On Tue, Apr 26, 2022 at 05:52:14PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
>
> Every time someone changes the transaction reservation sizes, they
> introduce potential compatibility problems if the changes affect the
> minimum log size that we validate at mount time. If the minimum log
> size gets larger (which should be avoided because doing so presents a
> serious risk of log livelock), filesystems created with old mkfs will
> not mount on a newer kernel; if the minimum size shrinks, filesystems
> created with newer mkfs will not mount on older kernels.
>
> Therefore, enable the creation of a shadow log reservation structure
> where we can "undo" the effects of tweaks when computing minimum log
> sizes. These shadow reservations should never be used in practice, but
> they insulate us from perturbations in minimum log size.
>
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_log_rlimit.c | 15 +++++++++++----
> fs/xfs/xfs_trace.h | 12 ++++++++++--
> 2 files changed, 21 insertions(+), 6 deletions(-)
>
>
> diff --git a/fs/xfs/libxfs/xfs_log_rlimit.c b/fs/xfs/libxfs/xfs_log_rlimit.c
> index 67798ff5e14e..4d04568ab07e 100644
> --- a/fs/xfs/libxfs/xfs_log_rlimit.c
> +++ b/fs/xfs/libxfs/xfs_log_rlimit.c
> @@ -14,6 +14,7 @@
> #include "xfs_trans_space.h"
> #include "xfs_da_btree.h"
> #include "xfs_bmap_btree.h"
> +#include "xfs_trace.h"
>
> /*
> * Calculate the maximum length in bytes that would be required for a local
> @@ -46,19 +47,25 @@ xfs_log_get_max_trans_res(
> struct xfs_mount *mp,
> struct xfs_trans_res *max_resp)
> {
> + struct xfs_trans_resv resv;
> struct xfs_trans_res *resp;
> struct xfs_trans_res *end_resp;
> + unsigned int i;
> int log_space = 0;
> int attr_space;
>
> attr_space = xfs_log_calc_max_attrsetm_res(mp);
>
> - resp = (struct xfs_trans_res *)M_RES(mp);
> - end_resp = (struct xfs_trans_res *)(M_RES(mp) + 1);
> - for (; resp < end_resp; resp++) {
> + memcpy(&resv, M_RES(mp), sizeof(struct xfs_trans_resv));
Looks much nicer, but I had to read on further into the patchset
before it made sense. As it all ends up ok:
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
--
Dave Chinner
david@xxxxxxxxxxxxx
