Re: [PATCH 06/10] xfs: allow setting errortags at mount time

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jan 28, 2026 at 12:30:05PM +0100, Carlos Maiolino wrote:
> On Tue, Jan 27, 2026 at 05:05:46PM +0100, Christoph Hellwig wrote:
> > Add an errortag mount option that enables an errortag with the default
> > injection frequency.  This allows injecting errors into the mount
> > process instead of just on live file systems, and thus test mount
> > error handling.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  Documentation/admin-guide/xfs.rst |  6 ++++++
> >  fs/xfs/xfs_error.c                | 36 +++++++++++++++++++++++++++++++
> >  fs/xfs/xfs_error.h                |  4 ++++
> >  fs/xfs/xfs_super.c                |  8 ++++++-
> >  4 files changed, 53 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/admin-guide/xfs.rst b/Documentation/admin-guide/xfs.rst
> > index c85cd327af28..cb8cd12660d7 100644
> > --- a/Documentation/admin-guide/xfs.rst
> > +++ b/Documentation/admin-guide/xfs.rst
> > @@ -215,6 +215,12 @@ When mounting an XFS filesystem, the following options are accepted.
> >  	inconsistent namespace presentation during or after a
> >  	failover event.
> >  
> > +  errortag=tagname
> > +	When specified, enables the error inject tag named "tagname" with the
> > +	default frequency.  Can be specified multiple times to enable multiple
> > +	errortags.  Specifying this option on remount will reset the error tag
> > +	to the default value if it was set to any other value before.
> > +
> 
> I think this should include the fact it is only supported with DEBUG
> enabled.
> I'm sure we'll get user complains about why 'errortag=foo' is not working?
> And, in some unfortunate case somebody has DEBUG enabled when they
> shouldn't have, at least the documentation says so this shouldn't be
> used...

Should we explicitly state here that the errortag=XXX will /not/ be
echoed back via /proc/mounts?  Seeing as we recently had bug reports
about scripts encoding /proc/mounts into /etc/fstab.

(That's why I hate mount options)

--D

> I'm happy taking this patch though and we work on the above later, so...
> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
> 
> >  Deprecation of V4 Format
> >  ========================
> >  
> > diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
> > index 53704f1ed791..d652240a1dca 100644
> > --- a/fs/xfs/xfs_error.c
> > +++ b/fs/xfs/xfs_error.c
> > @@ -22,6 +22,12 @@
> >  static const unsigned int xfs_errortag_random_default[] = { XFS_ERRTAGS };
> >  #undef XFS_ERRTAG
> >  
> > +#define XFS_ERRTAG(_tag, _name, _default) \
> > +        [XFS_ERRTAG_##_tag]	=  __stringify(_name),
> > +#include "xfs_errortag.h"
> > +static const char *xfs_errortag_names[] = { XFS_ERRTAGS };
> > +#undef XFS_ERRTAG
> > +
> >  struct xfs_errortag_attr {
> >  	struct attribute	attr;
> >  	unsigned int		tag;
> > @@ -189,6 +195,36 @@ xfs_errortag_add(
> >  	return 0;
> >  }
> >  
> > +int
> > +xfs_errortag_add_name(
> > +	struct xfs_mount	*mp,
> > +	const char		*tag_name)
> > +{
> > +	unsigned int		i;
> > +
> > +	for (i = 0; i < XFS_ERRTAG_MAX; i++) {
> > +		if (xfs_errortag_names[i] &&
> > +		    !strcmp(xfs_errortag_names[i], tag_name))
> > +			return xfs_errortag_add(mp, i);
> > +	}
> > +
> > +	return -EINVAL;
> > +}
> > +
> > +void
> > +xfs_errortag_copy(
> > +	struct xfs_mount	*dst_mp,
> > +	struct xfs_mount	*src_mp)
> > +{
> > +	unsigned int		val, i;
> > +
> > +	for (i = 0; i < XFS_ERRTAG_MAX; i++) {
> > +		val = READ_ONCE(src_mp->m_errortag[i]);
> > +		if (val)
> > +			WRITE_ONCE(dst_mp->m_errortag[i], val);
> > +	}
> > +}
> > +
> >  int
> >  xfs_errortag_clearall(
> >  	struct xfs_mount	*mp)
> > diff --git a/fs/xfs/xfs_error.h b/fs/xfs/xfs_error.h
> > index b40e7c671d2a..05fc1d1cf521 100644
> > --- a/fs/xfs/xfs_error.h
> > +++ b/fs/xfs/xfs_error.h
> > @@ -45,6 +45,8 @@ void xfs_errortag_delay(struct xfs_mount *mp, const char *file, int line,
> >  #define XFS_ERRORTAG_DELAY(mp, tag)		\
> >  	xfs_errortag_delay((mp), __FILE__, __LINE__, (tag))
> >  int xfs_errortag_add(struct xfs_mount *mp, unsigned int error_tag);
> > +int xfs_errortag_add_name(struct xfs_mount *mp, const char *tag_name);
> > +void xfs_errortag_copy(struct xfs_mount *dst_mp, struct xfs_mount *src_mp);
> >  int xfs_errortag_clearall(struct xfs_mount *mp);
> >  #else
> >  #define xfs_errortag_init(mp)			(0)
> > @@ -52,6 +54,8 @@ int xfs_errortag_clearall(struct xfs_mount *mp);
> >  #define XFS_TEST_ERROR(mp, tag)			(false)
> >  #define XFS_ERRORTAG_DELAY(mp, tag)		((void)0)
> >  #define xfs_errortag_add(mp, tag)		(-ENOSYS)
> > +#define xfs_errortag_copy(dst_mp, src_mp)	((void)0)
> > +#define xfs_errortag_add_name(mp, tag_name)	(-ENOSYS)
> >  #define xfs_errortag_clearall(mp)		(-ENOSYS)
> >  #endif /* DEBUG */
> >  
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index ee335dbe5811..d5aec07c3a5b 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -40,6 +40,7 @@
> >  #include "xfs_defer.h"
> >  #include "xfs_attr_item.h"
> >  #include "xfs_xattr.h"
> > +#include "xfs_error.h"
> >  #include "xfs_errortag.h"
> >  #include "xfs_iunlink_item.h"
> >  #include "xfs_dahash_test.h"
> > @@ -112,7 +113,7 @@ enum {
> >  	Opt_prjquota, Opt_uquota, Opt_gquota, Opt_pquota,
> >  	Opt_uqnoenforce, Opt_gqnoenforce, Opt_pqnoenforce, Opt_qnoenforce,
> >  	Opt_discard, Opt_nodiscard, Opt_dax, Opt_dax_enum, Opt_max_open_zones,
> > -	Opt_lifetime, Opt_nolifetime, Opt_max_atomic_write,
> > +	Opt_lifetime, Opt_nolifetime, Opt_max_atomic_write, Opt_errortag,
> >  };
> >  
> >  #define fsparam_dead(NAME) \
> > @@ -171,6 +172,7 @@ static const struct fs_parameter_spec xfs_fs_parameters[] = {
> >  	fsparam_flag("lifetime",	Opt_lifetime),
> >  	fsparam_flag("nolifetime",	Opt_nolifetime),
> >  	fsparam_string("max_atomic_write",	Opt_max_atomic_write),
> > +	fsparam_string("errortag",	Opt_errortag),
> >  	{}
> >  };
> >  
> > @@ -1581,6 +1583,8 @@ xfs_fs_parse_param(
> >  			return -EINVAL;
> >  		}
> >  		return 0;
> > +	case Opt_errortag:
> > +		return xfs_errortag_add_name(parsing_mp, param->string);
> >  	default:
> >  		xfs_warn(parsing_mp, "unknown mount option [%s].", param->key);
> >  		return -EINVAL;
> > @@ -2172,6 +2176,8 @@ xfs_fs_reconfigure(
> >  	if (error)
> >  		return error;
> >  
> > +	xfs_errortag_copy(mp, new_mp);
> > +
> >  	/* Validate new max_atomic_write option before making other changes */
> >  	if (mp->m_awu_max_bytes != new_mp->m_awu_max_bytes) {
> >  		error = xfs_set_max_atomic_write_opt(mp,
> > -- 
> > 2.47.3
> > 
> > 
>