -7171,9 +7174,6 @@ tracing_mark_raw_write(struct file *filp, const char __user *ubuf, __buffer_unlock_commit(buffer, event); - if (written > 0) - *fpos += written; - return written; } @@ -7573,16 +7573,14 @@ static const struct file_operations tracing_free_buffer_fops = { }; static const struct file_operations tracing_mark_fops = { - .open = tracing_open_generic_tr, + .open = tracing_mark_open, .write = tracing_mark_write, - .llseek = generic_file_llseek, .release = tracing_release_generic_tr, }; static const struct file_operations tracing_mark_raw_fops = { - .open = tracing_open_generic_tr, + .open = tracing_mark_open, .write = tracing_mark_raw_write, - .llseek = generic_file_llseek, .release = tracing_release_generic_tr, }; -- 2.34.1
| |