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

[Glauber Costa]

On 08/15/2011 04:09 AM, Dave Chinner wrote:
> On Sun, Aug 14, 2011 at 07:13:52PM +0400, Glauber Costa wrote:
> > This patch introduces a simple generic vfs option parser.
> > Right now, the only option we have is to limit the size of the dcache.
> >
> > So any user that wants to have a dcache entries limit, can specify:
> >
> >    mount -o whatever_options,vfs_dcache_size=XXX<dev>  <mntpoint>
> >
> > It is supposed to work well with remounts, allowing it to change
> > multiple over the course of the filesystem's lifecycle.
> >
> > I find mount a natural interface for handling filesystem options,
> > so that's what I've choosen. Feel free to yell at it at will if
> > you disagree.
>
> It's already been noted by both myself and Al that there is not a
> 1:1 mapping between mount point and superblocks....

I had skipped that one in my pending patches.

Well, it's already been noted by me as well. And by anybody.
The problem, however, is not new. Filesystems exports fs-specific
options that operate on the superblock as well. And we've been living 
alright with them.

> > @@ -2350,6 +2449,12 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
> >   	else
> >   		retval = do_new_mount(&path, type_page, flags, mnt_flags,
> >   				      dev_name, data_page);
> > +
> > +	/* bind mounts get to respect their parents decision */
> > +	if (!retval&&  !(flags&  MS_BIND))
> > +		vfs_set_dcache_size(path.mnt->mnt_sb,
> > +				    vfs_options.vfs_dcache_size);
> > +			
>
> And I'm not sure that silently ignoring it in certain cases
> is the best way around that problem.

It is not "in certain cases". It is : 1) When bind mounting, and 2) When 
an error occurs. Pretty well-defined.
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