lkml.org 
[lkml]   [2021]   [Mar]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 1/7] CMDLINE: add generic builtin command line
From
Date


Le 09/03/2021 à 01:02, Daniel Walker a écrit :
> This code allows architectures to use a generic builtin command line.
> The state of the builtin command line options across architecture is
> diverse. On x86 and mips they have pretty much the same code and the
> code prepends the builtin command line onto the boot loader provided
> one. On powerpc there is only a builtin override and nothing else.

Same comment as in v1: The above is not correct for powerpc.

>
> The code in this commit unifies the code into a generic
> header file under the CONFIG_GENERIC_CMDLINE option. When this
> option is enabled the architecture can call the cmdline_add_builtin()
> to add the builtin command line.
>
> Cc: xe-linux-external@cisco.com
> Signed-off-by: Ruslan Bilovol <rbilovol@cisco.com>
> Signed-off-by: Daniel Walker <danielwa@cisco.com>
> ---
> include/linux/cmdline.h | 89 +++++++++++++++++++++++++++++++++++++++++
> init/Kconfig | 68 +++++++++++++++++++++++++++++++
> 2 files changed, 157 insertions(+)
> create mode 100644 include/linux/cmdline.h
>
> diff --git a/include/linux/cmdline.h b/include/linux/cmdline.h
> new file mode 100644
> index 000000000000..00929b6e49e6
> --- /dev/null
> +++ b/include/linux/cmdline.h
> @@ -0,0 +1,89 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_CMDLINE_H
> +#define _LINUX_CMDLINE_H
> +
> +/*
> + *
> + * Copyright (C) 2006,2021. Cisco Systems, Inc.
> + *
> + * Generic Append/Prepend cmdline support.
> + */
> +
> +#if defined(CONFIG_GENERIC_CMDLINE) && defined(CONFIG_CMDLINE_BOOL)
> +
> +#ifndef CONFIG_CMDLINE_OVERRIDE
> +#define GENERIC_CMDLINE_NEED_STRLCAT
> +/*
> + * This function will append or prepend a builtin command line to the command
> + * line provided by the bootloader. Kconfig options can be used to alter
> + * the behavior of this builtin command line.
> + * @dest: The destination of the final appended/prepended string
> + * @src: The starting string or NULL if there isn't one.
> + * @tmp: temporary space used for prepending
> + * @length: the maximum length of the strings above.
> + * @cmdline_strlcpy: point to a compatible strlcpy
> + * @cmdline_strlcat: point to a compatible strlcat
> + */
> +static inline void
> +__cmdline_add_builtin(char *dest, const char *src, char *tmp, unsigned long length,
> + size_t (*cmdline_strlcpy)(char *dest, const char *src, size_t size),
> + size_t (*cmdline_strlcat)(char *dest, const char *src, size_t count))
> +{
> + if (src != dest && src != NULL) {
> + cmdline_strlcpy(dest, " ", length);
> + cmdline_strlcat(dest, src, length);
> + }
> +
> + if (sizeof(CONFIG_CMDLINE_APPEND) > 1)

This test can probably be avoided. if CONFIG_CMDLINE_APPEND is empty, it will add a space at the end
of dest, that's harmless.

> + cmdline_strlcat(dest, " " CONFIG_CMDLINE_APPEND, length);
> +
> + if (sizeof(CONFIG_CMDLINE_PREPEND) > 1) {

Same. Keep it simple. Provide tmp all the time, have only one logic.

> + cmdline_strlcpy(tmp, CONFIG_CMDLINE_PREPEND " ", length);
> + cmdline_strlcat(tmp, dest, length);
> + cmdline_strlcpy(dest, tmp, length);
> + }
> +}
> +
> +#define cmdline_add_builtin_custom(dest, src, length, label, cmdline_strlcpy, cmdline_strlcat) \
> +{ \
> + if (sizeof(CONFIG_CMDLINE_PREPEND) > 1) { \
> + static label char cmdline_tmp_space[length]; \
> + __cmdline_add_builtin(dest, src, cmdline_tmp_space, length, cmdline_strlcpy, cmdline_strlcat); \
> + } else if (sizeof(CONFIG_CMDLINE_APPEND) > 1) { \
> + __cmdline_add_builtin(dest, src, NULL, length, cmdline_strlcpy, cmdline_strlcat); \
> + } \

No need to micro-optimise this, you can provide cmdline_tmp_space all the time and only keep on leg
of the if/elseif

> +}
> +#define cmdline_add_builtin(dest, src, length) \
> + cmdline_add_builtin_custom(dest, src, length, __initdata, strlcpy, strlcat)
> +
> +#else /* CONFIG_CMDLINE_OVERRIDE */
> +
> +static inline void
> +__cmdline_add_builtin_custom(char *dest, const char *src, unsigned long length,
> + size_t (*cmdline_strlcpy)(char *dest, const char *src, size_t size))

Argh ! So the same function as different semantics whether CONFIG_CMDLINE_OVERRIDE and/or
CONFIG_CMDLINE_BOOL is selected ? It means the architecture will have to know it as well in order to
call it right ? That looks like micro-optimisation, I think it is not worth it.


> +{
> + cmdline_strlcpy(dest, CONFIG_CMDLINE_PREPEND " " CONFIG_CMDLINE_APPEND, length);
> +}
> +#define cmdline_add_builtin_custom(dest, src, length, label, cmdline_strlcpy, cmdline_strlcat) \
> + __cmdline_add_builtin_custom(dest, src, length, cmdline_strlcpy)
> +#define cmdline_add_builtin(dest, src, length) \
> + __cmdline_add_builtin_custom(dest, src, length, strlcpy)
> +#endif /* !CONFIG_CMDLINE_OVERRIDE */
> +
> +#else /* !CONFIG_GENERIC_CMDLINE || !CONFIG_CMDLINE_BOOL */
> +
> +static inline void
> +__cmdline_add_builtin_custom(char *dest, const char *src, unsigned long length,
> + size_t (*cmdline_strlcpy)(char *dest, const char *src, size_t size))
> +{
> + if (src != NULL)
> + cmdline_strlcpy(dest, src, length);
> +}
> +#define cmdline_add_builtin_custom(dest, src, length, label, cmdline_strlcpy, cmdline_strlcat) \
> + __cmdline_add_builtin_custom(dest, src, length, cmdline_strlcpy)
> +#define cmdline_add_builtin(dest, src, length) \
> + __cmdline_add_builtin_custom(dest, src, length, strlcpy) \
> +
> +#endif /* CONFIG_GENERIC_CMDLINE */
> +
> +#endif /* _LINUX_CMDLINE_H */
> diff --git a/init/Kconfig b/init/Kconfig
> index 29ad68325028..28363ab07cd4 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -2032,6 +2032,74 @@ config PROFILING
> config TRACEPOINTS
> bool
>
> +config GENERIC_CMDLINE
> + bool
> +
> +if GENERIC_CMDLINE
> +
> +config CMDLINE_BOOL
> + bool "Built-in kernel command line"
> + help
> + Allow for specifying boot arguments to the kernel at
> + build time. On some systems (e.g. embedded ones), it is
> + necessary or convenient to provide some or all of the
> + kernel boot arguments with the kernel itself (that is,
> + to not rely on the boot loader to provide them.)
> +
> + To compile command line arguments into the kernel,
> + set this option to 'Y', then fill in the
> + the boot arguments in CONFIG_CMDLINE.

CONFIG_CMDLINE doesn't exist.

> +
> + Systems with fully functional boot loaders (i.e. non-embedded)
> + should leave this option set to 'N'.
> +
> +config CMDLINE_APPEND
> + string "Built-in kernel command string append"
> + depends on CMDLINE_BOOL

I think it would be better to have CMDLINE_APPEND and CMDLINE_PREPENT defined at all time, and not
leak CMDLINE_BOOL into code. It should just be used here to unable user customisation of
CMDLINE_APPEND, as follows:

config CMDLINE_APPEND
string "Built-in kernel command string append" if CMDLINE_BOOL
default ""


> + default ""
> + help
> + Enter arguments here that should be compiled into the kernel
> + image and used at boot time. If the boot loader provides a
> + command line at boot time, this string is appended to it to
> + form the full kernel command line, when the system boots.
> +
> + However, you can use the CONFIG_CMDLINE_OVERRIDE option to
> + change this behavior.
> +
> + In most cases, the command line (whether built-in or provided
> + by the boot loader) should specify the device for the root
> + file system.
> +
> +config CMDLINE_PREPEND
> + string "Built-in kernel command string prepend"
> + depends on CMDLINE_BOOL

Same comment as for CMDLINE_APPEND

> + default ""
> + help
> + Enter arguments here that should be compiled into the kernel
> + image and used at boot time. If the boot loader provides a
> + command line at boot time, this string is prepended to it to
> + form the full kernel command line, when the system boots.
> +
> + However, you can use the CONFIG_CMDLINE_OVERRIDE option to
> + change this behavior.
> +
> + In most cases, the command line (whether built-in or provided
> + by the boot loader) should specify the device for the root
> + file system.
> +
> +config CMDLINE_OVERRIDE
> + bool "Built-in command line overrides boot loader arguments"
> + depends on CMDLINE_BOOL
> + help
> + Set this option to 'Y' to have the kernel ignore the boot loader
> + command line, and use ONLY the built-in command line. In this case
> + append and prepend strings are concatenated to form the full
> + command line.
> +
> + This is used to work around broken boot loaders. This should
> + be set to 'N' under normal conditions.

In powerpc, by default, when a CMDLINE is provided, it is used only if the bootloader doesn't
provide a command line. I can't see how I can do that here.

> +endif
> +
> endmenu # General setup
>
> source "arch/Kconfig"
>

\
 
 \ /
  Last update: 2021-03-09 08:35    [W:4.453 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site