Re: [RFC 3/8] kmsg: introduce additional kmsg devices support

Petr Mladek
2015-07-08T11:11:10Z

On Fri 2015-07-03 12:49:50, Marcin Niesluchowski wrote:
> kmsg device provides operations on cyclic logging buffer used mainly
> by kernel but also in userspace by privileged processes.
>
> Additional kmsg devices keep the same log format but may be added
> dynamically with custom size.
>
> Signed-off-by: Marcin Niesluchowski <m.niesluchow@samsung.com>

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -234,29 +234,37 @@ struct printk_log {
> u8 level:3; /* syslog level */
> };

Just in case, this is accepted. If you already touch the API, I would
suggest to rename struct printk_log to printk_msg. The current name
is pretty misleading.

> +struct log_buffer {
> +#ifdef CONFIG_PRINTK
> + struct list_head list; /* kmsg as head of the list */
> + char *buf; /* cyclic log buffer */
> + u32 len; /* buffer length */
> + wait_queue_head_t wait; /* wait queue for kmsg buffer */
> +#endif
> /*
> - * The logbuf_lock protects kmsg buffer, indices, counters. This can be taken
> - * within the scheduler's rq lock. It must be released before calling
> - * console_unlock() or anything else that might wake up a process.
> + * The lock protects kmsg buffer, indices, counters. This can be taken within
> + * the scheduler's rq lock. It must be released before calling console_unlock()
> + * or anything else that might wake up a process.
> */
> -static DEFINE_RAW_SPINLOCK(logbuf_lock);
> + raw_spinlock_t lock;
> + u64 first_seq; /* sequence number of the first record stored */
> + u32 first_idx; /* index of the first record stored */
> +/* sequence number of the next record to store */
> + u64 next_seq;
> +#ifdef CONFIG_PRINTK
> + u32 next_idx; /* index of the next record to store */
> + int mode; /* mode of device (kmsg_sys only) */
> + int minor; /* minor representing buffer device */
> +#endif
> +};

> @@ -1069,10 +1253,10 @@ const struct file_operations kmsg_fops = {
> */
> void log_buf_kexec_setup(void)
> {
> - VMCOREINFO_SYMBOL(log_buf);
> - VMCOREINFO_SYMBOL(log_buf_len);
> - VMCOREINFO_SYMBOL(log_first_idx);
> - VMCOREINFO_SYMBOL(log_next_idx);
> + VMCOREINFO_SYMBOL(log_buf.buf);
> + VMCOREINFO_SYMBOL(log_buf.len);
> + VMCOREINFO_SYMBOL(log_buf.first_idx);
> + VMCOREINFO_SYMBOL(log_buf.next_idx);

Have you tried to use this in crash or some other utility, please?
I guess that it will need to be exported a similar way like
struct printk_log, something like:

VMCOREINFO_SYMBOL(log_buf);
VMCOREINFO_STRUCT_SIZE(log_buffer);
VMCOREINFO_OFFSET(log_buffer, buf);
VMCOREINFO_OFFSET(log_buffer, len);
VMCOREINFO_OFFSET(log_buffer, first_idx);
VMCOREINFO_OFFSET(log_buffer, next_idx);

Best Regards,
Petr