Re: [PATCH] libxfs: disallow filesystems with reverse mapping and reflink and realtime

Eric Sandeen
2020-09-30T15:31:24Z

On 9/30/20 9:58 AM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
>
> Neither the kernel nor the code in xfsprogs support filesystems that
> have (either reverse mapping btrees or reflink) enabled and a realtime
> volume configured. The kernel rejects such combinations and mkfs
> refuses to format such a config, but xfsprogs doesn't check and can do
> Bad Things, so port those checks before someone shreds their filesystem.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

seems fine in general but a couple thoughts...

> ---
> libxfs/init.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/libxfs/init.c b/libxfs/init.c
> index cb8967bc77d4..1a966084ffea 100644
> --- a/libxfs/init.c
> +++ b/libxfs/init.c
> @@ -724,6 +724,20 @@ libxfs_mount(
> exit(1);
> }
>
> + if (xfs_sb_version_hasreflink(sbp) && sbp->sb_rblocks) {

Hm, we really don't use xfs_sb_version_hasrealtime() very consistently, but it might
be worth doing here?

I wish we had a feature flag to cross-ref against, a corruption in sb_rblocks will lead
to an untouchable filesystem, but I guess there's nothing we can do about that.

Actually, would it help to cross-check against the rtdev arg as well? Should we do anything
different if the user actually specified a realtime device on the commandline?

I mean, I suppose

> + fprintf(stderr,
> + _("%s: Reflink not compatible with realtime device. Please try a newer xfsprogs.\n"),

I like this optimism. ;)

> + progname);
> + exit(1);
> + }
> +
> + if (xfs_sb_version_hasrmapbt(sbp) && sbp->sb_rblocks) {
> + fprintf(stderr,
> + _("%s: Reverse mapping btree not compatible with realtime device. Please try a newer xfsprogs.\n"),
> + progname);
> + exit(1);
> + }
> +
> xfs_da_mount(mp);
>
> if (xfs_sb_version_hasattr2(&mp->m_sb))
>