Messages in this thread Patch in this message | | | Date | Mon, 10 Oct 2022 12:11:33 +0200 | From | Petr Mladek <> | Subject | Re: [PATCH printk 16/18] printk: Use struct cons_text_buf |
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On Sat 2022-09-24 02:10:52, John Ogness wrote: > From: Thomas Gleixner <tglx@linutronix.de> > > Replace the separately allocated output buffers with a single instance of > struct cons_text_buf. > > Note that the buffer size of devkmsg_user.text_buf, when replaced with > cons_text_buf.text, reduces from CONSOLE_EXT_LOG_MAX to CONSOLE_LOG_MAX. > However, the buffer is only used to read ringbuffer records, which have > a maximum size of LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX). > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: John Ogness <john.ogness@linutronix.de> > --- > kernel/printk/printk.c | 50 ++++++++++++++++++------------------------ > 1 file changed, 21 insertions(+), 29 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 65e9903d066f..9cbd44e9fc45 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -671,11 +671,9 @@ struct devkmsg_user { > atomic64_t seq; > struct ratelimit_state rs; > struct mutex lock; > - char buf[CONSOLE_EXT_LOG_MAX]; > - > struct printk_info info; > - char text_buf[CONSOLE_EXT_LOG_MAX]; > struct printk_record record; > + struct cons_text_buf txtbuf;
I think about how to make it more clear that @txtbuf is not a simple text buffer. It would help to better follow the code.
What about renaming "struct cons_text_buf", for example:
struct con_text_bufs; struct con_bufs; struct console_text_buffers; struct console_buffers;
and use the variables, for example:
ctbufs, cbufs, ct_bufs, c_bufs, con_bufs
> }; > > static __printf(3, 4) __cold > @@ -758,6 +756,8 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, > { > struct devkmsg_user *user = file->private_data; > struct printk_record *r = &user->record; > + char *outbuf = user->txtbuf.ext_text;
Please, use either "ext_text" or "ext_text_buf".
> + const int maxlen = sizeof(user->txtbuf.ext_text);
and "ext_text_size" or "ext_text_buf_size"
to follow the existing style, for example:
info_print_ext_header(buf, size, info). prb_rec_init_rd(r, info, text_buf, text_buf_size).
> size_t len; > ssize_t ret; > > @@ -2741,13 +2742,13 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ > goto skip; > } > > - if (ext_text) { > - write_text = ext_text; > - len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info); > - len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len, > + if (extmsg) {
We could get this from the console flags:
if (con->flags & CON_EXTENDED) {
> + write_text = txtbuf->ext_text; > + len = info_print_ext_header(write_text, CONSOLE_EXT_LOG_MAX, r.info); > + len += msg_print_ext_body(write_text + len, CONSOLE_EXT_LOG_MAX - len, > &r.text_buf[0], r.info->text_len, &r.info->dev_info);
I would use this opportunity and get rid of the hardcoded *_LOG_MAX lengts and something like:
write_text = txtbuf->ext_text; write_text_size = sizeof(txtbuf->ext_text); len = info_print_ext_header(write_text, write_text_size, r.info); len += msg_print_ext_body(write_text + len, write_text_size - len, &r.text_buf[0], r.info->text_len, &r.info->dev_info);
Using the hard coded size is error prone. It makes the review complicated especially when we are going to pass the buffers via some structures or generic pointers. I always have to check if it is still the same buffer.
The only sane way is to use either sizeof(buf) or pass/store @buf_size.
In addition, I would set here:
dropped_text = txtbuf->ext_text; dropped_text_size = sizeof(txtbuf->ext_text);
As a result, we could define as:
struct con_text_bufs { char ext_text[CONSOLE_EXT_LOG_MAX]; char text[CONSOLE_LOG_MAX]; } __no_randomize_layout;
and remove DROPPED_TEXT_MAX. I see that it is actually done later anyway. Adding the union is just a temporary twist that complicates the review.
> } else { > - write_text = text; > + write_text = txtbuf->text; > len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
write_text = txtbuf->text; write_text_size = sizeof(txtbuf->text); len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
dropped_text = NULL; dropped_text_size = 0;
> } > > @@ -2765,7 +2766,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ > console_lock_spinning_enable(); > > stop_critical_timings(); /* don't trace print latency */ > - call_console_driver(con, write_text, len, dropped_text); > + call_console_driver(con, write_text, len, extmsg ? NULL : txtbuf->dropped_text);
call_console_driver(con, write_text, len, dropped_text, dropped_text_size);
> start_critical_timings(); > > con->seq++;
Best Regards, Petr
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