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SubjectRe: [PATCH] printk: inject caller information into the body of message
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On 2018/09/14 15:57, Sergey Senozhatsky wrote:
> On (09/13/18 23:28), Sergey Senozhatsky wrote:
>> Not that I see any problems with pr_line_flush(). But can drop it, sure.
>> pr_line() is a replacement for pr_cont() and as such it's not for multi-line
>> buffering.
>
> OK, attached.
> Let me know if anything needs to improved (including broken English).
> Will we keep in the printk tree or shall I send a formal patch to Andrew?



> @@ -20,6 +20,9 @@
> * Annotation for a "continued" line of log printout (only done after a
> * line that had no enclosing \n). Only to be used by core/arch code
> * during early bootup (a continued line is not SMP-safe otherwise).
> + *
> + * Please consider pr_line()/vpr_line() functions for SMP-safe continued
> + * line printing.

I think the advantage is not limited to SMP-safeness. Reducing the frequency of
calling printk() will reduce overhead. Also, latency for netconsole will be
reduced by sending a whole line in one printk().



> +/**
> + * DEFINE_PR_LINE - define a new pr_line variable
> + * @lev: printk() log level
> + * @name: variable name
> + *
> + * Defines a new pr_line varialbe, which would use an implicit

s/varialbe/variable/ .

> + * stack buffer of size __PR_LINE_BUF_SZ.
> + */
> +#define DEFINE_PR_LINE(lev, name) \
> + char __line_##name[__PR_LINE_BUF_SZ]; \
> + struct pr_line name = { \
> + .sb = __SEQ_BUF_INITIALIZER(__line_##name, \
> + __PR_LINE_BUF_SZ), \
> + .level = lev, \
> + }

Want a note that

static DEFINE_PR_LINE(lev, name);

won't make "name" variable "static" ?



> +/**
> + * DEFINE_PR_LINE_BUF - define a new pr_line variable
> + * @lev: printk() log level
> + * @name: variable name
> + * @buf: external buffer
> + * @sz: external buffer size
> + *
> + * Defines a new pr_line variable, which would use an external
> + * buffer for printk line.
> + */
> +#define DEFINE_PR_LINE_BUF(lev, name, buf, sz) \
> + struct pr_line name = { \
> + .sb = __SEQ_BUF_INITIALIZER(buf, (sz)), \
> + .level = lev, \
> + }
> +

I would use this one for the OOM killer. 80 bytes is too short.

static char oom_print_buf[1024];
DEFINE_PR_LINE_BUF(level, oom_print_buf);



> @@ -131,4 +187,8 @@ extern int
> seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
> #endif
>
> +extern __printf(2, 0)
> +int vpr_line(struct pr_line *pl, const char *fmt, va_list args);
> +extern __printf(2, 3)
> +int pr_line(struct pr_line *pl, const char *fmt, ...);

Do we want to mark "asmlinkage" like printk() ?

> @@ -324,3 +324,60 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
> s->readpos += cnt;
> return cnt;
> }
> +
> +/**
> + * vpr_line - Append data to the printk() line buffer
> + * @pl: the pr_line descriptor

s/descriptor/structure/ ?

> + * @fmt: printf format string
> + * @args: va_list of arguments from a printf() type function
> + *
> + * Writes a vnprintf() format into the printk() pr_line buffer.

s/vnprintf/vprintf/ ?

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