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    SubjectRe: [PATCH] printk: inject caller information into the body of message
    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?

    ===

    From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
    Subject: [PATCH] lib/seq_buf: add pr_line buffering API

    Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    ---
    include/linux/kern_levels.h | 3 ++
    include/linux/seq_buf.h | 60 +++++++++++++++++++++++++++++++++++++
    lib/seq_buf.c | 57 +++++++++++++++++++++++++++++++++++
    3 files changed, 120 insertions(+)

    diff --git a/include/linux/kern_levels.h b/include/linux/kern_levels.h
    index d237fe854ad9..9c281ac745b3 100644
    --- a/include/linux/kern_levels.h
    +++ b/include/linux/kern_levels.h
    @@ -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.
    */
    #define KERN_CONT KERN_SOH "c"

    diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
    index aa5deb041c25..b33aeea14803 100644
    --- a/include/linux/seq_buf.h
    +++ b/include/linux/seq_buf.h
    @@ -23,6 +23,62 @@ struct seq_buf {
    loff_t readpos;
    };

    +#define __SEQ_BUF_INITIALIZER(buf, length) \
    +{ \
    + .buffer = (buf), \
    + .size = (length), \
    + .len = 0, \
    + .readpos = 0, \
    +}
    +
    +#ifdef CONFIG_PRINTK
    +#define __PR_LINE_BUF_SZ 80
    +#else
    +#define __PR_LINE_BUF_SZ 0
    +#endif
    +
    +/**
    + * pr_line - printk() line buffer structure
    + * @sb: underlying seq buffer, which holds the data
    + * @level: printk() log level (KERN_ERR, etc.)
    + */
    +struct pr_line {
    + struct seq_buf sb;
    + char *level;
    +};
    +
    +/**
    + * 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
    + * 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, \
    + }
    +
    +/**
    + * 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, \
    + }
    +
    static inline void seq_buf_clear(struct seq_buf *s)
    {
    s->len = 0;
    @@ -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, ...);
    #endif /* _LINUX_SEQ_BUF_H */
    diff --git a/lib/seq_buf.c b/lib/seq_buf.c
    index 11f2ae0f9099..fada7623f168 100644
    --- a/lib/seq_buf.c
    +++ b/lib/seq_buf.c
    @@ -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
    + * @fmt: printf format string
    + * @args: va_list of arguments from a printf() type function
    + *
    + * Writes a vnprintf() format into the printk() pr_line buffer.
    + * Terminating new-line symbol flushes (prints) the buffer.
    + *
    + * Unlike pr_cont() and printk(KERN_CONT), this function is SMP-safe
    + * and shall be used for continued line printing.
    + *
    + * Returns zero on success, -1 on overflow.
    + */
    +int vpr_line(struct pr_line *pl, const char *fmt, va_list args)
    +{
    + struct seq_buf *s = &pl->sb;
    + int ret, len;
    +
    + ret = seq_buf_vprintf(s, fmt, args);
    +
    + len = seq_buf_used(s);
    + if (len && s->buffer[len - 1] == '\n') {
    + printk("%s%.*s", pl->level ? : KERN_DEFAULT, len, s->buffer);
    + seq_buf_clear(s);
    + }
    +
    + return ret;
    +}
    +EXPORT_SYMBOL(vpr_line);
    +
    +/**
    + * pr_line - Append data to the printk() line buffer
    + * @pl: the pr_line descriptor
    + * @fmt: printf format string
    + *
    + * Writes a printf() format into the printk() pr_line buffer.
    + * Terminating new-line symbol flushes (prints) the buffer.
    + *
    + * Unlike pr_cont() and printk(KERN_CONT), this function is SMP-safe
    + * and shall be used for continued line printing.
    + *
    + * Returns zero on success, -1 on overflow.
    + */
    +int pr_line(struct pr_line *pl, const char *fmt, ...)
    +{
    + va_list ap;
    + int ret;
    +
    + va_start(ap, fmt);
    + ret = vpr_line(pl, fmt, ap);
    + va_end(ap);
    +
    + return ret;
    +}
    +EXPORT_SYMBOL(pr_line);
    --
    2.19.0
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