On Wed, 12 Sep 2018 15:53:07 +0900 Sergey Senozhatsky <[email protected]> wrote:
> I scanned some of Linus' emails, and skimmed through previous discussions > on this topic. Let me quote Linus: > > : > : My preference as a user is actually to just have a dynamically > : re-sizable buffer (that's pretty much what I've done in *every* single > : user space project I've had in the last decade), but because some > : users might have atomicity issues I do suspect that we should just use > : a stack buffer. > : > : And then perhaps say that the buffer size has to be capped at 80 characters. > : > : Because if you're printing more than 80 characters and expecting it > : all to fit on a line, you're doing something else wrong anyway. > : > : And hide it not as a explicit "char buffer[80]]" allocation, but as a > : "struct line_buffer" or similar, so that > : > : (a) people don't get the line size wrong > : > : (b) the buffering code can add a few fields for length etc in there too > : > : Introduce a few helper functions for it: > : > : init_line_buffer(&buf); > : print_line(&buf, fmt, args); > : vprint_line(&buf, fmt, vararg); > : finish_line(&buf); > : This sounds like seq_buf to me. > > > > And this is, basically, what I have attached to this email. It's very > simple and very short. And I think this is what Linus wanted us to do. > > - usage example > > DEFINE_PR_LINE(KERN_ERR, pl); > > pr_line(&pl, "Hello, %s!\n", "buffer"); > pr_line(&pl, "%s", "OK.\n"); > pr_line(&pl, "Goodbye, %s", "buffer"); > pr_line(&pl, "\n"); > > dmesg | tail > > [ 69.908542] Hello, buffer! > [ 69.908544] OK. > [ 69.908545] Goodbye, buffer > > > - pr_cont-like usage > > DEFINE_PR_LINE(KERN_ERR, pl); > > pr_line(&pl,"%d ", 1); > pr_line(&pl,"%d ", 3); > pr_line(&pl,"%d ", 5); > pr_line(&pl,"%d ", 7); > pr_line(&pl,"%d\n", 9); > > dmesg | tail > > [ 69.908546] 1 3 5 7 9 > > > - An explicit, aux buffer // output should be truncated > > char buf[16]; > DEFINE_PR_LINE_BUF(KERN_ERR, ps, buf, sizeof(buf)); > > pr_line(&ps, "Test test test test test test test test test\n"); > pr_line(&ps, "\n"); > > > dmesg | tail > > [ 69.908547] Test test test ** truncated ** > > > Opinions? Will this work for us? > > ==== > > >From 7fd8407e0081d8979f08dec48e88364d6210b4ab Mon Sep 17 00:00:00 2001 > From: Sergey Senozhatsky <[email protected]> > Subject: [PATCH] printk: add pr_line buffering API > > Signed-off-by: Sergey Senozhatsky <[email protected]> > --- > include/linux/printk.h | 63 ++++++++++++++++++++++++++++++++++++++++++ > kernel/printk/printk.c | 55 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 118 insertions(+) > > diff --git a/include/linux/printk.h b/include/linux/printk.h > index cf3eccfe1543..fc5f11c7579c 100644 > --- a/include/linux/printk.h > +++ b/include/linux/printk.h > @@ -157,6 +157,15 @@ static inline void printk_nmi_direct_enter(void) { } > static inline void printk_nmi_direct_exit(void) { } > #endif /* PRINTK_NMI */ > > +#define PRINTK_PR_LINE_BUF_SZ 80 > + > +struct pr_line { > + char *buffer; > + int size; > + int len; > + char *level; > +}; Can you look at implementing this with using a seq_buf? -- Steve > + > #ifdef CONFIG_PRINTK > asmlinkage __printf(5, 0) > int vprintk_emit(int facility, int level, > @@ -209,6 +218,30 @@ extern asmlinkage void dump_stack(void) __cold; > extern void printk_safe_init(void); > extern void printk_safe_flush(void); > extern void printk_safe_flush_on_panic(void); > + > +#define DEFINE_PR_LINE(lev, name) \ > + char __pr_line_buf[PRINTK_PR_LINE_BUF_SZ]; \ > + struct pr_line name = { \ > + .buffer = __pr_line_buf, \ > + .size = PRINTK_PR_LINE_BUF_SZ, \ > + .len = 0, \ > + .level = lev, \ > + } > + > +#define DEFINE_PR_LINE_BUF(lev, name, buf, sz) \ > + struct pr_line name = { \ > + .buffer = buf, \ > + .size = (sz), \ > + .len = 0, \ > + .level = lev, \ > + } > + > +extern __printf(2, 3) > +int pr_line(struct pr_line *pl, const char *fmt, ...); > +extern __printf(2, 0) > +int vpr_line(struct pr_line *pl, const char *fmt, va_list args); > +extern void pr_line_flush(struct pr_line *pl); > + > #else > static inline __printf(1, 0) > int vprintk(const char *s, va_list args) > @@ -284,6 +317,36 @@ static inline void printk_safe_flush(void) > static inline void printk_safe_flush_on_panic(void) > { > } > + > +#define DEFINE_PR_LINE(lev, name) \ > + struct pr_line name = { \ > + .buffer = NULL, \ > + .size = 0, \ > + .len = 0, \ > + .level = lev, \ > + } > + > +#define DEFINE_PR_LINE_BUF(lev, name, buf, sz) \ > + struct pr_line name = { \ > + .buffer = buf, \ > + .size = 0, \ > + .len = 0, \ > + .level = lev, \ > + } > + > +static inline __printf(2, 3) > +int pr_line(struct pr_line *pl, const char *fmt, ...) > +{ > + return 0; > +} > +static inline __printf(2, 0) > +int vpr_line(struct pr_line *pl, const char *fmt, va_list args) > +{ > + return 0; > +} > +static inline void pr_line_flush(struct pr_line *pl) > +{ > +} > #endif > > extern int kptr_restrict; > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index fd6f8ed28e01..daeb41a57929 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2004,6 +2004,61 @@ asmlinkage __visible int printk(const char *fmt, ...) > } > EXPORT_SYMBOL(printk); > > +#define PR_LINE_TRUNCATED_MSG "** truncated **\n" > + > +int vpr_line(struct pr_line *pl, const char *fmt, va_list args) > +{ > + int len; > + > + if (unlikely(pl->size >= LOG_LINE_MAX)) > + pl->size = LOG_LINE_MAX - sizeof(PR_LINE_TRUNCATED_MSG); > + > + if (fmt[0] == '\n') { > + pr_line_flush(pl); > + return 0; > + } > + > + if (pl->len >= pl->size) > + return -1; > + > + len = vsnprintf(pl->buffer + pl->len, pl->size - pl->len, fmt, args); > + if (pl->len + len >= pl->size) { > + pl->len = pl->size + 1; > + return -1; > + } > + > + pl->len += len; > + if (pl->len && pl->buffer[pl->len - 1] == '\n') > + pr_line_flush(pl); > + return 0; > +} > +EXPORT_SYMBOL(vpr_line); > + > +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); > + > +void pr_line_flush(struct pr_line *pl) > +{ > + if (!pl->len) > + return; > + > + if (pl->len < pl->size) > + printk("%s%.*s", pl->level, pl->len, pl->buffer); > + else > + printk("%s%.*s%s", pl->level, pl->len, pl->buffer, > + PR_LINE_TRUNCATED_MSG); > + pl->len = 0; > +} > +EXPORT_SYMBOL(pr_line_flush); > #else /* CONFIG_PRINTK */ > > #define LOG_LINE_MAX 0
