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SubjectRe: [PATCH v2] dynamic_debug: allow to work if debugfs is disabled
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On 1/22/20 8:53 AM, Greg Kroah-Hartman wrote:
>
> With the realization that having debugfs enabled on "production" systems is
> generally not a good idea, debugfs is being disabled from more and more
> platforms over time. However, the functionality of dynamic debugging still is
> needed at times, and since it relies on debugfs for its user api, having
> debugfs disabled also forces dynamic debug to be disabled.
>
> To get around this, move the "control" file for dynamic_debug to procfs IFF
> debugfs is disabled. This lets people turn on debugging as needed at runtime
> for individual driverfs and subsystems.
>

Hi Greg,

Thanks for updating this. Just a comment below.


> Reported-by: many different companies
> Cc: Jason Baron <jbaron@akamai.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> v2: Fix up octal permissions and add procfs reference to the Kconfig
> entry, thanks to Will for the review.
>
> .../admin-guide/dynamic-debug-howto.rst | 3 +++
> lib/Kconfig.debug | 7 ++++---
> lib/dynamic_debug.c | 17 ++++++++++++++---
> 3 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/admin-guide/dynamic-debug-howto.rst b/Documentation/admin-guide/dynamic-debug-howto.rst
> index 252e5ef324e5..41f43a373a6a 100644
> --- a/Documentation/admin-guide/dynamic-debug-howto.rst
> +++ b/Documentation/admin-guide/dynamic-debug-howto.rst
> @@ -54,6 +54,9 @@ If you make a mistake with the syntax, the write will fail thus::
> <debugfs>/dynamic_debug/control
> -bash: echo: write error: Invalid argument
>
> +Note, for systems without 'debugfs' enabled, the control file can be
> +also found in ``/proc/dynamic_debug/control``.
> +
> Viewing Dynamic Debug Behaviour
> ===============================
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5ffe144c9794..49980eb8c18e 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -98,7 +98,7 @@ config DYNAMIC_DEBUG
> bool "Enable dynamic printk() support"
> default n
> depends on PRINTK
> - depends on DEBUG_FS
> + depends on (DEBUG_FS || PROC_FS)
> help
>
> Compiles debug level messages into the kernel, which would not
> @@ -116,8 +116,9 @@ config DYNAMIC_DEBUG
> Usage:
>
> Dynamic debugging is controlled via the 'dynamic_debug/control' file,
> - which is contained in the 'debugfs' filesystem. Thus, the debugfs
> - filesystem must first be mounted before making use of this feature.
> + which is contained in the 'debugfs' filesystem or procfs if
> + debugfs is not present. Thus, the debugfs or procfs filesystem
> + must first be mounted before making use of this feature.
> We refer the control file as: <debugfs>/dynamic_debug/control. This
> file contains a list of the debug statements that can be enabled. The
> format for each line of the file is:
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index c60409138e13..0f1b26f10fb2 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -993,13 +993,24 @@ static __initdata int ddebug_init_success;
>
> static int __init dynamic_debug_init_debugfs(void)
> {

The naming now is a little confusing - dynamic_debug_init_control ?


> - struct dentry *dir;
> + struct dentry *debugfs_dir;
> + struct proc_dir_entry *procfs_dir;
>
> if (!ddebug_init_success)
> return -ENODEV;
>
> - dir = debugfs_create_dir("dynamic_debug", NULL);
> - debugfs_create_file("control", 0644, dir, NULL, &ddebug_proc_fops);
> + /* Create the control file in debugfs if it is enabled */
> + if (debugfs_initialized) {
> + debugfs_dir = debugfs_create_dir("dynamic_debug", NULL);
> + debugfs_create_file("control", 0644, debugfs_dir, NULL,
> + &ddebug_proc_fops);
> + return 0;
> + }
> +
> + /* No debugfs so put it in procfs instead */
> + procfs_dir = proc_mkdir("dynamic_debug", NULL);
> + if (procfs_dir)
> + proc_create("control", 0644, procfs_dir, &ddebug_proc_fops);
>
> return 0;
> }
>

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