Re: [PATCH] fix mount option parsing in remount

[Eric Sandeen <sandeen@sandeen.net>]

Christoph Hellwig wrote:
> Remount currently happily accept any option thrown at it, although the
> only filesystem specific option it actually handles is barrier/nobarrier.
> And it actually doesn't handle these correctly either because it only
> uses the value it parsed when we're doing a ro->rw transition.  In
> addition to that there's also a bad bug in xfs_parseargs which doesn't
> touch the actual option in the mount point except for a single one,
> XFS_MOUNT_SMALL_INUMS and thus forced any filesystem that's every
> remounted in some way to not support 64bit inodes with no way to recover
> unless unmounted.
> 
> This patch changes xfs_fs_remount to use it's own linux/parser.h based
> options parse instead of xfs_parseargs and reject all options except
> for barrier/nobarrier and to the right thing in general.  Eventually
> I'd like to have a single big option table used for mount aswell but
> that can wait for a while.
> 
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Index: linux-2.6-xfs/fs/xfs/linux-2.6/xfs_super.c
> ===================================================================
> --- linux-2.6-xfs.orig/fs/xfs/linux-2.6/xfs_super.c	2008-05-18 15:22:23.000000000 +0200
> +++ linux-2.6-xfs/fs/xfs/linux-2.6/xfs_super.c	2008-05-18 15:59:32.000000000 +0200
> @@ -67,6 +67,7 @@
>  #include <linux/writeback.h>
>  #include <linux/kthread.h>
>  #include <linux/freezer.h>
> +#include <linux/parser.h>
>  
>  static struct quotactl_ops xfs_quotactl_operations;
>  static struct super_operations xfs_super_operations;
> @@ -1255,6 +1256,19 @@ xfs_fs_statfs(
>  	return 0;
>  }
>  
> +/*
> + * Eventually we should extend this table and use it for mount, too.

Maybe expand this a little:

/*
 * Today only the barrier/nobarrier xfs mount options are handled
 * on remount.  This table should be expanded to cover all options,
 * and used for the initial mount path, too.
 */

... I'd also like this for the mount path because for example:

mount -t xfs -o barrier=0 /dev/blah /mnt/foo

works... but does not turn off barriers.

So as a first step/example this looks ok but I'd sure like to see it
extended soon.  Maybe when I'm bored... :)

-Eric

> + */
> +enum {
> +	Opt_barrier, Opt_nobarrier, Opt_err
> +};
> +
> +static match_table_t tokens = {
> +	{Opt_barrier, "barrier"},
> +	{Opt_nobarrier, "nobarrier"},
> +	{Opt_err, NULL}
> +};
> +
>  STATIC int
>  xfs_fs_remount(
>  	struct super_block	*sb,
> @@ -1262,36 +1276,54 @@ xfs_fs_remount(
>  	char			*options)
>  {
>  	struct xfs_mount	*mp = XFS_M(sb);
> -	struct xfs_mount_args	*args;
> -	int			error;
> +	substring_t		args[MAX_OPT_ARGS];
> +	char			*p;
>  
> -	args = xfs_args_allocate(sb, 0);
> -	if (!args)
> -		return -ENOMEM;
> +	while ((p = strsep(&options, ",")) != NULL) {
> +		int token;
>  
> -	error = xfs_parseargs(mp, options, args, 1);
> -	if (error)
> -		goto out_free_args;
> +		if (!*p)
> +			continue;
>  
> -	if (!(*flags & MS_RDONLY)) {			/* rw/ro -> rw */
> -		if (mp->m_flags & XFS_MOUNT_RDONLY)
> -		mp->m_flags &= ~XFS_MOUNT_RDONLY;
> -		if (args->flags & XFSMNT_BARRIER) {
> +		token = match_token(p, tokens, args);
> +		switch (token) {
> +		case Opt_barrier:
>  			mp->m_flags |= XFS_MOUNT_BARRIER;
> -			xfs_mountfs_check_barriers(mp);
> -		} else {
> +
> +			/*
> +			 * Test if barriers are actually working if we can,
> +			 * else delay this check until the filesystem is
> +			 * marked writeable.
> +			 */
> +			if (!(mp->m_flags & XFS_MOUNT_RDONLY))
> +				xfs_mountfs_check_barriers(mp);
> +			break;
> +		case Opt_nobarrier:
>  			mp->m_flags &= ~XFS_MOUNT_BARRIER;
> +			break;
> +		default:
> +			printk(KERN_INFO
> +	"XFS: mount option \"%s\" not support for remount\n", p);
> +			return -EINVAL;
>  		}
> -	} else if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {	/* rw -> ro */
> +	}
> +
> +	/* rw/ro -> rw */
> +	if ((mp->m_flags & XFS_MOUNT_RDONLY) && !(*flags & MS_RDONLY)) {
> +		mp->m_flags &= ~XFS_MOUNT_RDONLY;
> +		if (mp->m_flags & XFS_MOUNT_BARRIER)
> +			xfs_mountfs_check_barriers(mp);
> +	}
> +
> +	/* rw -> ro */
> +	if (!(mp->m_flags & XFS_MOUNT_RDONLY) && (*flags & MS_RDONLY)) {
>  		xfs_filestream_flush(mp);
>  		xfs_sync(mp, SYNC_DATA_QUIESCE);
>  		xfs_attr_quiesce(mp);
>  		mp->m_flags |= XFS_MOUNT_RDONLY;
>  	}
>  
> - out_free_args:
> -	kfree(args);
> -	return -error;
> +	return 0;
>  }
>  
>  /*
> 
>