Re: [RFC PATCH 1/4] jbd2: make jdb2_debug module parameter per device

[harshad shirwadkar <harshadshirwadkar@gmail.com>]

I wonder if we should retain the existing module param as well apart
from the new device specific logging switch? If that switch is
enabled, we'll get jbd2 logs for all the devices. Given that the old
jbd2_debug interface was a module param, I wonder somebody somewhere
might have infrastructure on top of that to enable debugging for jbd2?
And by removing this interface we may accidentally break them?

On Thu, Jan 21, 2021 at 10:48 PM Chunguang Xu <brookxu.cn@gmail.com> wrote:
>
> From: Chunguang Xu <brookxu@tencent.com>
>
> On a multi-disk machine, because jbd2's debugging switch is global,this
> confuses the logs of multiple disks. It is not easy to distinguish the
> logs of each disk and the amount of generated logs is very large. Or a
> separate debugging switch for each disk would be better, so that you
> can easily distinguish the logs of a certain disk.
>
> Signed-off-by: Chunguang Xu <brookxu@tencent.com>
> ---
>  fs/jbd2/journal.c     | 63 +++++++++++++++++++++++++++++++++++--------
>  fs/jbd2/transaction.c |  2 +-
>  include/linux/jbd2.h  |  7 +++++
>  3 files changed, 60 insertions(+), 12 deletions(-)
>
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 2dc944442802..ae147cc713c7 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -48,14 +48,6 @@
>  #include <linux/uaccess.h>
>  #include <asm/page.h>
>
> -#ifdef CONFIG_JBD2_DEBUG
> -ushort jbd2_journal_enable_debug __read_mostly;
> -EXPORT_SYMBOL(jbd2_journal_enable_debug);
> -
> -module_param_named(jbd2_debug, jbd2_journal_enable_debug, ushort, 0644);
> -MODULE_PARM_DESC(jbd2_debug, "Debugging level for jbd2");
> -#endif
> -
>  EXPORT_SYMBOL(jbd2_journal_extend);
>  EXPORT_SYMBOL(jbd2_journal_stop);
>  EXPORT_SYMBOL(jbd2_journal_lock_updates);
> @@ -101,13 +93,13 @@ EXPORT_SYMBOL(jbd2_inode_cache);
>  static int jbd2_journal_create_slab(size_t slab_size);
>
>  #ifdef CONFIG_JBD2_DEBUG
> -void __jbd2_debug(int level, const char *file, const char *func,
> +void jbd2_log(int level, journal_t *j, const char *file, const char *func,
>                   unsigned int line, const char *fmt, ...)
>  {
>         struct va_format vaf;
>         va_list args;
>
> -       if (level > jbd2_journal_enable_debug)
> +       if (!j || level > j->j_debug_level)
>                 return;
>         va_start(args, fmt);
>         vaf.fmt = fmt;
> @@ -115,7 +107,7 @@ void __jbd2_debug(int level, const char *file, const char *func,
>         printk(KERN_DEBUG "%s: (%s, %u): %pV", file, func, line, &vaf);
Now that you have journal_t passed to jbd2_log, it would also be good
to print the name of the device in this message. I think you can use
j->j_devname for that.

Thanks,
Harshad
>         va_end(args);
>  }
> -EXPORT_SYMBOL(__jbd2_debug);
> +EXPORT_SYMBOL(jbd2_log);
>  #endif
>
>  /* Checksumming functions */
> @@ -1257,6 +1249,48 @@ static int jbd2_seq_info_release(struct inode *inode, struct file *file)
>         return seq_release(inode, file);
>  }
>
> +#ifdef CONFIG_JBD2_DEBUG
> +static int jbd2_proc_debug_show(struct seq_file *m, void *v)
> +{
> +       journal_t *j = m->private;
> +
> +       seq_printf(m, "%d\n", j->j_debug_level);
> +       return 0;
> +}
> +
> +static int jbd2_proc_debug_open(struct inode *inode, struct file *file)
> +{
> +       journal_t *journal = PDE_DATA(inode);
> +
> +       return single_open(file, jbd2_proc_debug_show, journal);
> +}
> +
> +static ssize_t jbd2_proc_debug_write(struct file *file,
> +               const char __user *buffer, size_t count, loff_t *ppos)
> +{
> +       struct seq_file *seq = file->private_data;
> +       journal_t *j = seq->private;
> +       char c;
> +
> +       if (get_user(c, buffer))
> +               return -EFAULT;
> +
> +       if (c < '0' || c > '5')
> +               return -EINVAL;
> +
> +       j->j_debug_level = c - '0';
> +       return count;
> +}
> +
> +static const struct proc_ops jbd2_debug_proc_ops = {
> +       .proc_open      = jbd2_proc_debug_open,
> +       .proc_read      = seq_read,
> +       .proc_write     = jbd2_proc_debug_write,
> +       .proc_release   = single_release,
> +       .proc_lseek     = seq_lseek,
> +};
> +#endif
> +
>  static const struct proc_ops jbd2_info_proc_ops = {
>         .proc_open      = jbd2_seq_info_open,
>         .proc_read      = seq_read,
> @@ -1272,12 +1306,19 @@ static void jbd2_stats_proc_init(journal_t *journal)
>         if (journal->j_proc_entry) {
>                 proc_create_data("info", S_IRUGO, journal->j_proc_entry,
>                                  &jbd2_info_proc_ops, journal);
> +#ifdef CONFIG_JBD2_DEBUG
> +               proc_create_data("jbd2_debug", S_IRUGO, journal->j_proc_entry,
> +                                &jbd2_debug_proc_ops, journal);
> +#endif
>         }
>  }
>
>  static void jbd2_stats_proc_exit(journal_t *journal)
>  {
>         remove_proc_entry("info", journal->j_proc_entry);
> +#ifdef CONFIG_JBD2_DEBUG
> +       remove_proc_entry("jbd2_debug", journal->j_proc_entry);
> +#endif
>         remove_proc_entry(journal->j_devname, proc_jbd2_stats);
>  }
>
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 9396666b7314..f25c6ff16165 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -150,7 +150,7 @@ static inline void update_t_max_wait(transaction_t *transaction,
>                                      unsigned long ts)
>  {
>  #ifdef CONFIG_JBD2_DEBUG
> -       if (jbd2_journal_enable_debug &&
> +       if (transaction->t_journal->j_debug_level &&
>             time_after(transaction->t_start, ts)) {
>                 ts = jbd2_time_diff(ts, transaction->t_start);
>                 spin_lock(&transaction->t_handle_lock);
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 99d3cd051ac3..600a2ea8324a 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1211,6 +1211,13 @@ struct journal_s
>          */
>         struct transaction_stats_s j_stats;
>
> +#ifdef CONFIG_JBD2_DEBUG
> +       /**
> +        * @j_debug_level: debugging level for jbd2.
> +        */
> +       unsigned int j_debug_level;
> +#endif
> +
>         /**
>          * @j_failed_commit: Failed journal commit ID.
>          */
> --
> 2.30.0
>