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Date: Thu, 1 Aug 2013 23:24:05 +0200
From: Jan Kara <jack@...e.cz>
To: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] jbd: use module parameters instead of debugfs for
jbd_debug
On Thu 01-08-13 15:01:05, Paul Gortmaker wrote:
> This is a direct backport of commit b6e96d0067d81f6a300bedee
> ("jbd2: use module parameters instead of debugfs for jbd_debug")
> from jbd2 into jbd. The value is in making ext4 and ext3 user
> experiences consistent with each other. Quoting the original:
>
> --------------
> There are multiple reasons to move away from debugfs. First of all,
> we are only using it for a single parameter, and it is much more
> complicated to set up (some 30 lines of code compared to 3), and one
> more thing that might fail while loading the jbd2 module.
>
> Secondly, as a module paramter it can be specified as a boot option if
> jbd2 is built into the kernel, or as a parameter when the module is
> loaded, and it can also be manipulated dynamically under
> /sys/module/jbd2/parameters/jbd2_debug. So it is more flexible.
>
> Ultimately we want to move away from using jbd_debug() towards
> tracepoints, but for now this is still a useful simplification of the
> code base.
> --------------
>
> It is worth noting that we use /sys/module/jbd/parameters/jbd1_debug
> (i.e. the "1" might appear odd) for the module parameter in order to
> avoid namespace collisions with the existing jbd_debug used as a
> function call.
>
> In addition, we combine the content of jbd2 commit 75497d0607b56e16e4
> ("jbd2: remove debug dependency on debug_fs and update Kconfig help text")
> since they were only separate commits unintentionally in jbd2.
Thanks for the patch but is jbd_debug really worth it - especially with
the somewhat ugly jbd1_debug? I don't thing anybody besides kernel
developers really uses it and those can figure how to do what they need...
Honza
>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> ---
> fs/jbd/Kconfig | 6 +++---
> fs/jbd/journal.c | 49 ++++++++-----------------------------------------
> include/linux/jbd.h | 3 +--
> 3 files changed, 12 insertions(+), 46 deletions(-)
>
> diff --git a/fs/jbd/Kconfig b/fs/jbd/Kconfig
> index 4e28bee..54cbb55 100644
> --- a/fs/jbd/Kconfig
> +++ b/fs/jbd/Kconfig
> @@ -15,7 +15,7 @@ config JBD
>
> config JBD_DEBUG
> bool "JBD (ext3) debugging support"
> - depends on JBD && DEBUG_FS
> + depends on JBD
> help
> If you are using the ext3 journaled file system (or potentially any
> other file system/device using JBD), this option allows you to
> @@ -24,7 +24,7 @@ config JBD_DEBUG
> debugging output will be turned off.
>
> If you select Y here, then you will be able to turn on debugging
> - with "echo N > /sys/kernel/debug/jbd/jbd-debug", where N is a
> + with "echo N > /sys/module/jbd/parameters/jbd1_debug", where N is a
> number between 1 and 5, the higher the number, the more debugging
> output is generated. To turn debugging off again, do
> - "echo 0 > /sys/kernel/debug/jbd/jbd-debug".
> + "echo 0 > /sys/module/jbd/parameters/jbd1_debug".
> diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
> index 6510d63..166263d 100644
> --- a/fs/jbd/journal.c
> +++ b/fs/jbd/journal.c
> @@ -35,7 +35,6 @@
> #include <linux/kthread.h>
> #include <linux/poison.h>
> #include <linux/proc_fs.h>
> -#include <linux/debugfs.h>
> #include <linux/ratelimit.h>
>
> #define CREATE_TRACE_POINTS
> @@ -44,6 +43,14 @@
> #include <asm/uaccess.h>
> #include <asm/page.h>
>
> +#ifdef CONFIG_JBD_DEBUG
> +ushort jbd_journal_enable_debug __read_mostly;
> +EXPORT_SYMBOL(jbd_journal_enable_debug);
> +
> +module_param_named(jbd1_debug, jbd_journal_enable_debug, ushort, 0644);
> +MODULE_PARM_DESC(jbd1_debug, "Debugging level for jbd");
> +#endif
> +
> EXPORT_SYMBOL(journal_start);
> EXPORT_SYMBOL(journal_restart);
> EXPORT_SYMBOL(journal_extend);
> @@ -2017,44 +2024,6 @@ void journal_put_journal_head(struct journal_head *jh)
> jbd_unlock_bh_journal_head(bh);
> }
>
> -/*
> - * debugfs tunables
> - */
> -#ifdef CONFIG_JBD_DEBUG
> -
> -u8 journal_enable_debug __read_mostly;
> -EXPORT_SYMBOL(journal_enable_debug);
> -
> -static struct dentry *jbd_debugfs_dir;
> -static struct dentry *jbd_debug;
> -
> -static void __init jbd_create_debugfs_entry(void)
> -{
> - jbd_debugfs_dir = debugfs_create_dir("jbd", NULL);
> - if (jbd_debugfs_dir)
> - jbd_debug = debugfs_create_u8("jbd-debug", S_IRUGO | S_IWUSR,
> - jbd_debugfs_dir,
> - &journal_enable_debug);
> -}
> -
> -static void __exit jbd_remove_debugfs_entry(void)
> -{
> - debugfs_remove(jbd_debug);
> - debugfs_remove(jbd_debugfs_dir);
> -}
> -
> -#else
> -
> -static inline void jbd_create_debugfs_entry(void)
> -{
> -}
> -
> -static inline void jbd_remove_debugfs_entry(void)
> -{
> -}
> -
> -#endif
> -
> struct kmem_cache *jbd_handle_cache;
>
> static int __init journal_init_handle_cache(void)
> @@ -2109,7 +2078,6 @@ static int __init journal_init(void)
> ret = journal_init_caches();
> if (ret != 0)
> journal_destroy_caches();
> - jbd_create_debugfs_entry();
> return ret;
> }
>
> @@ -2120,7 +2088,6 @@ static void __exit journal_exit(void)
> if (n)
> printk(KERN_EMERG "JBD: leaked %d journal_heads!\n", n);
> #endif
> - jbd_remove_debugfs_entry();
> journal_destroy_caches();
> }
>
> diff --git a/include/linux/jbd.h b/include/linux/jbd.h
> index 8685d1b..e45b430 100644
> --- a/include/linux/jbd.h
> +++ b/include/linux/jbd.h
> @@ -20,7 +20,6 @@
> #ifndef __KERNEL__
> #include "jfs_compat.h"
> #define JFS_DEBUG
> -#define jfs_debug jbd_debug
> #else
>
> #include <linux/types.h>
> @@ -55,7 +54,7 @@
> * CONFIG_JBD_DEBUG is on.
> */
> #define JBD_EXPENSIVE_CHECKING
> -extern u8 journal_enable_debug;
> +extern ushort journal_enable_debug;
>
> #define jbd_debug(n, f, a...) \
> do { \
> --
> 1.8.1.2
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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