On (11/02/18 22:31), Tetsuo Handa wrote:
> (1) Call get_printk_buffer() and acquire "struct printk_buffer *".
>
> (2) Rewrite printk() calls in the following way. The "ptr" is
> "struct printk_buffer *" obtained in step (1).
>
> printk(fmt, ...) => printk_buffered(ptr, fmt, ...)
> vprintk(fmt, args) => vprintk_buffered(ptr, fmt, args)
> pr_emerg(fmt, ...) => bpr_emerg(ptr, fmt, ...)
> pr_alert(fmt, ...) => bpr_alert(ptr, fmt, ...)
> pr_crit(fmt, ...) => bpr_crit(ptr, fmt, ...)
> pr_err(fmt, ...) => bpr_err(ptr, fmt, ...)
> pr_warning(fmt, ...) => bpr_warning(ptr, fmt, ...)
> pr_warn(fmt, ...) => bpr_warn(ptr, fmt, ...)
> pr_notice(fmt, ...) => bpr_notice(ptr, fmt, ...)
> pr_info(fmt, ...) => bpr_info(ptr, fmt, ...)
> pr_cont(fmt, ...) => bpr_cont(ptr, fmt, ...)
>
> (3) Release "struct printk_buffer" by calling put_printk_buffer().
[..]
> Since we want to remove "struct cont" eventually, we will try to remove
> both "implicit printk() users who are expecting KERN_CONT behavior" and
> "explicit pr_cont()/printk(KERN_CONT) users". Therefore, converting to
> this API is recommended.
- The printk-fallback sounds like a hint that the existing 'cont' handling
better stay in the kernel. I don't see how the existing 'cont' is
significantly worse than
bpr_warn(NULL, ...)->printk() // no 'cont' support
I don't see why would we want to do it, sorry. I don't see "it takes 16
printk-buffers to make a thing go right" as a sure thing.
A question.
How bad would it actually be to:
- Allocate seq_buf 512-bytes buffer (GFP_ATOMIC) just-in-time, when we
need it.
// How often systems cannot allocate a 512-byte buffer? //
- OK, assuming that systems around the world are so badly OOM like all the
time and even kmalloc(512) is absolutely impossible, then have a fallback
to the existing 'cont' handling; it just looks to me better than a plain
printk()-fallback with removed 'cont' support.
- Do not allocate seq_buf if we are in printk-safe or in printk-nmi mode.
To avoid "buffering for the sake of buffering". IOW, when in printk-safe
use printk-safe.
-ss
