linux-kernel - Re: [PATCH v2] dm: Add support for escaped characters in str_field

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Message-ID: <c5133ae3-1655-3364-a272-68cae447b490@redhat.com>
Date: Tue, 2 Jul 2024 17:18:38 +0200 (CEST)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Abhinav Jain <jain.abhinav177@...il.com>
cc: agk@...hat.com, snitzer@...nel.org, dm-devel@...ts.linux.dev, 
    linux-kernel@...r.kernel.org, bmarzins@...hat.com, 
    skhan@...uxfoundation.org, javier.carrasco.cruz@...il.com
Subject: Re: [PATCH v2] dm: Add support for escaped characters in
 str_field_delimit()

Hi

I'd like to ask why is this needed. AFAIK, none of the allowed targets use 
',' on their table line.

Mikulas


On Thu, 13 Jun 2024, Abhinav Jain wrote:

> Remove all the escape characters that come before separator.
> Tested this code by writing a dummy program containing the two
> functions and testing it on below input, sharing results:
> 
> Original string: "field1\,with\,commas,field2\,with\,more\,commas"
> Field: "field1"
> Field: "with"
> Field: "commas"
> Field: "field2"
> Field: "with"
> Field: "more"
> Field: "commas"
> 
> Signed-off-by: Abhinav Jain <jain.abhinav177@...il.com>
> ---
> PATCH v1:
> https://lore.kernel.org/all/20240609141721.52344-1-jain.abhinav177@gmail.com/
> 
> Changes since v1:
>  - Modified the str_field_delimit function as per shared feedback
>  - Added remove_escaped_characters function
> ---
> ---
>  drivers/md/dm-init.c | 53 +++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 47 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
> index 2a71bcdba92d..0e31ecf1b48e 100644
> --- a/drivers/md/dm-init.c
> +++ b/drivers/md/dm-init.c
> @@ -76,6 +76,24 @@ static void __init dm_setup_cleanup(struct list_head *devices)
>  	}
>  }
>  
> +/* Remove escape characters from a given field string. */
> +static void __init remove_escape_characters(char *field)
> +{
> +	char *src = field;
> +	char *dest = field;
> +
> +	while (*src) {
> +		if (*src == '\\') {
> +			src++;
> +			if (*src)
> +				*dest++ = *src++;
> +		} else {
> +			*dest++ = *src++;
> +		}
> +	}
> +	*dest = '\0';
> +}
> +
>  /**
>   * str_field_delimit - delimit a string based on a separator char.
>   * @str: the pointer to the string to delimit.
> @@ -87,16 +105,39 @@ static void __init dm_setup_cleanup(struct list_head *devices)
>   */
>  static char __init *str_field_delimit(char **str, char separator)
>  {
> -	char *s;
> +	char *s, *escaped, *field;
>  
> -	/* TODO: add support for escaped characters */
>  	*str = skip_spaces(*str);
>  	s = strchr(*str, separator);
> -	/* Delimit the field and remove trailing spaces */
> -	if (s)
> +
> +	/* Check for escaped character */
> +	escaped = strchr(*str, '\\');
> +	while (escaped && (s == NULL || escaped < s)) {
> +		/*
> +		 * Move the separator search ahead if escaped
> +		 * character comes before.
> +		 */
> +		s = strchr(escaped + 1, separator);
> +		escaped = strchr(escaped + 1, '\\');
> +	}
> +
> +	/* If we found a separator, we need to handle escape characters */
> +	if (s) {
> +		*s = '\0';
> +
> +		remove_escape_characters(*str);
> +		field = *str;
> +		*str = s + 1;
> +	} else {
> +		/* Handle the last field when no separator is present */
> +		s = *str + strlen(*str);
>  		*s = '\0';
> -	*str = strim(*str);
> -	return s ? ++s : NULL;
> +
> +		remove_escape_characters(*str);
> +		field = *str;
> +		*str = s;
> +	}
> +	return field;
>  }
>  
>  /**
> -- 
> 2.34.1
>