Re: [PATCH v3 4/4] parse options in the vfs level

[Glauber Costa]

On 08/14/2011 08:39 AM, Vasiliy Kulikov wrote:
> Hi Glauber,
>
> On Sun, Aug 14, 2011 at 19:13 +0400, Glauber Costa wrote:
> > +/**
> > + * Generic option parsing for the VFS.
> > + *
> > + * Since most of the filesystems already do their own option parsing, and with
> > + * very few code shared between them, this function strips out any options that
> > + * we succeed in parsing ourselves. Passing them forward would just give the
> > + * underlying fs an option it does not expect, leading it to fail.
> > + *
> > + * We don't yet have a pointer to the super block as well, since this is
> > + * pre-mount. We accumulate in struct vfs_options whatever data we collected,
> > + * and act on it later.
> > + */
> > +static int vfs_parse_options(char *options, struct vfs_options *ops)
> > +{
> > +	substring_t args[MAX_OPT_ARGS];
> > +	int option;
> > +	char *p;
> > +	char *opt;
> > +	char *start = NULL;
> > +	int ret;
> > +	
> > +	if (!options)
> > +		return 0;
> > +
> > +	opt = kstrdup(options, GFP_KERNEL);
> > +	if (!opt)
> > +		return 1;
> > +	
> > +	ret = 1;
> > +
> > +	start = opt;
> > +	while ((p = strsep(&opt, ",")) != NULL) {
> > +		int token;
> > +		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 1:
> > +			if (!args[0].from)
> > +				break;
> > +
> > +			if (match_int(&args[0],&option))
> > +				break;
>
> What if there are 2 passed options and the second fails?
>
>     mount -o vfs_dcache_size=XXX,vfs_dcache_size=CRAP<dev>  <mntpoint>
>
> In this case you leave the second option and pass it to the fs option
> parser (as you already set ret=0), which is wrong.  I think you should
> explicitly return 1 where you know the option is related to VFS, but you
> failed to parse it.  It would look even simplier than current code.

Good point, thank you. I agree.

> (Yes, this is a rare situation, but I can imagine some program that
> automatically adds mount options to the existing list and passes it to
> mount.)
Absolutely.
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