linux-ext4 - Re: [PATCH V2] ext4: handle optional-arg mount options better

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Date:	Mon, 15 Feb 2010 21:23:38 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	tytso@....edu
CC:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH V2] ext4: handle optional-arg mount options better

tytso@....edu wrote:
> Ok, how about this, for even more explicit?
> 
> 						- Ted

Sure, that looks even better.  Who knew args parsing was so hard ;)

-Eric

> commit 15121c18a22ae483279f76dc9e554334b800d0f7
> Author: Eric Sandeen <sandeen@...hat.com>
> Date:   Mon Feb 15 20:17:55 2010 -0500
> 
>     ext4: Fix optional-arg mount options
>     
>     We have 2 mount options, "barrier" and "auto_da_alloc" which may or
>     may not take a 1/0 argument.  This causes the ext4 superblock mount
>     code to subtract uninitialized pointers and pass the result to
>     kmalloc, which results in very noisy failures.
>     
>     Per Ted's suggestion, initialize the args struct so that
>     we know whether match_token() found an argument for the
>     option, and skip match_int() if not.
>     
>     Also, return error (0) from parse_options if we thought
>     we found an argument, but match_int() Fails.
>     
>     Reported-by: Michael S. Tsirkin <mst@...hat.com>
>     Signed-off-by: Eric Sandeen <sandeen@...hat.com>
>     Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 735c20d..68a55df 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1229,6 +1229,11 @@ static int parse_options(char *options, struct super_block *sb,
>  		if (!*p)
>  			continue;
>  
> +		/*
> +		 * Initialize args struct so we know whether arg was
> +		 * found; some options take optional arguments.
> +		 */
> +		args[0].to = args[0].from = 0;
>  		token = match_token(p, tokens, args);
>  		switch (token) {
>  		case Opt_bsd_df:
> @@ -1518,10 +1523,11 @@ set_qf_format:
>  			clear_opt(sbi->s_mount_opt, BARRIER);
>  			break;
>  		case Opt_barrier:
> -			if (match_int(&args[0], &option)) {
> -				set_opt(sbi->s_mount_opt, BARRIER);
> -				break;
> -			}
> +			if (args[0].from) {
> +				if (match_int(&args[0], &option))
> +					return 0;
> +			} else
> +				option = 1;	/* No argument, default to 1 */
>  			if (option)
>  				set_opt(sbi->s_mount_opt, BARRIER);
>  			else
> @@ -1594,10 +1600,11 @@ set_qf_format:
>  			set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
>  			break;
>  		case Opt_auto_da_alloc:
> -			if (match_int(&args[0], &option)) {
> -				clear_opt(sbi->s_mount_opt, NO_AUTO_DA_ALLOC);
> -				break;
> -			}
> +			if (args[0].from) {
> +				if (match_int(&args[0], &option))
> +					return 0;
> +			} else
> +				option = 1;	/* No argument, default to 1 */
>  			if (option)
>  				clear_opt(sbi->s_mount_opt, NO_AUTO_DA_ALLOC);
>  			else

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