On Tue, Aug 11, 2020 at 02:39:01PM -0500, Eric Sandeen wrote:
> On 8/11/20 9:42 AM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > Teach mkfs to set the DAX flag on the root directory so that all new
> > files can be created in dax mode. This is a complement to removing the
> > mount option.
>
> So, a new -d option, "-d dax"
>
> This is ~analogous to cowextsize, rtinherit, projinherit, and extszinherit
> so there is certainly precedence for this. (where only rtinherit is a boolean
> like this, but they are all inheritable behaviors)
>
> (I wonder if "daxinherit" would be more consistent, but won't bikeshed
> that (much))
/me is indifferent either way. But I guess some day we might want to
have a dax= flag to indicate something like "set the data device
geometry to optimize for DAX?
Nah, I think if we were ever going to do that, we'd have something more
like:
-d usage=dax
-d usage=ssd
-d usage=floopy
Meh. I'll change it to daxinherit, since that /is/ what it does.
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > man/man8/mkfs.xfs.8 | 11 +++++++++++
> > mkfs/xfs_mkfs.c | 14 ++++++++++++++
> > 2 files changed, 25 insertions(+)
> >
> >
> > diff --git a/man/man8/mkfs.xfs.8 b/man/man8/mkfs.xfs.8
> > index 9d762a43011a..4b4fdd86b2f4 100644
> > --- a/man/man8/mkfs.xfs.8
> > +++ b/man/man8/mkfs.xfs.8
> > @@ -394,6 +394,17 @@ All inodes created by
> > will have this extent size hint applied.
> > The value must be provided in units of filesystem blocks.
> > Directories will pass on this hint to newly created children.
> > +.TP
> > +.BI dax= value
> > +All inodes created by
> > +.B mkfs.xfs
> > +will have the DAX flag set.
> > +This means that directories will pass the flag on to newly created files
>
> let's call this "children" to match the other similar options?
>
> (because technically it is passed on not only to regular files, right?)
Directories and regular files, though not to other special files.
Maybe we should fix that.
> > +and files will use the DAX IO paths when possible.
> > +This value is either 1 to enable the use or 0 to disable.
> > +By default,
> > +.B mkfs.xfs
> > +will not enable DAX mode.
> > .RE
> > .TP
> > .B \-f
> > diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> > index 2e6cd280e388..33507f6ea21c 100644
> > --- a/mkfs/xfs_mkfs.c
> > +++ b/mkfs/xfs_mkfs.c
> > @@ -60,6 +60,7 @@ enum {
> > D_PROJINHERIT,
> > D_EXTSZINHERIT,
> > D_COWEXTSIZE,
> > + D_DAX,
> > D_MAX_OPTS,
> > };
> >
> > @@ -254,6 +255,7 @@ static struct opt_params dopts = {
> > [D_PROJINHERIT] = "projinherit",
> > [D_EXTSZINHERIT] = "extszinherit",
> > [D_COWEXTSIZE] = "cowextsize",
> > + [D_DAX] = "dax",
> > },
> > .subopt_params = {
> > { .index = D_AGCOUNT,
> > @@ -369,6 +371,12 @@ static struct opt_params dopts = {
> > .maxval = UINT_MAX,
> > .defaultval = SUBOPT_NEEDS_VAL,
> > },
> > + { .index = D_DAX,
> > + .conflicts = { { NULL, LAST_CONFLICT } },
>
> er.... should we conflict with reflink .... ?
>
> > + .minval = 0,
> > + .maxval = 1,
> > + .defaultval = 1,
>
> Hm, interesting that this is a little different from rtinherit:
>
> { .index = D_RTINHERIT,
> .conflicts = { { NULL, LAST_CONFLICT } },
> .minval = 1,
> .maxval = 1,
> .defaultval = 1,
> },
>
> I think this means that:
>
> -d rtinherit
> -d rtinherit=1
>
> are valid, but
>
> -d rtinherit=0 is not, but
>
> -d dax
> -d dax=1
> -d dax=0
>
> are all valid?
TBH, I find it a little odd that you *can't* say "-d rtinherit=0" from a
completeness perspective, but...
> While the latter makes a bit more sense, I wonder if we should stay
> consistent w/ the rtinherit semantics. Or do you envision some sort
> of automatic enabling of this based on device typethat we'd need to
> override in the future?
...the goal is to set this automatically once distros start shipping a
libblkid that has blkid_topology_get_dax(). At that point we'll
probably want a way to force it off.
Unless we want the ability to specify -ddax=0 the magic seekrit hook to
discover if (future) mkfs actually supports dax autodetection? Hmm,
that alone sounds like sufficient justification. Ok.
--D
>
> > + },
> > },
> > };
> >
> > @@ -1434,6 +1442,12 @@ data_opts_parser(
> > cli->fsx.fsx_cowextsize = getnum(value, opts, subopt);
> > cli->fsx.fsx_xflags |= FS_XFLAG_COWEXTSIZE;
> > break;
> > + case D_DAX:
> > + if (getnum(value, opts, subopt))
> > + cli->fsx.fsx_xflags |= FS_XFLAG_DAX;
> > + else
> > + cli->fsx.fsx_xflags &= ~FS_XFLAG_DAX;
> > + break;
> > default:
> > return -EINVAL;
> > }
> >
