Date:   Mon, 25 Jan 2021 20:43:16 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     kgdb-bugreport@...ts.sourceforge.net, jason.wessel@...driver.com,
        dianders@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kdb: Refactor env variables get/set code

On Mon, Jan 25, 2021 at 07:59:45PM +0530, Sumit Garg wrote:
> Move kdb environment related get/set APIs to a separate file in order
> to provide an abstraction for environment variables access and hence
> enhances code readability.
> 
> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> ---
>  kernel/debug/kdb/Makefile      |   2 +-
>  kernel/debug/kdb/kdb_env.c     | 229 +++++++++++++++++++++++++++++++++++++++++
>  kernel/debug/kdb/kdb_main.c    | 201 +-----------------------------------

So... a couple of things bother me about this.

1. This patch mixes together real changes (new functions for example) and
   code motion. That makes is needlessly difficult to review. Code
   motion and changes should always be different patches.

2. I'm rather unconvinced by the premise that removing a continuous
   block of functions from one file to another has a particularly big
   impact on readabiity. The existing environment functions are not
   scattered in many difference places so I think any gain from
   moving them is lost (and then some) by the potential for painful
   merge conflicts, especially if anything needs backporting.

I *think* I like the new functions (though I agree with Doug about the
naming) although it is hard to be entirely sure since they are tangled
in with the code motion.

Basically I'd rather see the patch without the code motion...
something that just extracts some of the ad-hoc environmental scans
into functions and puts the functions near the existing env
manipulation functions.


Daniel.

>  kernel/debug/kdb/kdb_private.h |   3 +
>  4 files changed, 235 insertions(+), 200 deletions(-)
>  create mode 100644 kernel/debug/kdb/kdb_env.c
> 
> diff --git a/kernel/debug/kdb/Makefile b/kernel/debug/kdb/Makefile
> index efac857..b76aebe 100644
> --- a/kernel/debug/kdb/Makefile
> +++ b/kernel/debug/kdb/Makefile
> @@ -6,7 +6,7 @@
>  # Copyright (c) 2009 Wind River Systems, Inc. All Rights Reserved.
>  #
>  
> -obj-y := kdb_io.o kdb_main.o kdb_support.o kdb_bt.o gen-kdb_cmds.o kdb_bp.o kdb_debugger.o
> +obj-y := kdb_io.o kdb_main.o kdb_support.o kdb_bt.o gen-kdb_cmds.o kdb_bp.o kdb_debugger.o kdb_env.o
>  obj-$(CONFIG_KDB_KEYBOARD)    += kdb_keyboard.o
>  
>  clean-files := gen-kdb_cmds.c
> diff --git a/kernel/debug/kdb/kdb_env.c b/kernel/debug/kdb/kdb_env.c
> new file mode 100644
> index 0000000..33ab5e6
> --- /dev/null
> +++ b/kernel/debug/kdb/kdb_env.c
> @@ -0,0 +1,229 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Kernel Debugger Architecture Independent Environment Functions
> + *
> + * Copyright (c) 1999-2004 Silicon Graphics, Inc.  All Rights Reserved.
> + * Copyright (c) 2009 Wind River Systems, Inc.  All Rights Reserved.
> + * 03/02/13    added new 2.5 kallsyms <xavier.bru@...l.net>
> + */
> +
> +#include <linux/kdb.h>
> +#include <linux/string.h>
> +#include "kdb_private.h"
> +
> +/*
> + * Initial environment.   This is all kept static and local to
> + * this file.   We don't want to rely on the memory allocation
> + * mechanisms in the kernel, so we use a very limited allocate-only
> + * heap for new and altered environment variables.  The entire
> + * environment is limited to a fixed number of entries (add more
> + * to __env[] if required) and a fixed amount of heap (add more to
> + * KDB_ENVBUFSIZE if required).
> + */
> +static char *__env[] = {
> +#if defined(CONFIG_SMP)
> +	"PROMPT=[%d]kdb> ",
> +#else
> +	"PROMPT=kdb> ",
> +#endif
> +	"MOREPROMPT=more> ",
> +	"RADIX=16",
> +	"MDCOUNT=8",		/* lines of md output */
> +	KDB_PLATFORM_ENV,
> +	"DTABCOUNT=30",
> +	"NOSECT=1",
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +	(char *)0,
> +};
> +
> +static const int __nenv = ARRAY_SIZE(__env);
> +
> +/*
> + * kdbgetenv - This function will return the character string value of
> + *	an environment variable.
> + * Parameters:
> + *	match	A character string representing an environment variable.
> + * Returns:
> + *	NULL	No environment variable matches 'match'
> + *	char*	Pointer to string value of environment variable.
> + */
> +char *kdbgetenv(const char *match)
> +{
> +	char **ep = __env;
> +	int matchlen = strlen(match);
> +	int i;
> +
> +	for (i = 0; i < __nenv; i++) {
> +		char *e = *ep++;
> +
> +		if (!e)
> +			continue;
> +
> +		if ((strncmp(match, e, matchlen) == 0)
> +		 && ((e[matchlen] == '\0')
> +		   || (e[matchlen] == '='))) {
> +			char *cp = strchr(e, '=');
> +
> +			return cp ? ++cp : "";
> +		}
> +	}
> +	return NULL;
> +}
> +
> +/*
> + * kdballocenv - This function is used to allocate bytes for
> + *	environment entries.
> + * Parameters:
> + *	match	A character string representing a numeric value
> + * Outputs:
> + *	*value  the unsigned long representation of the env variable 'match'
> + * Returns:
> + *	Zero on success, a kdb diagnostic on failure.
> + * Remarks:
> + *	We use a static environment buffer (envbuffer) to hold the values
> + *	of dynamically generated environment variables (see kdb_set).  Buffer
> + *	space once allocated is never free'd, so over time, the amount of space
> + *	(currently 512 bytes) will be exhausted if env variables are changed
> + *	frequently.
> + */
> +static char *kdballocenv(size_t bytes)
> +{
> +#define	KDB_ENVBUFSIZE	512
> +	static char envbuffer[KDB_ENVBUFSIZE];
> +	static int envbufsize;
> +	char *ep = NULL;
> +
> +	if ((KDB_ENVBUFSIZE - envbufsize) >= bytes) {
> +		ep = &envbuffer[envbufsize];
> +		envbufsize += bytes;
> +	}
> +	return ep;
> +}
> +
> +/*
> + * kdbgetulenv - This function will return the value of an unsigned
> + *	long-valued environment variable.
> + * Parameters:
> + *	match	A character string representing a numeric value
> + * Outputs:
> + *	*value  the unsigned long represntation of the env variable 'match'
> + * Returns:
> + *	Zero on success, a kdb diagnostic on failure.
> + */
> +int kdbgetulenv(const char *match, unsigned long *value)
> +{
> +	char *ep;
> +
> +	ep = kdbgetenv(match);
> +	if (!ep)
> +		return KDB_NOTENV;
> +	if (strlen(ep) == 0)
> +		return KDB_NOENVVALUE;
> +
> +	*value = simple_strtoul(ep, NULL, 0);
> +
> +	return 0;
> +}
> +
> +/*
> + * kdbgetintenv - This function will return the value of an
> + *	integer-valued environment variable.
> + * Parameters:
> + *	match	A character string representing an integer-valued env variable
> + * Outputs:
> + *	*value  the integer representation of the environment variable 'match'
> + * Returns:
> + *	Zero on success, a kdb diagnostic on failure.
> + */
> +int kdbgetintenv(const char *match, int *value)
> +{
> +	unsigned long val;
> +	int diag;
> +
> +	diag = kdbgetulenv(match, &val);
> +	if (!diag)
> +		*value = (int) val;
> +	return diag;
> +}
> +
> +/*
> + * kdb_setenv - Alter an existing environment variable or create a new one.
> + * Parameters:
> + *	var	name of the variable
> + *	val	value of the variable
> + * Returns:
> + *	Zero on success, a kdb diagnostic on failure.
> + */
> +int kdb_setenv(const char *var, const char *val)
> +{
> +	int i;
> +	char *ep;
> +	size_t varlen, vallen;
> +
> +	varlen = strlen(var);
> +	vallen = strlen(val);
> +	ep = kdballocenv(varlen + vallen + 2);
> +	if (ep == (char *)0)
> +		return KDB_ENVBUFFULL;
> +
> +	sprintf(ep, "%s=%s", var, val);
> +
> +	ep[varlen+vallen+1] = '\0';
> +
> +	for (i = 0; i < __nenv; i++) {
> +		if (__env[i]
> +		 && ((strncmp(__env[i], var, varlen) == 0)
> +		   && ((__env[i][varlen] == '\0')
> +		    || (__env[i][varlen] == '=')))) {
> +			__env[i] = ep;
> +			return 0;
> +		}
> +	}
> +
> +	/*
> +	 * Wasn't existing variable.  Fit into slot.
> +	 */
> +	for (i = 0; i < __nenv-1; i++) {
> +		if (__env[i] == (char *)0) {
> +			__env[i] = ep;
> +			return 0;
> +		}
> +	}
> +
> +	return KDB_ENVFULL;
> +}
> +
> +/*
> + * kdb_prienv - Display the current environment variables.
> + */
> +void kdb_prienv(void)
> +{
> +	int i;
> +
> +	for (i = 0; i < __nenv; i++) {
> +		if (__env[i])
> +			kdb_printf("%s\n", __env[i]);
> +	}
> +}
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index a0989a0..03ba161 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -129,57 +129,6 @@ static kdbmsg_t kdbmsgs[] = {
>  
>  static const int __nkdb_err = ARRAY_SIZE(kdbmsgs);
>  
> -
> -/*
> - * Initial environment.   This is all kept static and local to
> - * this file.   We don't want to rely on the memory allocation
> - * mechanisms in the kernel, so we use a very limited allocate-only
> - * heap for new and altered environment variables.  The entire
> - * environment is limited to a fixed number of entries (add more
> - * to __env[] if required) and a fixed amount of heap (add more to
> - * KDB_ENVBUFSIZE if required).
> - */
> -
> -static char *__env[] = {
> -#if defined(CONFIG_SMP)
> - "PROMPT=[%d]kdb> ",
> -#else
> - "PROMPT=kdb> ",
> -#endif
> - "MOREPROMPT=more> ",
> - "RADIX=16",
> - "MDCOUNT=8",			/* lines of md output */
> - KDB_PLATFORM_ENV,
> - "DTABCOUNT=30",
> - "NOSECT=1",
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> - (char *)0,
> -};
> -
> -static const int __nenv = ARRAY_SIZE(__env);
> -
>  struct task_struct *kdb_curr_task(int cpu)
>  {
>  	struct task_struct *p = curr_task(cpu);
> @@ -211,113 +160,6 @@ static inline bool kdb_check_flags(kdb_cmdflags_t flags, int permissions,
>  }
>  
>  /*
> - * kdbgetenv - This function will return the character string value of
> - *	an environment variable.
> - * Parameters:
> - *	match	A character string representing an environment variable.
> - * Returns:
> - *	NULL	No environment variable matches 'match'
> - *	char*	Pointer to string value of environment variable.
> - */
> -char *kdbgetenv(const char *match)
> -{
> -	char **ep = __env;
> -	int matchlen = strlen(match);
> -	int i;
> -
> -	for (i = 0; i < __nenv; i++) {
> -		char *e = *ep++;
> -
> -		if (!e)
> -			continue;
> -
> -		if ((strncmp(match, e, matchlen) == 0)
> -		 && ((e[matchlen] == '\0')
> -		   || (e[matchlen] == '='))) {
> -			char *cp = strchr(e, '=');
> -			return cp ? ++cp : "";
> -		}
> -	}
> -	return NULL;
> -}
> -
> -/*
> - * kdballocenv - This function is used to allocate bytes for
> - *	environment entries.
> - * Parameters:
> - *	match	A character string representing a numeric value
> - * Outputs:
> - *	*value  the unsigned long representation of the env variable 'match'
> - * Returns:
> - *	Zero on success, a kdb diagnostic on failure.
> - * Remarks:
> - *	We use a static environment buffer (envbuffer) to hold the values
> - *	of dynamically generated environment variables (see kdb_set).  Buffer
> - *	space once allocated is never free'd, so over time, the amount of space
> - *	(currently 512 bytes) will be exhausted if env variables are changed
> - *	frequently.
> - */
> -static char *kdballocenv(size_t bytes)
> -{
> -#define	KDB_ENVBUFSIZE	512
> -	static char envbuffer[KDB_ENVBUFSIZE];
> -	static int envbufsize;
> -	char *ep = NULL;
> -
> -	if ((KDB_ENVBUFSIZE - envbufsize) >= bytes) {
> -		ep = &envbuffer[envbufsize];
> -		envbufsize += bytes;
> -	}
> -	return ep;
> -}
> -
> -/*
> - * kdbgetulenv - This function will return the value of an unsigned
> - *	long-valued environment variable.
> - * Parameters:
> - *	match	A character string representing a numeric value
> - * Outputs:
> - *	*value  the unsigned long represntation of the env variable 'match'
> - * Returns:
> - *	Zero on success, a kdb diagnostic on failure.
> - */
> -static int kdbgetulenv(const char *match, unsigned long *value)
> -{
> -	char *ep;
> -
> -	ep = kdbgetenv(match);
> -	if (!ep)
> -		return KDB_NOTENV;
> -	if (strlen(ep) == 0)
> -		return KDB_NOENVVALUE;
> -
> -	*value = simple_strtoul(ep, NULL, 0);
> -
> -	return 0;
> -}
> -
> -/*
> - * kdbgetintenv - This function will return the value of an
> - *	integer-valued environment variable.
> - * Parameters:
> - *	match	A character string representing an integer-valued env variable
> - * Outputs:
> - *	*value  the integer representation of the environment variable 'match'
> - * Returns:
> - *	Zero on success, a kdb diagnostic on failure.
> - */
> -int kdbgetintenv(const char *match, int *value)
> -{
> -	unsigned long val;
> -	int diag;
> -
> -	diag = kdbgetulenv(match, &val);
> -	if (!diag)
> -		*value = (int) val;
> -	return diag;
> -}
> -
> -/*
>   * kdbgetularg - This function will convert a numeric string into an
>   *	unsigned long value.
>   * Parameters:
> @@ -374,10 +216,6 @@ int kdbgetu64arg(const char *arg, u64 *value)
>   */
>  int kdb_set(int argc, const char **argv)
>  {
> -	int i;
> -	char *ep;
> -	size_t varlen, vallen;
> -
>  	/*
>  	 * we can be invoked two ways:
>  	 *   set var=value    argv[1]="var", argv[2]="value"
> @@ -422,37 +260,7 @@ int kdb_set(int argc, const char **argv)
>  	 * Tokenizer squashed the '=' sign.  argv[1] is variable
>  	 * name, argv[2] = value.
>  	 */
> -	varlen = strlen(argv[1]);
> -	vallen = strlen(argv[2]);
> -	ep = kdballocenv(varlen + vallen + 2);
> -	if (ep == (char *)0)
> -		return KDB_ENVBUFFULL;
> -
> -	sprintf(ep, "%s=%s", argv[1], argv[2]);
> -
> -	ep[varlen+vallen+1] = '\0';
> -
> -	for (i = 0; i < __nenv; i++) {
> -		if (__env[i]
> -		 && ((strncmp(__env[i], argv[1], varlen) == 0)
> -		   && ((__env[i][varlen] == '\0')
> -		    || (__env[i][varlen] == '=')))) {
> -			__env[i] = ep;
> -			return 0;
> -		}
> -	}
> -
> -	/*
> -	 * Wasn't existing variable.  Fit into slot.
> -	 */
> -	for (i = 0; i < __nenv-1; i++) {
> -		if (__env[i] == (char *)0) {
> -			__env[i] = ep;
> -			return 0;
> -		}
> -	}
> -
> -	return KDB_ENVFULL;
> +	return kdb_setenv(argv[1], argv[2]);
>  }
>  
>  static int kdb_check_regs(void)
> @@ -2056,12 +1864,7 @@ static int kdb_lsmod(int argc, const char **argv)
>  
>  static int kdb_env(int argc, const char **argv)
>  {
> -	int i;
> -
> -	for (i = 0; i < __nenv; i++) {
> -		if (__env[i])
> -			kdb_printf("%s\n", __env[i]);
> -	}
> +	kdb_prienv();
>  
>  	if (KDB_DEBUG(MASK))
>  		kdb_printf("KDBDEBUG=0x%x\n",
> diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
> index 4b2f79e..ae43a13 100644
> --- a/kernel/debug/kdb/kdb_private.h
> +++ b/kernel/debug/kdb/kdb_private.h
> @@ -105,6 +105,9 @@ extern int kdb_putword(unsigned long, unsigned long, size_t);
>  extern int kdbgetularg(const char *, unsigned long *);
>  extern int kdbgetu64arg(const char *, u64 *);
>  extern char *kdbgetenv(const char *);
> +extern int kdbgetulenv(const char *match, unsigned long *value);
> +extern int kdb_setenv(const char *var, const char *val);
> +extern void kdb_prienv(void);
>  extern int kdbgetaddrarg(int, const char **, int*, unsigned long *,
>  			 long *, char **);
>  extern int kdbgetsymval(const char *, kdb_symtab_t *);
> -- 
> 2.7.4
> 

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