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

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Date: Mon, 10 Jun 2024 13:11:39 -0400
From: Benjamin Marzinski <bmarzins@...hat.com>
To: Abhinav Jain <jain.abhinav177@...il.com>
Cc: agk@...hat.com, snitzer@...nel.org, mpatocka@...hat.com,
        dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
        skhan@...uxfoundation.org, javier.carrasco.cruz@...il.com
Subject: Re: [PATCH] dm: Add support for escaped characters in
 str_field_delimit()

On Sun, Jun 09, 2024 at 02:17:21PM +0000, Abhinav Jain wrote:
> Add a new variable for escaped characters.
> 
> If an escaped character (\) is found before the separator, and if the 
> separator is not found or if the escaped character is located before the
> separator, then move the separator ahead and continue searching for the
> next separator.
> 
> Return the pointer to remainder string after the delimiter. If the
> separator was found, return a pointer to the character immediately after
> the delimiter (s + 1). If the separator was not found, return NULL.

This doesn't do anything to the escape character. Presumably you want to
pass the field containing a separator down to dm_eary_create(). But you
don't want to pass the escape character itself.

To work correctly, this code needs to remove all those escape characters
that come before separators. It probably needs to do something like:

1. Find a next non-escaped separator and change it to NULL, so you have
your field string.

2. Find all the escaped separators in the field string, and shift the
rest of the string over to overwrite the escape character with the rest
of the string.

-Ben

> 
> Signed-off-by: Abhinav Jain <jain.abhinav177@...il.com>
> ---
>  drivers/md/dm-init.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-init.c b/drivers/md/dm-init.c
> index 2a71bcdba92d..bef6a582a4ae 100644
> --- a/drivers/md/dm-init.c
> +++ b/drivers/md/dm-init.c
> @@ -87,11 +87,21 @@ 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;
>  
> -	/* TODO: add support for escaped characters */
>  	*str = skip_spaces(*str);
>  	s = strchr(*str, separator);
> +
> +	/* Check for escaped character */
> +	escaped = strchr(*str, '\\');
> +	if (escaped && (s == NULL || escaped < s)) {
> +		/*
> +		 * If escaped character comes before the separator, move
> +		 * the separator ahead & continue searching for next one.
> +		 */
> +		s = strchr(escaped + 1, separator);
> +	}
> +
>  	/* Delimit the field and remove trailing spaces */
>  	if (s)
>  		*s = '\0';
> -- 
> 2.34.1
>