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

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

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.

Any interest in allowing people to specify the value too?  Seeing as we
allow that the sysfs version of the interface.

--D

> +
>  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
> 
>